Pacific Science (1987), vol. 41, nos. 1- 4
© 1988 by the University of Hawaii Press. All rig hts reserved
Laboratory Growth, Reproduction and Life Span of the Pacific Pygmy Octopus,
Octopus digueti'
RANDAL H . D ER USHA , JOHN W. FORSYTHE AND R OGER T. HANLON
2
ABSTRACT: Octopus digueti Perrier and Rochebrune, 1894 was reared through
its life cycle at 25°C in a closed seawater system using artificial sea water. Two
field-collected females produced 231 hatchlings: 193 hatchlings were group 
cultured while 24 were isolated at hatching and grown individually to allow
precise analyses ofgrowth in length and weight over the life cycle. All octopuses
were fed primarily live shrimps. Maturing adults fed at a rate of 4.7% of body
weight per day and had a gross growth efficiency of 48% . Growth in weight was
exponential for the first 72 days and described best by the equation: WW(g) =
.0405e·0646t. The mean growth rate over this period was 6.4% increase in body
weight per day (% jd) , with no significant difference between male and female
growth. From 72 to 143 days , growth was logarithmic and described best by the
equation: WW(g) = (6.78 x 1O-
6
)t
3
.
13
. Females grew slightly faster than males
over this growth phase. During the exponential growth phase, mantle length
increased at a mean rate of 2.1% per day, declining to 1.1% per day over the
logarithmic phase. No attempt was made to describe mathematically the period
of declining growth rate beyond day 143. The primary causes ofearly mortality
in group culture were escapes and cannibalism. Survival was good despite high
culture density: 73% survival to date of first egg laying (day Il l). Survival was
better among the isolated growth-study octopuses: 88% to the date of first egg
laying (day 130). Mean life span was 199 days in group-reared octopuses and
221 days in the growth-study octopuses. There was no significant difference
between male and female life span. Progeny of the group culture were reared at
similar stocking densities and fed predominantly fresh dead shrimp and crab
meat. This diet resulted in cannibalism, with only 6% survival to first egg laying
on day 128. Fecundity in this group was lower. Octopus digueti is a good
candidate for laboratory culture and biological experimentation because of its
small size, rapid growth, short life span, and good survival in group culture.
O CTOPUS DIGUETI PERRIER AND R OCHEBRUN E,
1894 is a small, benthic octopod inhabiting
tidal flats in the northern Gulf of California
(lat. 31°N, long. 114°W). Octopus digueti
(Figure I) shares several morphological and
ecological characteristics with the Atlantic
pygmy octopus, Octopusjoubini Robson, 1929,
and the Pacific blue-ringed octopus, Hapalo 
chlaena maculosa Robson, 1929: similar adult
size (20 to 60 g), large egg size (8 to 9 mm,
Figure 1), short life cycle (5 to 8 months at
25°C), and the habit of living within empty
mollusc shells (Tranter and Augustine, 1973;
Hanlon, 1983a; Hanlon and Forsythe, 1985).
To date there is no published information on
the biology and life history of Octopus digueti.
We present here basic life cycle information
that will contribute to ecological studies and
to the evaluation of this species for use in
laboratory culture and biological studies.
MATERIALS AND METHODS
The closed culture systems and method 
ology are described in detail in Forsythe and
104
t Manuscript accepted February 1987.
2The Marine Biomedical Institute, The University of
Texas Medical Branch, 200 University Boulevard, Gal 
veston, Texas 77550-2772.
The Pacific Pygmy Octopus-DERuSHA, FORSYTHE, AND HANLON 105
FIGURE I. A. Embryos of O. digueti at three stages of development (25C): freshly laid, 3 to 4 weeks and ventral
view at 5 to 6 weeks (immediately prior to the second reversal). B. An adult female O. digueti (ML approximately 5ern).
Hanlon (1980) and Hanlon and Forsythe
(1985). Briefly, the culture system consisted
of a 2 m diameter circular fiberglass water 
conditioning tank, 75 ern deep, of approxi 
mately 2000 I capacity and was the site of all
water-conditioning processes. Two fiberglass
culture troughs, 2.4 m x 68 em x 30 cm, were
supported on the upper rim of the water 
conditioning tank and received freshly filtered
artificial seawater (Instant Ocean®) continu 
ously. All octopuses were cultured within these
troughs.
Two female octopuses inhabiting mollusc
shells (Pecten sp. and Muricanthus sp.) were
collected in the northern Gulf of California
near Puerto Penasco, Sonora, Mexico. They
were transported to the University ofArizona
(Tucson), where they laid eggs in aquaria
prior to shipment to Galveston. The brooding
females were packed in separate plastic bags
containing approximately 31 ofsea water and
an equal volume ofpure oxygen, then shipped
by air to Galveston. Upon arrival they were
placed directly into a culture system with the
same temperature and salinity. A culture ofO.
joubini was in progress in the system at that
time .
The two brooding females and their eggs
were kept in separate plexiglass chambers
(19 em x 14 em x 10 em) with nylon screen
sides (800 j1m), which allowed water circulation
but prevented escape of hatchling octopuses.
With the onset of hatching, hatchlings were
removed from the chambers daily, counted
and placed into shallow (water depth, 3-4em)
hatchling trays (50 em x 40 cm) within the
main group culture troughs. One hundred
ninety-three octopuses were placed into the
group culture over a 23-day period. This
group-reared population was provided with
increased horizontal space as animal size in 
creased, the first occurring on day 21 when
half of the population was placed into a sec 
ond hatchling tray.
Twenty-four hatchlings less than 15 hours
old (nine from brood I, 15 from brood 2) were
isolated in individual growth chambers to al 
low precise measurements for a growth study
through the full life cycle. The sides of the
tightly lidded chambers (7 em x 5 em) were
replaced with fine nylon screen. The chambers
were supported in the culture trough and
supplied with strong water circulation. The
octopuses were given larger dens and growth
chambers as they grew.
Hatchlings in both the group culture and
growth study were fed ad libitum on live
mysidacean shrimps. As the octopuses grew,
they were provided larger live foods, progres 
sing from mysidacean shrimp (3-10 mm)
to palaemonid grass shrimp (7-25 mm) to
penaeid shrimp (2-6 ern). Crabs, fishes, and
gastropods of appropriate size supplemented
the shrimp diet.
Beginning at hatching, each animal in the
isolated growth study was measured every 14
106
days. Measurements included: wet weight
(WW), mantle length (ML) and total length
(TL) (Forsythe, 1981; 1984). Dial calipers
were used to measure length to the nearest 0.1
mm, and an electronic balance accurate to
0.01 g was used for all wet-weight measure 
ments . To facilitate length measurement, the
octopuses were narcotized for 90 to 120 sec 
onds in a solution containing 1.5% ethyl al 
cohol and 1.5% ethyl carbamate in sea water.
Excess water was removed by draining the
mantle and blotting the epidermis with a
moist paper towel. Octopuses were then
weighed and manipulated as necessary for
length measurements. All measurements re 
quired approximately 2 minutes total, after
which the octopuses were returned to their
chambers where they revived without assis 
tance in 1 to 2 minutes. A random sample of
15 individuals from the group culture (over
10% of population) was weighed once per
month starting on day 41. These animals were
not measured for ML or TL so they did not
require narcotization. Wet weights were taken
by blotting excess moisture from the animal's
epidermis with a moist paper towel and plac 
ing the octopus in a tared beaker of sea water
on the balance.
For each chronological series oflength and
weight measurements, a line of best fit to
the data was generated by least-squares linear
regression and an equation describing the
growth curve generated. The following equa 
tions were tested to generate lines ofbest fit to
the growth data: linear, y = a + bx; exponen 
tial, y = ae'"; and power, y = ax". In these
equations y = length or weight, x = age in
days, a = the y intercept, b = the slope and
e = the natural logarithm of2. Length-weight
and allometric growth relationships were ex 
amined using the above power function.
Equations describing the best fit to these rela 
tionships were generated in the same manner
as described above. Growth rates were cal 
culated using the instantaneous coefficient of
growth "g" calculated from the equation:
InY
2
-lnY
l
g=
t
2
- t
l
where Y, and Y
2
are lengths or weights at times
t
l
and t
2
. Multiplying g by 100 gives the in-
PACIFIC SCIENCE, Volume41, 1987
stantaneous relative growth rate as percent
increase in body size per day . Multiplying g by
mean lengths or weights over the given time
interval gives a growth rate as mm /day or
g/day,
The food intake ofsix octopuses (2 males, 4
females) from the growth study group was
measured over a 41-day period (days 97-138)
to estimate feeding rates and gross growth
efficiencies (GGE). Each octopus' daily ration
oflive shrimps was blotted dry and weighed to
the nearest 0.01 g, while the previous day's
food remains from that animal's chamber
were collected and weighed . The amount of
food ingested by each octopus was estimated
by subtracting the weight ofuneaten exoskele 
tons from the weight of the whole living
shrimps; this amount was referred to as the
ingested weight (IW). By dividing the ingested
weight by the number ofdays in that interval,
feeding rate was determined as grams of
shrimp tissue eaten per day (g/day). Feeding
rates were also calculated as percent of body
weight (BW) ingested per day (%BW/day)
from the equation: %BW/day = IW/WWt,
where t is the time period in days and WW is
the mean wet weight during that time period
(Choe, 1966; Mangold and Boletzky, 1973).
Gross growth efficiency (GGE) was calcu 
lated over a given period by dividing the in 
crease in wet weight of the octopus by the
ingested weight and multiplying by 100 (Van
Heukelem, 1976).
Since the octopuses in the growth study
were reared individually, it was possible to
compare males and females over the entire life
cycle with respect to all growth data obtained.
Comparisons of means of male and female
growth data were examined using at-test
(Sokal and Rohlf, 1969: 200), after a variance
ratio test (Zar, 1974: 101) was performed to
assure that the means came from normally
distributed populations. An analysis of co 
variance (Zar, 1974: 228) was used to test for
differences in slopes and elevations of linear
forms ofcalculated growth curves.
The progeny of the first laboratory-reared
generation were group-cultured at a density
equivalent to that in the first culture. From
hatching, this group of octopuses was regu 
larly fed both freshly killed and frozen foods
The Pacific Pygmy Octopus-c-Dnlcusnx, FORSYTHE, AND HANLON 107
to evaluate the usefulness of such alternatives
to live foods. Living octopuses were counted
periodically to determine survival. No growth
study was attempted with this group; how 
ever, all fatalities were weighed immediately
after death.
RESULTS
Water Quality
Water quality in the transport bags con 
taining females and eggs remained good dur 
ing the 9-hour trip from Arizona to Texas.
Only NH
4
levels were higher in the bags (0.7
mg/l) than in the culture system that they were
transferred into. The exposure of embryos to
temporarily high NH
4
levels had no obvious
deleterious effects on development and sub 
sequent hatching success. Water quality con 
ditions in the culture system remained stable
over the course of this study. Fluctuations
were insignificant and of short duration. The
mean temperature throughout the experiment
was 24.9°C (range 21-27°C). Mean salinity
was 35.2 ppt (range 33.0-37.5 ppt) and mean
pH 7.9 (range 7.5-8.2). Biologicalfiltration was
effective: ammonia-nitrogen levels never ex 
ceeded the safe upper limit of 0.1 mg/l (Spotte,
1979; Hanlon and Forsythe, 1985), nitrite 
nitrogen concentrations were consistently be 
low 0.1 mg/l (with only one measurement re 
corded above this level), and nitrate-nitrogen
levels exceeded 200 mg/l once (for 2 weeks),
with the mean value being 117.9 mg/l (range
41.2-235 mg /l),
Hatching
Hatching occurred over a 23-day period
resulting in a total of231 hatchlings from both
broods. Five dead embryos were found after
hatching ended, while an additional nine
hatchlings were apparently unviable and died
within 24 hours after hatching. The modal
hatching day was 10 days after first hatching.
All of the growth-study octopuses hatched
on the modal day. For standardization, the
hatching day of the growth-study octo 
puses was considered day I for the entire
experiment.
Foods and Feeding
Octopus digueti is an aggressive predator
and will generally eat any crustacean, gas 
tropod, fish, or other mollusc that is small
enough for the octopus to subdue. Within
hours after hatching they attacked and con 
sumed live mysidacean shrimp of lengths ex 
ceeding their own. At 23 days (average WW
approx. 0.2 g) they were able to kill and
consume crabs with 2 em carapace width ,
small palaemonid shrimps, and fish. When
quantities of live foods of appropriate size
were not available, pieces of finely cut fresh or
frozen shrimp and crab meat were eaten as
well. The octopuses showed a preference for
live crabs, but ate live shrimp consistently as
the primary diet. Fish and gastropods were
eaten less frequently than shrimp when all
were provided equally.
The mean feeding rate for six octopuses
examined over a 41-day period beginning on
day 97 on a live shrimp diet was 4.7% ofbody
wet weight per day (Table 1). The mean feed 
ing rate was 4.8%(d for females and 4.6%(d
for males. Mean gross growth efficiency (GGE)
was 48.1% . Mean male and female GGEs
were the same. The range ofGGE values from
weekly estimations was wide (Table 1) 
16.4% to 98.2%.
Growth
Growth measurements were taken every 2
weeks from hatching to day 169, by which
time five of the 12 growth-study females had
laid eggs. Each octopus was weighed imme 
diately after death.
GROWTH IN WEIGHT: The growth-study octo 
puses increased from a mean wet weight of
0.04 g (range 0.03-0.06 g, n = 21) at hatching
to an overall mean wet weight of 39.00 g
(range 13.00-68.70 g, n = 21) at 169 days
(Table 2). In comparison, mean wet weight at
death for the 17 growth-study octopuses that
died of natural senescence, from day 171 to
day 258, was 28.3 g (range 7.7-44.9 g). At
every weighing, mean female wet weight was
greater than that of males. Mean female
weight at 169 days was 44.13 g (range 18.45 
68.70 g, n = 13) versus 30.68 g for males
108
TA BLE I
PACIFIC SCIENCE, Volume 41, 1987
FEEDING RATES AND GROSS GROWTH EFFICIENCY (GGE) OF SIXG ROWTH-STUDYOCTOPUSES. Feeding rates are
given as percent of wet bod y weight ingested per day (% jd) and grams of shrimp tissue ingested per day (gjd).
GGE is in percent (%). Combined (male + female), Male and Female data arc given. On day 130 a female laid
eggs and ceased feeding.
FEEDING RATES GGE
GROWTH
INTERVAL (% jd) (gjd) (%)
(DAYS) n MEAN S.D. RANGE MEAN S.D. RANGE MEAN S.D . RANGE
97- 104 6 Combined 4.6 0.6 3.8-5.2 0.8 0.1 0.8- 0.9 45.6 15.8 26.1- 67.4
2 Mal e 4.9 0.4 4.6- 5.1 0.8 0.0 0.8-0.8 51.6 22.4 35.7-67.4
4 Female 4.4 0.7 3.8-5.2 0.8 0.1 0.8-0.9 42.6 14.5 26.1- 61.4
104-11 8 6 Combined 5.8 1.3 4.6- 7.5 1.3 0.4 0.8-1.8 56.2 21.2 41.4-98.2
2 Mal e 4.7 0.1 4.6-4.8 0.9 0.1 0.8- 1.0 51.5 7.9 45.9-57.1
4 Female 6.3 1.3 5.0-7.5 1.6 0.3 1.2-1.8 58.6 26.6 41.4-98.2
118-124 6 Combined 4.9 2.1 2.0- 8.2 1.4 0.9 0.6-3.1 61.2 15.9 49.2-92.0
2 Mal e 5.4 1.3 4.5- 6.3 1.2 0.2 1.1-1.4 57.3 5.9 53.1-61.4
4 Female 4.6 2.6 2.0-8.2 1.5 l.l 0.6- 3.1 63.2 19.8 49.2- 92.0
124-131 5 Combined 4.3 0.6 3.4-5.0 1.4 0.4 1.1-2.0 38.9 15.7 16.4-54.4
2 Male 4.4 0.3 4.2-4.6 1.2 0.0 1.2- 1.2 52.4 2.9 50.3-54.4
3 Female 4.2 0.8 3.4- 5.0 1.6 0.5 1.1-2.0 30.0 13.8 16.4-44.0
131-138 5 Combined 3.9 1.3 2.9-6.2 1.5 0.9 1.1- 3.2 34.8 7.7 23.8- 43.5
2 Male 3.6 0.3 3.4- 3.8 1.1 0.0 1.1-1.1 28.1 6.0 23.8- 32.3
3 Female 4.1 1.8 2.9-6.2 1.8 1.2 1.1- 3.2 39.4 4.9 33.9- 43.5
Overall 28 Combined 4.72 1.4 2.0-8.2 1.3 0.6 0.6- 3.2 48.1 18.0 16.4-98.2
values 10 Male 4.59 0.8 3.4-6.3 1.0 0.2 0.8-1.4 48.2 13.7 23.8- 67.4
18 Fema le 4.80 1.7 2.0-8.2 1.5 0.7 0.6- 3.2 48.1 20.4 16.4- 98.2
(range 13.00-38.70 g, n = 8), a statistically
significant difference (p = 0.05).
Growth rates were highest over the first
10 weeks (Ta ble 2), with an overall mean of
6.41% increase in bod y weight per day (% jd),
which produced a doubling in weight every
12 days. Growth was exponential and de 
scribed best by the equation:
WW(g) = .0405e·06461; r
2
= .9993 (I)
Males and females showed this same pattern
of growth:
male WW(g) = .0381e·06481; r
2
= .9993 (2)
female WW (g) = .041ge·
o64S
t; r
2
= .9992 (3)
There was no significant difference between
the slopes and elevations ofgrowth curves for
males and females.
Beyond 10 weeks, growth slowed and be 
came logarithmic in form through day 143.
Over this period, growth rates declined from
4.68 to 1.50% jd , with a mean overall growth
rate of 3.02% jd . Growth over this period was
described best by the equation:
WW(g) = (6.78 x 1O-
6
W·
1 3
; r
2
= .9885
(4)
Equations for male and female growth were:
male WW(g) = (2.47 x 1O-S )t
2
.
82
;
r
2
= .9857 (5)
female WW(g) = (3.57 x 1O-6)t
3
.
28;
r
2
= .9889 (6)
An analysis of covariance showed the
slopes ofmale and female growth cur ves to be
significantly different over this time period
(p < 0.001). Thus, females were increasing in
weight at a significantly higher rate than were
males of the same age. During this period the
overall growth rate for females was 3.1% jd
compared to 2.8% jd for males . On a gram 
per-day basis, females were growing at a mean
rate of 0.58 gjd versus 0.39 gjd for males
(Table 2).
The first appearance of the hectocotylus in
The Pacific Pygmy Octopus-DERuSHA, FORSYTHE, AND HANLON 109
TABLE 2
GROWTH IN WET WEIGHT (WW) OF GROWTH-STUDY O CTOPUSES. Ateach measurement period the mean weight,
standard deviation (s.d.) and range arc listed for Combined (male + female), Male and Female data. Growth rates
are given as % increase in body weight per day (% /d) and increase in grams per day (g/d). Doubling time is the
number of days required to double in weight at the corresponding growth rate
MEAN RANGE GROWTH RATE DOUBLING
DAY (g) S.D. % /d gld TIME
Combined I 0.04 0.01 0.03- 0.06
n = 21 IS 0.11 0.02 0.07- 0.13 6.66 0.01 10.41
29 0.25 0.04 0.19- 0.33 6.13 0.02 11.31
43 0.69 0.14 0.52- 1.02 7.14 0.05 9.70
58 1.79 0.37 1.29- 2.71 6.34 0.11 10.93
72 4.00 0.71 2.95- 5.44 5.76 0.23 12.04
86 7.70 1.50 5.66-11.22 4.68 0.36 14.80
100 13.73 3.12 9.25-21.75 4.13 0.57 16.79
114 19.51 5.24 10.88-31.18 2.51 0.49 27.64
128 26.82 7.59 13.59-44.06 2.27 0.61 30.50
143 33.57 10.76 14.43-55.66 1.50 0.50 46.29
156 37.07 13.11 14.23-60.87 0.76 0.28 91.00
169 39.00 15.15 13.00-68.70 0.39 0.15 176.97
Male I 0.04 0.01 0.03- 0.05
n=8 15 0.10 0.02 0.07- 0.12 6.81 0.01 10.18
29 0.24 0.03 0.19- 0.28 5.88 0.01 11.79
43 0.64 0.10 0.52- 0.78 7.15 0.05 9.70
58 1.71 0.29 1.35- 2.14 6.54 0.11 10.61
72 3.85 0.70 3.04- 5.03 5.79 0.22 11.96
86 7.21 1.29 5.66- 9.07 4.47 0.32 15.49
100 12.18 2.18 9.25-15.46 3.74 0.46 18.52
114 16.53 3.37 10.88-21.70 2.18 0.36 31.75
128 21.00 4.03 13.59-26.34 1.71 0.36 40.49
143 27.07 7.13 14.43-37.36 1.69 0.46 40.96
156 30.13 8.17 14.23-40.84 0.82 0.25 84.34
169 30.68 8.14 13.00-38.70 0.14 0.04 498.04
Female I 0.04 0.01 0.04- 0.06
n = 13 15 0.11 0.02 0.07- 0.13 6.57 0.01 10.55
29 0.26 0.04 0.19- 0.33 6.27 0.02 11.06
43 0.72 0.16 0.52- 1.02 7.14 0.05 9.70
58 1.83 0.41 1.29- 2.71 6.23 0.11 11.12
72 4.09 0.73 2.95- 5.44 5.73 0.23 12.09
86 8.01 1.58 6.16-11.22 4.80 0.38 14.44
100 14.69 3.29 10.60-21.75 4.33 0.64 15.99
114 21.34 5.44 15.20-31.18 2.67 0.57 25.99
128 30.40 7.09 18.72-44.06 2.53 0.77 27.45
143 37.57 10.85 20.07-55.66 1.41 0.53 49.07
156 41.34 13.98 19.18-60.87 0.73 0.30 94.33
169 44.13 16.41 18.45-68.70 0.50 0.22 138.00
growth-study males on day 86 coincided with laying . The period of declining growth rate
the time of transition from exponential to beyond the end of the logarithmic phase rep-
logarithmic growth. After day 143, growth resented a substantial portion (35%) of the
ceased to be logarithmic in form. Between life cycle. No attempt was made to describe
days 143 and 169, five females and two males growth in weight mathematically beyond day
of the 21 growth-study octopuses had nega- 143.
tive growth rates due to senescence and egg Growth in the group-culture population re-
110 PACIFIC SCIENCE, Volume 41, 1987
TABLE 3
GROWTH IN MANTLE L ENGTH (ML) AND TOTA L L ENGTH (TL) OF GROWTH-STUDY O CTOPUSES. Only the c o m b in ed
(male + female) data are given
MANTLE LENGTH
GROWTH RATE DOUBLING
DAY (mm) S.D. RANGE % / d mm /d TIME
Combined I 5.37 0.47 4.10-6.00
n= 21 15 7.50 0.43 6.45-8.30 2.39 0.18 29.03
29 9.68 0.49 8.80-10.50 1.82 0.18 38.11
43 12.96 1.02 11.20-15.70 2.08 0.27 33.25
58 19.50 1.76 17.20- 23.80 2.72 0.53 25.47
72 24. 10 1.72 20.48- 27.50 1.52 0.37 45.73
86 29.25 2.73 25.00-33.00 1.38 0.40 50.17
100 38.76 2.84 33.80-43.40 2.01 0.78 34.47
114 43.44 3.84 37.20-50.20 0.81 0.35 85.11
128 49.46 4.62 40.00-59.00 0.93 0.46 74.78
143 52.71 5.92 43.00-65.00 0.43 0.22 163.02
156 56.95 7.23 40.00-71.00 0.59 0.34 116.53
169 57.62 8.91 40.00-74.00 0.09 0.05 774.28
TOTAL LENGTH
GROWTH RATE DOUBLING
DAY (mm) S.D. RANGE % / d mm/d TIME
Combined I 11.94 1.80 7.40- 14.15
n = 21 15 19.10 2.52 14.15- 22.50 3.36 0.64 20.65
29 27.20 2.43 22.90- 30.80 2.53 0.69 27.44
43 39.85 3.76 32.80- 47.60 2.73 1.09 25.41
58 59.75 5.19 53.00- 74.00 2.70 1.61 25.66
72 75.31 6.08 64.30- 84.00 1.65 1.24 41.94
86 94.03 8.49 76.30-107.40 1.59 1.49 43.70
100 115.09 9.10 97.30-127.30 1.44 1.66 48.03
114 132.95 12.71 105.70-160.00 1.03 1.37 67.26
128 144.79 14.75 114.00-173.00 0.61 0.88 113.72
143 156.57 20.37 105.00-190.00 0.52 0.82 132.91
156 170.57 25.89 125.00-221.00 0.66 1.12 105.22
169 169.86 27.70 106.00-215.00 - 0.03 - 0.05 -2147.32
sembled that seen in the growth study. The
mean growth rate calculated from group cul 
ture subsample weights at days 41 and 72 was
6.4%/d. There was no statistically significant
difference between growth curves of the group
culture and the growth study in the exponen 
tial phase.
From days 72 to 156, growth slowed to the
logarithmic form and growth rates declined
from 5.6% /d to 0.6% /d, with a mean of
2.3% /d . Growth in the group culture was
significantly slower than the growth study in
the logarithmic phase , resulting in a lower
mean wet weight at the age of spawning.
Crowding and the inclusion of dead foods in
the group culture diet from day 86 contributed
to this difference.
GROWTH IN LENGTH: Tables 3 and 4 sum 
marize growth, growth rates and equations
for mantle length and total length . Like
growth in weight, growth in length was ex 
ponential from day I to 72 and logarithmic
from day 72 to 143. With one exception (ML
at day 100), mean growth rates for mantle
length and total length dimensions were high 
est over the first 72 days (Table 3). Analysis of
covariance showed no statistically significant
The Pacific Pygmy Octopus-DERuSHA, FORSYTHE, AND H ANLON
TA BLE 4
OVERA LL GROWTH RATES (%/0) AND EQUATION VALUES FOR GROWTH IN MANTLE LENGTH(ML) ANDTOTAL
LENGTH (TL) OVER THE Two GROWTH PHASES. Only the y-intercept (a) and slope (b) values for the general
equations are listed. The coefficients ofcorrelati on (r") are also given
III
EXPONENTIAL PHASE(DAYS 1-72) LOGARITHMIC PHASE (DAYS 72-143)
ML or TL = ae'" ML or TL = at"
GROWTH RATE GROWTHRATE
ML (% /d) a b r
2
(% /d) a b r
2
Co mbined 2.1I 5.31 0.0214 0.9962 1.11 0.152 1.19 0.9798
Male 2.08 5.32 0.0212 0.9958 1.01 0.261 1.07 0.9651
Female 2.13 5.30 0.0215 0.9963 1.17 0.11 I 1.26 0.9836
GROWTH RATE GROWTH RATE
TL (% /d) a b r
2
(% /d) a b r
2
Combined 2.59 12.5 0.026 1 0.9928 1.04 0.754 1.08 0.9853
Ma le 2.64 11.9 0.0265 0.9912 0.94 1.088 0.99 0.9719
Female 2.57 12.8 0.0259 0.9935 1.09 0.614 1.14 0.9889
difference in the slope or elevation ofthe male
and female growth curves over either growth
ph ase. There was a sharp increase in mantle
length growth rate between days 86 and 100
for both males and females (see Table 3), after
which gro wth rates slowed. There was no such
increase in growth rate for total length. The
increase in mantle growth rate corresponded
roughly with the time of sexual development
in the grow th-study octopuses (male hecto 
cotylus development on da y 86, first mating
observations on day 88) and first egg laying
(day 130).
LENGTH-WEIGHT RELATIONSffiPS: Since pre 
vious analyses ofgrowth in weight and length
had shown two different growth phases over
the life cycle, the mantle length versus wet
weight data corresponding to the measure 
men t intervals from days I to 72 and 72 to 143
were evaluated separately. An analysis of co 
variance revealed a highly significant differ 
ence (p < 0.00 I) in the slopes of the length 
weight (LfW) relationship over these two time
intervals. The first phase was described best
by the equation:
WW (g) = (2.54 x 10-
4
) ML(mm)3.03;
r
Z
= .9971 (7)
and the second ph ase (72-143 days) by the
equation:
WW(g) = (1.04 x 10-
3)
ML(mm)Z.61;
r
Z
= .9946 (8)
An analysis of covariance between male and
female data showed no significant differences
over either growth phase.
For the benefit of field studies where the
age of an octopus is unknown, a single LjW
equation from days I to 143 (Figure 2) was
calculated:
WW(g) = (3.19 x 10-
4
) ML(mm)Z.93;
r
Z
= .9979 (9)
ALLOMETRIC GROWTH: Post-hatching growth
produced no dramatic changes in body shape
or proportions, although subtle changes did
occur. The slope of the LfW relationship is a
general indicator of allometry in body shape
(Simpson et aI., 1960; Forsythe , 1984). A slope
of 3.0 indicates isometric body growth, with
length and weight increasing in constant pro 
portion to one another. Significant fluctua 
tions above and below 3.0 can indicate allo 
metri c growth and a change in overall body
shape. Based upon this (equation 7), growth
appears isometric during the exponential
growth phase and allometric during the loga 
rithmic growth phase, resulting in a greater
increase in mantle length per unit increase of
weight in the second phase.
100
50
10
5
-C)
-
J-
:::c
(9
-
1.0
w
$
J-
0.5
w
$
0.1
0.05
WW = (3.19 x 10-
4
) ML
2
.
93
,2 = .9979
5 10 50 100
MANTLE LENGTH (mm)
FIGURE 2. The overall (days I to 169) length-weight relationship for O. digueti taken from combined mean wet
weight and mantle length data in Tables 2 and 3.
The Pacific Pygm y Octopus-DERuSHA, F ORSYTHE, AND HANLON 113
Linear body proportions changed slightly
over the life cycle. In Figure 3, the percentage
oftotal length represented by mantle length is
plotted versus age. (Subtracting the mantle
length percentage from 100% closely approxi 
mates arm length percentage.) At hatch 
ing, mantle length represented 45% of total
length, but this percentage gradually declined
to a low of 31% at day 86. Beyond day 100
the percentage stabilized near 34% (±1%).
Using the power function, growth in mantle
length was compared to growth in total length
over both periods, with mantle length the
dependent variab le. The slope of this func 
tion is the constant of allometry. When the
constant of allometry equals 1.0, growth of
mantle length is proportional to growth in
total length (i.e., isometric). Whi le the L/W
relationship was isometric during the expo 
nential growth phase, linear growth was
allometric as characterized by a constant
of allometry of 0.817. This shows that total
length was increasing in greater proportions
to mantle length. This is substantiated by the
higher growth rates in TL versus ML (Table 4)
and agrees with the decrease in ML% in Fig 
ure 3. During the logarithmic growth phase,
where the L/W relationship became allomet 
ric, linear growth had a constant ofallometry
of 1.1 indicating very slight allometry in favor
of mantle length growth over total length.
Mantle length growth rates are slightly higher
than TL (Table 4) and it is during this phase
that ML% increases from the low of 31% to
nearly 34% (Figure 3).
Reproductive Biology
The first external sign ofsexual maturation
was the development of the male's third right
arm into the hectocotylus (used for sper 
matophore transfer). Among growth-study
males, it was recogn izab le on da y 86. Matings
in group culture octopuses were observed
shortly thereafter on day 88. Mating style was
consistent, with the mating pair fairly dis 
tant, often remaining in separate dens, and
the male 's hectocotylized third right arm
stretched to span the distance. Matings were
seen both day and night.
The first laboratory egg laying occurred in
the group culture on day Il l . Egg laying
45
Octopus digueti ----.
Octopus joubini l::r-----C::.
8 40
.....
x
.....J
I 
<,
.....J 35
~
30
40 80 120 160
AGE (days)
FIGURE 3. Allom etric growth: change in mantl e length
as percent of tot al length over the life cycle for O. digueti
and O.joubini. Data for O.joubin i from Forsythe (1981).
began in the growth study on day 130 al 
tho ugh no mating had occured. Growth 
study females were then paired with gro up 
cultured males. Several of these males were
killed by the females and no mating was ob 
served . Primary egg deposits were small
(fewer than ten eggs) and each egg was fas 
tened individually to den walls. Egg laying in
individual broods continued for 2 to 3 weeks,
with final brood sizes ranging from ten to 125
eggs. Three fema les from group culture were
isolated with freshly laid broods for monitor 
ing egg development at 25°C (eggs taken for
measurements were from these broods). Mean
egg length (Figure 1) at laying was 7.9 mm
(range 7.2- 9.0 mm, n = 15). Mean egg width
was 2.8 mm (range 2.6-3.0 mm, n = 15).
Mean wet weight was 0.03 g. Eyespots (retinal
pigmentation) became visible after 3 weeks at
25°C (Table 5) and the second reversal (Bol 
etzky, 1969) occurred at 5 weeks. After the
second reversal, eggs were more sensitive to
114 PACIFIC SCIENCE, Volume 41 , 198 7
T ABLE 5
E GG D EVELOPMENT AND H ATCHI NG OBSERVATIONS ON BROODS OF E GGS LAID AND MAINTAI NED IN THE LABORATORY
AT DIFFERENT T EMPERATURES
MEAN FIRST SECOND DEVELOPMENT HATCHI NG PERCENT
TEMP . ( RANGE) EYFSPOTS REVERSAL TIME DURATION HATCHI NG FEMALE'S NO.
(0C)
VISIBLE (d) (d) (d) SUCCESS ORIGIN EGGS
16.0 (13.5-18.5) 130 28 91 lab 13
16.0 (13.5 -18.5) 133 30 100 lab 7
19.5 (17.0-22.2) 54 68 25 100 wild 100
19.9 (17.0-22.2) 53 62 30 100 wild 75
20.8 (19.5- 22.3) 24 57 18 99 wild 142
2I.I (19.5-24.5) 57 13 100 wild 92
2I.I (19.5-24.5) 59 15 100 wild 18
2I.I (19.5 -24.5) 53 13 100 wild 61
2\.2 (19.5-24.5) 56 9 100 wild 94
21.2 (19.5-24.5) 53 16 wild 54
2\.2 (20.0- 22.3) 25 52 16 100 wild 100
2\.2 (20.0-22.3) 23 52 12 100 wild 17
2\.4 (19.5-24.5) 60 24 93 wild 59
2\.4 (20.3-22.3) 56 27 100 wild 173
2 \.4 (20.0 -24.0) 30 60 14 100 wild 79
24.9 (24.0-25.5) 50 16 100 lab II
25. I (25.0-25.8) 36 26 100 lab 125
25.3 (24.5-26.0) 34 41 29 100 lab 113
handling, so fewer eggs were measured. After
the second reversal mean egg length increased
by approximately 12% to 8.8 mm (range 8.1 
9.6 mm, n = 6), mean egg width increased by
35% to 3.6 mm (range 3.3-4.1 mm, n = 6)
and mean egg wet weight doubled to 0.06 g.
Hatching occurred approximately one week
after second reversal. Mean development time
of those three broods was 42 days (range 36 
50 days) at 25°C and mean hatching duration
was 24 days (range 16-29 days).
The effect oftemperature on the rate of egg
development was dramatic (Table 5). The
duration of egg development increased from a
mean of42 days at 25°C to a mean of 132days
at 16°C. The mean development times of 18
broods of O. digueti, laid and maintained in
four different culture systems, were plotted
against their respective mean temperatures. A
line of best fit to the data was calculated by a
least-squares linear regression resulting in the
logarithmic equation:
Development time (days)
=(7.74 x 10
4
) Temp (oq-2.35; r
2
= .9010
Mortality
There was nearly 23% mortality in the first
month of first generation group-culture (Fig 
ure 4). An actual count 8 days after hatching
ended (day 21 of experiment) showed 22 octo 
puses unaccounted for (II % of stock popu 
lation). Complete cannibalism or undetected
escape are the only possible explanations for
the missing animals. The remaining mortal 
ities were due to cannibalism (4.6%), escapes
(1.5%) and unknown causes (4.6%). Hatch 
lings were observed crawling 6 to 7 em above
the water line to escape; therefore after day 21,
polystyrene lids were kept on the hatchling
trays .
Overall mean survival in group-culture was
145 days (range 1-235 days) . Seventy-three
percent of the stock population (71 females
and 70 males) survived to day Ill, the first egg
laying. Survival of brooding females beyond
hatching was variable, but mean survival
beyond final hatching of the three monitored
females was 16 days (range 12-20 days) .
Survival in the growth study was good.
The Pacific Pygmy Octopus-DERuSHA, FORSYTHE, AND HANLON 115
LU
200
>
--J 160
0::«
LUCJ)
120
COLU
~CJ)
~~
80
Za..
0
I-
40
U
0
first mating
!
first egg laying
f irst hatching
~~G-R-O-""U-P....!..........CU-L...I.T-U-R-E---'~
GROWTH STUDY
20 40 60 80 100 120 140 160 180 200 220 240
AGE (days)
F IGURE 4 . Survival of group-culture and growth-stud y octopuses.
During the second week, one octopus died
without apparent cause and one was crushed
trying to squeeze under its chamber lid. One
more juvenile died while escaping on day 53.
The remaining 21 octopuses (88%) lived be 
yond first egg laying (day 130) and into senes 
cence (see below). Overall mean survival in the
growth study was 192days (range 9-258 days,
n = 20).
Cannibalism and escape from culture trays
were the primary causes ofjuvenile mortality,
accounting for 17.5% of the entire first gen 
eration group culture in the first month (Fig 
ure 4). These two categories of mortality are
combined since missing animals could have
been either escapees or victims of complete
cannibalism.
Aggression and cannibalism continued at
lower levels throughout the period of sexual
maturation, accounting for five of the seven
deaths between days 34 and 118 involving
both males and females.
Deaths caused by natural degeneration or
senescence began abruptly in the group cul 
ture on day 125 and became the dominant
cause of mortality. Senescent mortalities of
males and females began at the same time.
Disease was not a significant cause ofmor 
tality . There were only ten deaths attributed to
disease. This was surprising since they were
sharing a tank system with a culture group of
O.joubini that had a lethal Vibrio spp . bacte 
rial infection (Hanlon et al., 1984).
Senescence in females began with egg lay 
ing and brooding. Females stopped feeding
abruptly from a week to several days before
egg laying, after which they did not leave the
den . They guarded and groomed their eggs
throughout development and defended their
broods vigorously. Prey organisms that blun 
dered into the den were either repelled or
killed, but were usually discarded uneaten.
Without feeding, the females degenerated
graduall y, loosing bulk, muscle tone and nor 
mal skin coloration. Brooding females usually
survived through hatching, but there were
some early deaths ofbrooding females and of
females with unlaid eggs. Ma les degenerated
physically in the same way and at the same
time as the brooding females; however, feeding
activity in males decreased gradually over
several weeks.
Second Generation Survival
Hatching of progeny from group culture
octopuses at 25°C occurred over 53 days , with
a total of 622 hatchlings from approximately
20 broods. Four hundred and three hatchlings
were placed into one large group-culture tray
(0.4 m") as they hatched, and were fed pri 
mari ly dead food (freshly cut pa laemonid
116
shrimps). Day I for this generation was defined
as the day of first hatching. Two hundred
and nineteen octopuses were preserved upon
hatching to control culture density. The first
count of living octopuses was on day 33, after
321 hatchlings had been added to the group.
There were 153 remaining or 48% of those
added. Eighty-two fresh hatchlings were
added to the culture group between days 33
and 46. By day 59 only 112 octopuses re 
mained, 28% of the total. It appeared that
older octopuses were cannibalizing younger
animals, therefore the first hatching day was
used to :approximate the age of survivors
rather than the modal hatching day of the
entire population. Six percent of the popula 
tion (II females and 15 males) survived to the
day of first egg laying (day 128). Only one of
the three broods laid (all fewer than ten eggs)
was observed to be fertile. All eggs were des 
troyed by the females or conspecifics shortly
thereafter.
Life Span
Mortalities occurring after the onset ofegg
laying, within a study population, were at 
tributed to old age or senescence if no other
cause was apparent, and were used to approx 
imate life span. Overall mean life span in the
first generation group culture was 199 days
(range 125-240 days , n = 116; discounting 15
animals used in experimentation and ten that
were killed by conspecifics). Mean life span
for females was 196 days (range 125-230
days, n = 64) and 203 days for males (range
136-240 days, n = 52). There was no statisti 
cally significant difference between male and
female life span. Mean life span in the growth
study was 221 days (range 171 -258 days ,
n = 17). Mean life span for females was 218
days (range 171 -258 days, n=9) and for
males it was 225 days (range 191 -243 days,
n = 8). Again, there was no significant differ 
ence between male and female life span. The
difference in life span in the group culture (199
days) versus that of the growth study (221
days) was slightly significant (p < 0.05). The
life span of the progeny from the first group
culture population was 170 days (range 134 
208 days , n = 21); mean age for females was
171 days (range 143-208 days , n = 9) and for
PACIFIC SCIENCE, Volume 41 ,1987
males was 169 days (range 134-204 days,
n = 12). There was no significant difference
between male and female data. At this time we
can offer no clear explanation for the differ 
ence in life span of these three populations.
In evaluating the effect of reduced tem 
perature on egg development, a dramatic in 
crease in the life span of brooding females was
observed. Two females from the first labora 
tory generation began laying eggs on day 170
and were moved to another system then grad 
ually acclimated from 25°C to 16°C over
several weeks. These two females would have
been expected to live another 20 to 30 days at
25°C, however they both survived another 167
days (to day 338), dying within 24 hours of
each other. Itseems likely that life spans could
exceed a year if animals were cultured at 16°C
for the full life cycle.
DISCUSSION
Octopus digueti is now the third small octo 
pus species for which there are laboratory
data on growth, reproductive biology and life
span . Similar information exists for Octopus
joubini (Opresko and Thomas, 1975; Hanlon,
1983a; Forsythe, 1984)and useful, though less
extensive, data have been reported for Hapa 
lochlaena maculosa (Tranter and Augustine,
1973). Although found in three widely differ 
ent water masses , these three species all have
large eggs, benthic hatchlings, and grow to a
maximum adult size of less than 80 g and 80
mm ML in under one year. Further compari 
sons can be made to other large-egged octopus
species that grow to much larger adult sizes.
Comparisons ofOctopus digueti . o. joubini
and Hapalochlaena maculosa
In the following paragraphs where only two
species are compared there are no comparable
data for the third species. The feeding rates
and gross growth efficiencies determined for
O. digueti were typical of data reported for O.
joubini and other octopus species (see reviews
in Boyle, 1983; Forsythe, 1984) indicating O.
digueti has comparable metabolic capabilities.
Both O. digueti and o. joubini hatch at the
same size and begin growing exponentially at
The Pacific Pygmy Octopu s- D ERu SHA, F ORSYTHE, AND H ANLON 117
TABLE 6
\
LABORATORY DATA ON GROWTH, REPRODUCDVE BIOLOGY AND LIFESPAN FOR SIX SPECIES OF
LARGE-EGGED OCTOPUSES
OCTOPUS OCTOPUS HAPALOCHLAENA OCTOPUS OCTOPUS OCTOPUS
DIGUETI JOUBINI MACULOSA B1MACULOIDES BRIAREUS MAYA
Tem pera tu re eC) 25 25 20 23 25 25
Maximum Ad ult Size (g) 70 35 848 1100 5700
Hatching WW (mg) 40 40 70 95 100
H atchin g M L (mm) 5.4 5.8 4.0 6.5 7.0 7.0
Overa ll Growth Ra te 6.4 7.0 4.6 4.6 6.0
(% BW/d ) Exponen tial
Ph ase
Overa ll Growth R at e 3.0 1.7 1.7 1.7 2.7
(% BW/d) Logar ithmic
Ph ase
No. WW D oublings 6.7 2.8 9.5 8.4 9.5
Exponential Ph ase
Size at En d of 4.0 0.28 52 45 58
Exponential Ph ase (g)
D ura tion of Expo nen tial 42 28 142 140 105
Ph ase (d)
Estimat ed life span (mo) 7 8 7 12 12 10
% Life Span in 36 12 35 39 35
Expo nent ial Ph ase (%)
No. Eggs /Brood 50-1 50 50-200 150 250- 750 300- 700 300-5000
No. Eggs/g of BW 2.0 5.7 0.85 0.63 0.88
Egg Length (mm) 7-8 6-7 6-7 10- 17 12- 13 11-17
Durat ion of Egg 35- 40 35- 40 40-50 46- 50 55-75 45
D evelopment (d)
Egg Development as % 18 15 21 13 18 15
of Life Spa n
Referen ces Presen t Hanlon , T rant er & Forsythe & Hanlon, Van H eukelem ,
study 1983a A ugust ine, Hanlon, 1983b 1976, 1983
F orsythe, 1973 1988 &
1984 unpub. data
similar growth rates (Table 6). The exponen 
tial phase is follo wed by a slower logarithmic
ph ase in both species. The major difference
in growth is the duration of the exponential
phase: 72 versus 28 da ys, respecti vely. Both
species have logarithmic ph ases with similar
growth rates and du ration, but O. digueti
achieves four more doublings in size during its
exponenti al phase than O. jo ubini (Ta ble 6),
thus O. digueti grows to a larger final size.
Mantle length growth ra tes are similar
among the three species of pygmy octopuses
being near 2.0% /d during the exponential
phase and near I.O % /d in the loga rithmic
phase (Forsythe, 1984). Th e durations of the
grow th ph ases again produce different growth
patterns despite the similarities in growth
rates (F igure 5). Because of its extended ex-
ponential grow th ph ase, Octopus digueti ha s
the largest mantle length of the three pygmy
octopuses beyond hatching. Th e growth
curves of O. joubini and H. maculosa parallel
one another to day 60, with O.joubini slightly
larger. The greater gro wth rat e of H. maculosa
produces larger mantle lengths th an O.joubini
beyond day 75 and a growth curve more
closely resembling that of O. digueti. Octopus
jo ubini maintains a nearl y linear pattern of
mantle length growth throughout its lifespan.
Growth analyses related to body shape and
proportion yield quite different results for
O. digueti and O. joubini. The slopes of the
length/weight relation ship ar e quite different
throughout the life cycle. Octopus joubini
weigh more than O. digueti ofthe same mantle
length. The slope values suggest positive allo-
20 60 100 140 180
AGE (days)
FIGURE 5. Mantle length growth up to 6 months ofage
for O. digueti, O.joubini (Forsythe, 1984), O. bimaculoides
(Forsythe and Hanlon, 1988), O. briareus (Forsythe and
Hanlon, unpub. data) and Hapalochlaena maculosa
(Tranter and Augustine, 1973).
metric body growth (slope> 3.0) throughout
the life cycle for O. joubini (Forsythe, 1984)
versus early isometric growth followed by
negative allometry (slope < 3.0) for O. digueti.
Both species show a gradual decline in the
mantle length 's proportion to total body
length (Figure 4) during the first third of the
life cycle, meaning the arms are increasing in
proportion to the mantle. This proportion
stabilizes during the final two-thirds ofthe life
cycle. However, O. joubini has a consistently
shorter mantle length relative to total length
(Figure 4), thus indicating it has longer arms
than O. digueti of the same mantle length.
Despite the differences suggested by the above
observations, simultaneous observations of
both species in this laboratory reveal that dif 
ferences in overall body shape are not striking.
Octopus digueti and O.joubini are very similar
octopuses.
Strong similarities can be seen in most
aspects of the reproductive biology of the
three species. Octopus digueti males develop a
hectocotylus and begin mating at 3 months of
age (25°C), while O.joubini (reviewed in Han 
lon, 1983a) and H. maculosa (Tranter and
Augustine, 1973) require another month at
similar temperatures. Egg-laying also begins a
month sooner for O. diguetithan H. maculosa
and O.joubini, although the latter species can
spawn as early as O. digueti when reared at
27 to 29°C (Thomas and Opresko, 1973). Fe 
cundity in all three species is very similar,
although it is noteworthy that H. maculosa
carries its eggs (Tranter and Augustine, 1973)
while O. digueti and O. joubini both individ 
ually attach theirs to the walls oftheir den site.
The duration of egg development in O. digueti
and O. joubini is near 40 days at 25°C, and
probably from 40 to 50 days at 22°C for H.
maculosa (see Opresko and Thomas, 1975).
Octopus digueti and O. joubini, like many
other octopus species (Ambrose, 1981), show
a negative correlation between water tempera 
ture and egg development time. Hatching
duration is at least I to 2 weeks in all three
species and can last up to 4 weeks in O. digueti
and O. joubini (Hanlon, 1983a). At constant
temperatures, hatching duration is almost cer 
tainly a reflection of the time span over which
eggs are laid. For these small species, egg lay 
ing is apparently not a single rapid episode,
but rather a gradual accretion over a relatively
long period of time. A female O. digueti that
lays eggs over a 3-week period has spawned
for a period of time equivalent to 10% of its
entire life span.
From laboratory growth studies it seems
clear that all three of these small octopus
species are capable of completing their life
cycle in 6 to 7 months if temperatures remain
above 20°e. Comparing animals reared in 
dividually at 25°C, O. digueti has a slightly
shorter mean life span than O. joubini: 7 ver 
sus 8 months, respectively. At these tempera 
tures , the maximal age attained by O. digueti
has been 258 days versus 331 days for O.
joubini (Forsythe, 1984). There is no differ 
ence in the life span of males and females in
either species. Lower temperatures (l6-20°C)
can extend the life span of both species to
approximately a year (this study; Hanlon,
1983a).
PACIFIC SCIENCE, Volume 41,1987
Octopus briareus (25 °Ck ,
Octopus bimaculoides (23 °C),
Octopus digueti (25 °C)
118
90
80
E
70
E
60
I
I-
t9 50
Z
LlJ
......J
40
LlJ
......J
I-
30
Z
«
~
20
10
5
The Pacific Pygmy OctopuS-DERuSHA, FORSYTHE, AND HANLON 119
Comparisons To Larger Octopus Species
Forsythe (I 984) concluded that O.joubini's
small size relative to larger octopus species
was not due to slower growth, but rather its
smaller hatching size and the shorter duration
of its early exponential growth phase. The
data for O. digueti further substantiate this
observation. Compared to O. bimaculoides,
O. briareus and O. maya, which grow ten times
larger in weight, O. digueti grows faster in
weight for the first 2.5 months of life (Table
6) and faster in mantle length for the first 4
months (Figure 5; no data for O. maya). How 
ever, its smaller hatching size and shorter ex 
ponential growth phase (Table 6) dictate its
smaller final size. Octopus digueti achieves
fewer doublings in weight during its shorter
exponential phase (Table 6) ending up only
one-tenth the size of the larger species. This
ten-fold difference is maintained for the re 
mainder ofthe life cycle where growth rates in
the logarithmic phase are again comparable
between species (Table 6). Interestingly, O.
digueti shows a growth regime proportionally
similar to the larger species (Table 6). Like the
larger species, it grows exponentially between
30% to 40% of its life span before slowing
slightly to a logarithmic growth phase. On this
proportional basis, O. joubini remains some 
what unusual among octopuses in having
such a short exponential growth phase, equiv 
alent to only 10% of its life span. Hapalo 
chlaena maculosa appears to have a growth
regime intermediate to O. digueti and O.
joubini based upon mantle length growth data
(Figure 5). Small octopus species clearly have
shorter life spans and therefore mature and
spawn sooner than larger species grown at
comp arable temperatures (Table 6). On a pro 
portional basis, however, differences are mini 
mal. Males begin to mature at the end of the
exponential growth phase, or about a .third
into the life cycle, and mating begins soon
thereafter. Females remain immature through 
out most of the life cycle, with the ovaries
maturing rapidly just prior to spawning (Boyle,
1983). Of the species listed in Table 6, there is
no significant difference in the life span of
males and females. The small octopus species
produce fewer and smaller eggs than large
species, but all yield benthic juveniles of similar
behavioral and locomotor ability . Although
absolute fecundity is lower, on a relative basis,
smaller species appear capable of producing
over twice as many eggs per g body weight
than larger species. The duration of embryonic
development is generally shorter in the small
octopus species, but basically represents a
comparable proportion of the life span in all
six species (Table 6).
The data available for larger octopus spe 
cies consistently show longer life spans at
comparable temperatures. The species re 
views of Boyle (I983) show life spans for
larger octopus species to range typically from
12 to 18 months. Two species, O. briareus
(maximum size 1 kg) and O. maya (maximum
size 5 kg) can have life span s as short as 10
months at high temperatures (25-30°C). Octo 
pus bimaculoides has a life span of 11 to 13
months at 23°C (Forsythe and Hanlon, 1988).
It seems that small octopus species will thus
produce more generations per year than larger
co-occurring species growing under the same
seasonal temperature constraints.
Nesis (I978) and Voight (1988) have sug 
gested that Octopus digueti and O.joubini rep 
resent a geminate species pair that diverged
from a common ancestor after the isolation of
the tropical eastern Pacific Ocean from the
Caribbean and Gulf of Mexico three to four
million years ago. The remarkable similarities
in most aspects of the biology and life history
ofO. digueti and O.joubini are consistent with
such an evolutionary premise . Future devel 
opment of genetic karyotyping methods for
cephalopods may shed some light on these
genetic relationships. Janet Voight, a grad 
uate student in the Department of Ecology
and Evolutionary Biology at the University of
Arizona, has recentl y completed a one-year
field study on the ecology of Octopus digueti at
the same site where brood stock for this lab 
oratory study were obtained. It will soon be
possible to compare the growth, reproductive
biology and life span of both field and labora 
tory populations ofthis species over the entire
life cycle.
The range of biological experimentation
that Octopus spp. have been used for (includ 
ing O. digueti) was reviewed by Hanlon and
120
Fo rsythe (1985). The general anatomical and
behavioral features of O. digueti most closely
resemble O.joubini, anothersmall species, and
the convenient culture attributes and behavior
of O. digueti render it suitable for many ofthe
types of biological experi mentation outlined
previously (ibid.).
ACKNOWLEDGMENTS
We are most grateful for funding from
DHHS grant RROl279 and from the Marine
Medicine account of The Marine Biomedical
Institute . We also thank Janet Voight for con 
structive comments on the manuscript and for
collecting the adult females for this study. The
animals were collected under permit 2999
issued by the Mexican Department of Fish 
eries to Dr. J. R. Hendrickson. We thank L. A.
Koppe for typing the manuscript.
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