Growth, bioenergetics and life-span of Octopus cyanea and Octopus maya

Van Heukelem, William F.
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University of Hawaii at Manoa
The objectives of the work undertaken were to: (1) rear Octopus cyanea and Octopus maya through all stages of the life cycle in the laboratory; (2) measure growth rates; (3) determine energy budgets; (4) examine the effects of temperature, size and age on food intake, growth, metabolism and conversion efficiency; and (5) determine life-spans of the two species. Attempts to rear O. cyanea through the planktonic stage were unsuccessful and data were obtained on feral animals in the laboratory. O. maya was reared through four generations from eggs collected at Campeche, Mexico. Animals were fed ad libitum on living crabs. Weights were recorded at I5-day intervals and food intake was quantified. Dry matter, ash and caloric content of crab and O. cyanea samples were determined. Animals grew exponentially for the first third of their benthic life, doubling their weight every 11-13 days at 22 - 27 degrees C. The exponential growth phase was followed by a period of logarithmic growth which terminated at full sexual maturity. Average maximum sizes attained by the two species were comparable (3.2 kg for O. maya and 3.6 kg for O. cyanea). O. cyanea settles from the plankton at an estimated weight of 0.3 g and attains maximum size about 10.5 months later. O. maya hatched as benthic juveniles weighing 0.1 g and grew to maximum size in about 8.5 months. Maximum size attained by both species varied from several hundred grams to several kilograms depending on food availability. Assimilation efficiency of O. cyanea was very high (95%) and independent of animal size and food ration size. Gross growth efficiency of both species averaged about 40% on a wet weight basis and was independent of size (old animals excluded) and temperature. The relationship between food intake and growth was linear in both species and showed no sign of decrease at high ration level. Material budgets indicated that on a wet weight basis, 40% of ingested food was used in growth, 55% in maintenance and 5% was not absorbed. Energy budgets on a caloric basis indicated that 60% of ingested energy was used in growth, 36% in total metabolism and 4% voided as feces. Rates of food intake, growth and metabolism were about twice as high at 30 as at 20 degrees C. Females of both species died after brooding their eggs and males died at about the same age. O. cyanea had a lifespan of 12-15 months from settlement and O. maya lived an average of 10 months from hatching in the laboratory. Low light intensity and elevated temperature in the laboratory were thought to produce early spawning and hence short life-spans in laboratory animals. A theory is presented to explain large variations in size at spawning and lack of seasonality. Growth, differentiation, maturation and spawning are viewed as programmed events in the life cycle. Light, temperature and food determine the rate at which the program runs and hence size and age at spawning. Senescence and death are viewed as events occurring after the program is completed.
Van Heukelem, William F. Growth, bioenergetics and life-span of Octopus cyanea and Octopus maya. Honolulu (HI): University of Hawaii at Manoa, 1976.
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