Feeding ecology of juvenile white shrimp, Penaeus vannamei, in intensive aquaculture ponds

Abstract

Intensive aquaculture ponds possess unique ecological characteristics that contribute substantially to shrimp growth and survival. In this dissertation, I have examined the feeding ecology of juvenile white shrimp, Penaeus vannamei, reared under intensive culture conditions, in an attempt to understand the relationship between this unique pond ecosystem and shrimp growth. Intensive shrimp ponds contain high concentrations of suspended organic particles that are rapidly assimilated by juvenile shrimp. These organic particles not only enhance growth of shrimp fed high-protein diets, but also provide adequate nutrition to sustain moderate growth in the absence of pelleted feed. Living biomass in pond water is often dominated by pennate and centric diatoms that experience a bloom and crash cycle, whereas contributions from bacteria and protozoans are minor. Growth-enhancing particles in shrimp pond water are produced in the water column, and do not need to interact with an earthen substratum to elicit their effect. To assess how rapidly shrimp responded to the presence of these growth-enhancing particles, I used nucleic acid analysis to estimate shrimp growth over short time intervals. RNA concentrations and RNA/DNA ratios can be used successfully to discriminate between negative, moderate, and rapid shrimp growth, and more than 60% of the variation in growth rate was explained by changes in either of these two variables. Furthermore, unfed shrimp reared in pond water exhibited significantly greater RNA concentrations and RNA/DNA ratios than unfed shrimp reared in clear well water, and these differences were detected less than 24 hours after the start of the experiment. Nucleic acid analysis was also used to assess the nutritional contribution of different alga to shrimp. Alga tested in this study were considered to be potential food resources for both wild and cultured penaeids. Diatoms contributed substantially to short-term shrimp growth, whereas the green algae, Nannochloropsis oculata, and the macroalga, Ulva sp. and Enteromorpha sp., did not support growth. In addition, the diatom component of pond water can account for all of the shrimp growth in the earlier pond water studies. However, it is unlikely that diatoms can support long-term shrimp growth and survival.