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The diversification of marine finfish aquaculture has identified a requirement for live foods other than the traditional rotifer and brine shrimp species. As copepods constitute a natural component of the diets of larval fish, three species were isolated and their life cycle, environmental tolerances, and productivities investigated. Preliminary trials were also conducted feeding them to larval finfish. The temperate harpacticoid Tisbe species and the tropical cyclopoid Apocyclops dengizicus were chosen for these trials as a result of their persistence in aquaculture environs and apparent tolerance of a wide range of environmental conditions. Both Tisbe sp. and A. dengizicus populations in culture were found to tolerate temperatures and salinities over the ranges of 10 °C to 35 °C and 25 %o to 70 %o respectively, and were well accepted by first feeding larvae of test fish species. Tisbe sp. populations maintained at 20 °C and 35%0 and fed a mixed algal diet of Tetraselmis sp. and Isochrysis galbana at a density of 1.6x105cells mL-1 exhibited a mean generation time of 6.5 days. The maximum culture density recorded was 6,000 Tisbe U. A. dengizicus culture populations exhibited a mean generation time of 5.3 days when cultured at 29-32 °C and 25 °/00, with a maximum culture density of 4,500 individuals L-1 achieved when fed the same mixed algal diet as Tisbe sp.. Trials conducted with Tisbe sp. and larval greenback flounder (Rhombosolea tapirina) showed larvae ingested Tisbe sp. nauplii in preference to rotifers (Brachionus plicatilis) at initiation of feeding. Developing flounder larvae targeted progressively larger copepod stages consuming ovigerous Tisbe sp. at 12 days posthatch. Barramundi (Lates calcarifer) larvae were shown to be successful predators of all Apocyclops dengizicus life stages with ovigerous A dengizicus ingested by larvae at 6 days post-hatch. Only moribund barramundi larvae were preyed on by the cyclopoid. The tropical calanoid Acartia species was selected for these trials on the basis of the reported success achieved in Thailand when larval red snapper (Lutjanus argentimaculatus) were reared on zooplankton cultures containing Acartia spp.. Acartia sp. cultures, although tolerant of temperatures and salinities between 23 °C and 35 °C and 5 % and 45 %0 respectively, exhibited an increase in numbers only when maintained at 35%0. An estimated mean generation time of seven days was observed at 30°C. The maximum culture density achieved was 1,200 individuals L-1 when Acartia sp. were fed a mixed algal diet comprising Isochrysis galbana, Rho domonas sp., Tetraselmis sp. and Heterocapsa neie in the ratio 4:2:1:0.1 providing a final algal density of 2.3x10 6 cells mL-1. Feeding trials conducted with Acartia sp. and golden snapper (Lutjanus johnii) in volumes less than 100 L proved unsuccessful, however semi-extensive trials conducted in 40 m3 tanks yielded larval survival rates of 40 % compared with less than 0.1 % achieved when rotifers were used (Schipp, Bosmans & Marshall, 1999). |
