Reproductive performance of hatchery-bred donkey's ear abalone, Haliotis asinina, Linne, fed natural and artificial diets

Hatchery-bred donkey's ear abalone, Haliotis asinina, Linne broodstock were given diets consisting of natural food, seaweed (SW), Gracilariopsis bailinae, D1; combination of SW and artificial diet (AD), D2; and AD alone, D3. Equal numbers of 1 : 1 female and male abalone were stocked in 24 units, 60 L tanks with eight replicate tanks per dietary treatment. Reproductive performance, e.g. number of spawnings, instantaneous fecundity and egg hatching rates, was monitored over 270 days. The mean number of spawnings was not significantly different among treatments. The mean instantaneous fecundity and percent hatching rates were significantly higher in abalone fed D2 or D3 compared to those given D1. Survival of abalone broodstock fed D1 was, however, significantly higher at 88% than those fed either D2 or D3 at 75%. Fatty acid analysis showed that the n-3/n-6 fatty acid ratios of abalone hepatopancreas reflected those of their diets. Mature abalone ovary had n-3/n-6 fatty acid ratio of 1.3. A higher amount of essential nutrients in the artificial diet such as protein, lipid and the highly unsaturated fatty acids, e.g. 20 : 4n-6, 20 : 5n-3, 22 : 6n-3 in abalone fed D2 or D3, may have influenced the increased reproductive performance

Requirements of juvenile marine shrimp, Penaeus monodon (Fabricius) for lysine and arginine

Feeding experiments were conducted using amino acid test diets to determine the dietary requirements of juvenile Penaeus monodon for lysine and arginine. Two sets of the test diets were prepared. The natural protein was supplied by casein and gelatin. Crystalline l-amino acids were added to provide an amino acid profile similar to shrimp muscle protein except for the test amino acid. One set of experimental diets contained graded levels of lysine at 1.18–3.28% of the diet and another set contained arginine at 0.6–3.0% of the diet. The amino acid mixture was pre-coated with carboxymethylcellulose (CMC) and diets were further bound with CMC, cornstarch, and K–carrageenan to prevent leaching losses of amino acids. Shrimp postlarvae, PL20, with mean weight of 21±0.5 mg, were randomly distributed at 10 shrimp per tank in 40-l fiberglass tanks and reared on the diets for 50–56 days. Growth, survival and feed conversion efficiency were determined at termination of feeding trials and signs of nutritional deficiency noted. Lysine and arginine requirements were determined from relationships between weight gains and dietary lysine and arginine levels as analyzed by the broken-line regression method. The requirement of juvenile P. monodon for lysine was estimated to be 2.08% of the diet or 5.2% of dietary protein while the requirement for arginine was 1.85% of the diet or 5.3% of dietary protein. This information is crucial in formulating cost-effective practical diets for juvenile tiger shrimp

Culture of Scylla serrata megalops in brackishwater ponds

Three- to five-day old hatchery-reared megalops (4.0 to 6.4 mg body weight) of the mud crab, Scylla serrata, were cultured to the juvenile stage in 20 m2 net cages installed in brackishwater nursery ponds. To establish a suitable stocking density, megalops were stocked at 10, 20, and 30 ind·m-2 in net cages. Treatments were replicated three times over time. After 30 days of culture, mean survival of juveniles ranged from 48.3 to 53.3% and did not vary significantly (P > 0.05) among the three stocking densities. Similarly, the mean final body weights of juveniles ranging from 2.91 to 3.40 g and mass weights 458.9 to 1066 g did not significantly differ among stocking densities. These results show that stocking of crab megalops directly in net cages in a brackishwater pond is feasible at any of the stocking densities tested

Seed production of mud crab Scylla serrata juveniles

A protocol for the large-scale rearing of the mud crab Scylla serrata juveniles was developed based on the results of small-scale experiments on feeding and water management. This paper also reports the success in producing the second generation (F2) crabs. Pond-reared adult S. serrata held in 10 m3 concrete tanks with sand substrates were given fish, mussel, annelids and formulated diet. The zoeae produced were stocked in 1.5 or 10 m3 tanks at 30 to 50 ind-l-1 and fed 10 to 15 Brachionus rotundiformis ml-1, 1 to 5 Artemia sauna nauplii ml-1 and 1.5 to 2.0 g shrimp larval commercial diet-m-3 day. Water was replaced daily at 30 to 50% of the total volume starting day 3. Megalops were nursed until crab stage either in tanks or in net cages installed in ponds. Crabs were fed mussel or small shrimps (Acetes sp). Hatching occurred 6 to 12 days after spawning at 26.5 to 30.5°C. A female produced 0.42 to 5.23 x 106 zoeae at a time. Mean survival rate from zoea 1 to 3- to 5-day old megalopa was 2.6 ± 0.8% and 32.8 ± 4.8% from megalopa to crab stage. The development from zoea 1 to megalopa required 16 to 18 days. Cannibalism and luminescent bacteria were identified as the major causes of mortality. Highest mortality was observed during the metamorphosis from zoea 5 to megalopa and megalopa to crab 1. First crab stage was obtained 23 to 25 days after hatching. Sorting the crabs during the nursery period minimized cannibalism. Completion of the cycle in captivity was attained in 1997 and 1999 when spawns from pond-reared crabs grew to become the second-generation broodstock. The results point to a minimum age of 7.5 to 9 months at which S. serrata hatched their eggs after rearing from zoea 1.The authors thank the Australian Centre for International Agricultural Research for providing partial funding for this project (PN 9217)

Problems associated with tank-held mud crab (Scylla spp.) broodstock

To support studies on the development of broodstock and hatchery technology for mud crabs under the genus Scylla, the SEAFDEC Aquaculture Department maintains captive broodstock in land-based tanks. Disease problems seen in broodstock after being held for three months in these tanks include shell disease due to a combination of fouling organisms and chitinoclastic bacteria, bacterial contamination of the hemolymph, parasitic infestation on the gills and shell, and loss of appendages. Shell disease was manifested as off-white and black patches on the shell, that progressed and became perforations exposing underlying tissues. The hemolymph of a significant number of newly recruited crabs harbored mixed populations of sucrose-fermenting vibrios. Pedunculate cirripedes were found in large numbers both in the gill region and on the shell, boring through and creating perforations in the latter. Nematodes and other saprophytic organisms enter the crab through these perforations. The fouling problems that affect the integrity of the shell are considered to reduce the life span and reproductive potential of captive broodstock under tank conditions; therefore, regular cleaning of the shell is recommended to minimize shell fouling