Browsing by Author "Quinitio, E. T."
ArticleThe potential for stock enhancement by release of hatchery-reared juveniles continues to be a topic of interest to researchers and fisheries managers. While, in many studies, the focus has tended to be on the technology for production of juveniles, the need for a more multidisciplinary approach is now becoming accepted. Ideally, this includes studies of population dynamics and recruitment-limitation of wild stocks, environment–stock interactions, habitat availability, genetic studies of wild and released stocks and integration with appropriate fisheries management. While it may be relatively straightforward to culture large numbers of seed animals, the quality of hatchery-reared juveniles may limit the effectiveness of any release programme. The quality of juveniles may be defined either by their ability to attain the age and size to recruit to a commercial fishery or their fitness to survive to contribute to the spawning stock. Many factors will inevitably influence batch–batch variability in the viability of hatchery-reared juveniles and their ability to recruit and compete in the wild. Some effects of nutrition and environment in the hatchery are well-known or at least recognised and their manipulation offers the potential for improvement of survivorship of juveniles post-release. The choice and utilisation of broodstock also represent a crucial stage in enhancement programmes, and considerations of bottleneck effects arising from reduced effective population size due to skewed parental and family contributions must be given careful consideration. A broodstock design that encompasses sufficient numbers of animals that reflect the genetic, and preferably ecological, identity of the stocks to be enhanced should be adopted. In addition, environmental conditions and husbandry practices within the hatchery as well as broodstock and larval nutrition can all influence the quality of offspring. Further conditioning and/or selection during nursery culture may also be critical in maximising the physiological and behavioural fitness of hatchery juveniles post-release. Although evaluation of long-term performance of individual batches of juveniles requires considerable effort or may be impossible in some cases, this type of quantification is likely to be an important component in the determination of the effectiveness of release programmes. This paper reviews the effects of hatchery and nursery practice on larval and juvenile fitness for stock enhancement and presents examples of comparisons of the quality of wild and hatchery-reared juveniles and the effect of pre-release conditioning on subsequent survival and growth.
ArticleET Quinitio, FD Parado-Estepa, OM Millamena, E Rodriguez & E Borlongan -
Asian Fisheries Science, 2001 - Asian Fisheries SocietyA 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.
ArticlePercent mortality of mud crab Scylla serrata zoeae was determined after 6 h of simulated transport at mobile and stationary conditions at loading densities of 10, 20, 30 and 40 x 103 ind-l-1. Mortality was not significantly different among treatments immediately after transport. Surviving zoeae were stocked in basins, fed with Brachionus rotundiformis and mortality was compared 15 h after transport. There was no significant interaction between loading density and condition (mobile and stationary) of transport (P > 0.05). However, larval mortality varied significantly among densities (P < 0.001) regardless of the condition. A density of 10 x 103 ind-l-1 had the lowest mortality (0.56 ± 0.76%) followed by 20 x 103 (1.28 ± 0.39%), 30 x 103 (4.3 ± 0.25%), and 40 x 103 (4.3 ± 0.31%) ind-l-1. In another experiment, the effect of transport duration was determined at a constant loading density of 10 x 103 ind-l-1 in control (not subjected to packing and transport), shaken and unshaken conditions. Zoea mortality did not differ significantly (P > 0.05) after the 6, 9, and 12 h transport. Regardless of the duration, mortality was lowest in the control (0.41 ± 0.05%) compared to those in the shaken (0.99 ± 0.13%) and unshaken (0.79 ± 0.12%) conditions. Likewise, the condition but not the duration of transport affected larval survival at 15 h post-transport. Mortality was lower in the shaken (1.92 ± 0.22%) than in the unshaken condition (2.46 ± 0.17%). Since mortality is low even at 20 x 103 ind-l-1, this can still be used to transport S. serrata zoeae for 6 h. However, loading density should be reduced to 10 x 103 ind-l-1 for transport duration up to 12 h.