Training of Trainers - Library - Network of Aquaculture Centres in ...

Stress brought about by the capture and holding of broodfish under controlled conditions can affect broodstockreproductive performance and eventually seed quality, thus, broodfish should be kept at low density withsufficient food.c. Reduction of the likelihood of pathogen transfer from the environment and broodstock to seedby:a. Screening of broodstock for bacteria and viruses which can be transferred betweenbroodstock and eggs.b. Isolation of hatchery stocks and location of hatcheries to reduce risk of cross-contaminationby infected and/or feral organisms and/or water sources.c. Disinfection, pre-treatment and recycling of water and quarantine before transfers are all inregular use as disease-prevention methods.d. Development of domesticated stocks that are genetically improved and are free of specificallylisted pathogens (Argue et al., 2002).d. Induction of spawning at optimal periodDue to the requirement of aquaculture producers for seed all-year-round, production of seed outsideof natural seasons have been induced but this also has implications for the quality of seed produced.For example, spawns from early and late-season batches of hybrid catfish (Clarias macrocephalus xC. gariepinus) and carp seed are known to be of poorer quality than those from the main season. Thisvariability has been explained by incomplete maturation and the onset of atresia (Ingthamjitr, 1997).e. Maintenance of genetic qualityInbreeding is a major genetic problem in captive hatchery stocks and it is often identified as a majorcause of quality deterioration. To keep inbreeding rates low (about 1% per generation), a minimum of50 pairs of breeders should be selected and the number of progeny tested should be restricted andstandardized to not less than 30–50 progeny per pair (Bentsen and Olesen (2002).Appropriate larviculture techniquesAnother major cause of poor seed quality is the lack of appropriate techniques for larviculture. Research studieshave provided useful information for the development of appropriate larviculture techniques such as:• Use of microalgae, the rotifer (Brachionus plicatilis) and the brine shrimp (Artemia) as initial feedespecially for marine species of finfish, crustaceans, and mollusks.• Use of algal substitutes in shrimp larviculture and are a key part of ‘green water’ technology used even forcarnivorous fish species. Although the algae do not constitute the major food source for these fish, thisapproach appears to improve results, probably for a variety of reasons (Lavens et al., 1995).• Enrichment of live larval feeds either indirectly by enriching the microalgae themselves or directly byraising rotifers or Artemia on enriched artificial diets. The basis of enrichment is the use of (n-3) HUFA,and especially the correct balance of EPA and DHA. Fish seed produced using these diets show bettersurvival and tolerance of stress.Effective networking and seed transportation130