| Summary: | This paper describes the strategy utilized for the domestication of the alligator gar(Atractosteus spatula), highlighting different aspects of larval development and theweaning of larvae onto artificial diets. Developmental stages based on nutritionalcharacteristics were established. Lecithotrophic stage was observed between 1–4 days afterhatching (DAH) larvae, lecithoexotrophic stage between 5–8 DAH larvae and theexotrophic stage initiates in 9 DAH larvae. The degree of development for alligator garlarvae could be differentiated by snout length. In addition, pigmentation could be easilyused to separate individuals in poor condition. Growth rate of alligator gar larvae was 1.55mm/day during the first 10 DAH and 5.6 mm/day thereafter until 15 DAH. RIA analysesshowed that T3 levels are low during embryonic development, but increase after hatching,until 10 DAH, decreasing thereafter. The effect of thyroidian hormones and goitrogens onlarval development was evaluated. Snout length was significantly reduced in larvae treatedwith thiourea without affecting growth, whereas in larvae treated with T3 snoutdevelopment was accelerated. Histological assessment of the development of the digestivetract revealed that at the onset of exogenous feeding (5DAH) the digestive tract wascompletely developed. Measurement of mid-gut cell height was valuable tool for evaluatingthe suitability of diets. Additionally, the ontogeny of digestive enzymes was characterized.Pepsin-like acid proteolytic activity was detected from the beginning of exogenous feeding(5 DAH). Trypsin, chymiotrypsin and aminopeptidase-like alkaline proteolytic activitygradually increased between 2-9 DAH. Substrate-gel electrophoresis was utilized toconfirm and further characterize digestive enzyme activity. Growth hormone codingsequence was obtained by RT-PCR and its expression was detected in embryos and inseveral larval stages, revealing an important role during embryogenesis and organogenesis.RNA/DNA ratios were determined and proven to be a useful indicator of larval nutritionalcondition. In fed larvae RNA/DNA ratio rose until the 13 DAH, while in starved larvae theratio RNA/DNA was low and remained constant. Three feeding experiments were carriedout and some important characteristics of artificial diets were identified, namely floatabilityand size. The results of the feeding trials made it possible to culture larvae and juvenilesusing exclusively artificial diets.
|
|---|
