Morphophysiological studies on alligator gar (Atractosteus spatula) larval development as a basis for their culture and repopulation of their natural habitats

Natural populations of alligator gar (Atractosteus spatula) have declined recently due to the effects of commercial and sport fisheries. Aquaculture represents a short-term alternative to restore natural populations, and a first step to accomplish culture of this species is the study of early life stages. Therefore, multidisciplinary research was used to describe the major morpho-physiological changes taking place during this period. The studies serve as a basis for the introduction of artificial diets for culture. A morphological study distinguished different nutritional stages, as well as external indicators of starvation. A histological approach showed the digestive tract to be completely formed 5 days after hatching (DAH), at the beginning of exogenous feeding. Throughout larval development, intestinal maturation was followed and a nutritional indicator based on the mid-gut cell height was validated. The occurrence of pepsin-like proteolytic activity was detected from five DAH, while trypsin, chimiotrypsin and aminopeptidase-like activities gradually increased from two to nine DAH. The incidence of cannibalism in culture conditions was controlled by exposure to anti-thyroid compounds (thiourea - TU) to retard snout growth. This treatment did not effect growth and allowed juveniles to feed on live prey but prevented the consumption of gar larvae of the same size. Larvae exposed to 3,3',5-triiodo-1-thyronine (T3) had faster development, a potentially advantageous characteristic for the repopulation of their natural habitat. Finally, artificial feeds were well accepted and resulted in growth rates similar to those of gar larvae that were fed natural prey. This has allowed the development of a feeding strategy that effectively reduced cannibalism and led to the production of 30 cm juveniles in four months.