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 recentlydue to the effects of commercial and sportfisheries. Aquaculture represents a short-termalternative to restore natural populations, anda first step to accomplish culture of thisspecies is the study of early life stages.Therefore, multidisciplinary research was usedto describe the major morpho-physiologicalchanges taking place during this period. Thestudies serve as a basis for the introductionof artificial diets for culture. Amorphological study distinguished differentnutritional stages, as well as externalindicators of starvation. A histologicalapproach showed the digestive tract to becompletely formed 5 days after hatching (DAH),at the beginning of exogenous feeding.Throughout larval development, intestinalmaturation was followed and a nutritionalindicator based on the mid-gut cell height wasvalidated. The occurrence of pepsin-likeproteolytic activity was detected from fiveDAH, while trypsin, chimiotrypsin andaminopeptidase-like activities graduallyincreased from two to nine DAH. The incidenceof cannibalism in culture conditions wascontrolled by exposure to anti-thyroidcompounds (thiourea – TU) to retard snoutgrowth. This treatment did not effect growthand allowed juveniles to feed on live prey butprevented the consumption of gar larvae of thesame size. Larvae exposed to3,3,5-triiodo-1-thyronine (T3) had fasterdevelopment, a potentially advantageouscharacteristic for the repopulation of theirnatural habitat. Finally, artificial feeds werewell accepted and resulted in growth ratessimilar to those of gar larvae that were fednatural prey. This has allowed the developmentof a feeding strategy that effectively reducedcannibalism and led to the production of 30 cmjuveniles in four months.