The ontogenesis of digestive enzymes (proteases, amylases, lipases, and phosphatases) in Cuban gar Atractosteus tristoechus was determined in larvae between 5 and 18 days after hatching (DAH). Variations in specific activities of most enzymes were related to the transition from endogenous to exogenous feeding and to the transition from the larval to the juvenile stage. Alkaline protease activity was not detected until 8 DAH in contrast to acid protease activity, which was quantifiable at 5 DAH. Acid protease activity was consistently higher than alkaline protease activity, indicating the presence of a functional stomach in the early stages of larval development.The acid protease activities of larvae and adults were compared by means of zymogram analysis. Four acid protease bands were found in adults (two more than in larvae). This result is the first time that more than one band of acid proteolytic activity has been found in Lepisosteidae. High lipase activity indicated the importance of lipid utilization, particularly during yolk-sac absorption. In contrast to the other enzymes studied, amylase activity was consistently low, probably due to the strictly carnivorous diet of gar larvae and their low capacity for carbohydrate digestion. High activities of aminopeptidase and acid and alkaline phosphatases suggest intestinal absorption. This result, together with the existence of a short gut and a lower proteolytic activity in the intestine than in the stomach, suggest that most of the proteolytic activity takes place in the stomach, while the primary function of the intestine is nutrient uptake.

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Detailed examination of early development and growth of Cuban gar (Atractosteus tristoechus) was conducted using morphologic and morphometric characters. Larvae were reared at a constant water temperature (28 ± 1°C) from hatching to 18 days after hatching (DAH). Observation of the disappearance, reduction, or appearance of external structures, pigment characteristics, and behavior, identified three developmental stages (attached 0-3 DAH; transitional 4-10 DAH; and free-swimming 11-18 DAH). For the 18 day trial, the average growth rate was 1.30 mm/d and the specific growth rate averaged 10.2%/d. The slowest growth rates (0.02 mm/d and 2.8%/d, 7-11 DAH) coincided with the exhaustion of yolk reserves and the transition from endogenous to exogenous feeding. In addition to the slowest growth rates, the most dramatic morphological changes in A. tristoechus were observed during the transition from endogenous to exogenous feeding. Five total length (TL) groupings were established using 25 morphologic and morphometic characters. The characters snout length, pelvic fin length, snout width at nares, head length, and head width best identified length groupings. As the larvae developed, the snout and head lengthened and narrowed. Proportionally, the snout was narrower and the head longer in Cuban gar larvae than in other lepisosteid larvae.

The embryonic development of Cuban gar (Atractosteus tristoechus) was described under controlled laboratory conditions. During the whole embryogenesis seven periods were defined: the zygote (0-½ h), cleavage (¾-4 h), blastula (5-10 h), gastrula (12-20 h), segmentation (24-40 h), pharyngula (48-66 h) and hatching (72-96 h) periods. The stages were based on morphological features, generally readily identified by examination of the embryo with the dissecting stereomicroscope. Hatching occurred 96 ± 4 h after spawning at 28°C.