The development of digestive enzymes during the early ontogeny of the Mayan cichlid (Cichlasoma urophthalmus) was studied using biochemical and electrophoretic techniques. From yolk absorption (6 days after hatching: dah), larvae were fed Artemia nauplii until 15 dah, afterward they were fed with commercial microparticulated trout food (45% protein and 16% lipids) from 16 to 60 dah. Several samples were collected including yolk-sac larvae (considered as day 1 after hatching) and specimens up to 60 dah. Most digestive enzymes were present from yolk absorption (5-6 dah), except for the specific acid proteases activity (pepsin-like), which increase rapidly from 8 dah up to 20 dah. Three alkaline proteases isoforms (24.0, 24.8, 84.5 kDa) were detected at 8 dah using SDS-PAGE zymogram, corresponding to trypsin, chymotrypsin and probably leucine aminopeptidase enzymes, and only one isoform was detected (relative electromobility, Rf = 0.54) for acid proteases (pepsin-like) from 3 dah onwards using PAGE zymogram. We concluded that C. urophthamus is a precocious fish with a great capacity to digest all kinds of food items, including artificial diets provided from 13 dah.

Changes in digestive enzyme activity and histology were studied in Atractosteus tropicus embryos, larvae and juvenile periods. Alkaline protease, chymotrypsin, carboxypeptidase A, lipase and α-amylase were detected in all periods and gradually increased until reaching the maximum peak in juveniles; meanwhile, acid protease was first detected at 5 days after hatching (dah) when first feeding started and trypsin and leucine aminopeptidase activities were detected from 19 dah, their values being increased gradually until reaching a maximum value at 31 dah. Acid and alkaline phosphatase activities increased from yolk-sac absorption (3 dah) until day 31 after hatching. Zymogram for acid protease showed two bands in active forms (0.4 and 0.5 Rfs) from day 5 after hatching and a third protease form (0.3 Rf) that appears at 31 dah. Two active forms (26.3 and 24.9 kDa) were detected using SDS-PAGE alkaline proteases zymogram at 5 dah, and an additional active form (44.1 kDa) was detected at 7 dah. Regarding the histological development of the digestive system, the exocrine pancreas containing zymogen granules was already visible at 3 dah, whereas at 5 dah first gastric glands were already detected in the stomach. Between 7 and 9 dah, the digestive tract of A. tropicus resembled that of a juvenile specimen with a well-developed and short oesophagus, stomach divided into a glandular and non-glandular (pyloric) stomach, folded intestine with pyloric caeca and a well-developed spiral valve (posterior intestine). Considering this, larvae of A. tropicus are capable of digesting several foods from yolk absorption (3 dah), maximizing its activities at 15 dah, age at which the organisms maximize its capability to absorb nutrients from diets provided.

Common snook (Centropomus undecimalis) is one of the most important marine species under commercial exploitation in the Gulf of Mexico; for this reason, interest in developing its culture is a priority. However, larviculture remains as the main bottleneck for massive production. In this sense, our objective was to determine the changes of digestive enzymes activities using biochemical and electrophoretic techniques during 36 days of Common snook larviculture fed with live preys (microalgae, rotifers, and Artemia). During larviculture, all digestive enzymatic activities were detected with low values since yolk absorption, 2 days after hatching (dah) onwards. However, the maximum values for alkaline protease (6,500 U mg protein(-1)), trypsin (0.053 mU × 10(-3) mg protein(-1)), and Leucine aminopeptidase (1.4 × 10(-3) mU mg protein(-1)) were detected at 12 dah; for chymotrypsin at 25 dah (3.8 × 10(-3) mU mg protein(-1)), for carboxypeptidase A (280 mU mg protein(-1)) and lipase at 36 dah (480 U mg protein(-1)), for α-amylase at 7 dah (1.5 U mg protein(-1)), for acid phosphatases at 34 dah (5.5 U mg protein(-1)), and finally for alkaline phosphatase at 25 dah (70 U mg protein(-1)). The alkaline protease zymogram showed two active bands, the first (26.3 kDa) at 25 dah onwards, and the second (51.6 kDa) at 36 dah. The acid protease zymogram showed two bands (RF = 0.32 and 0.51, respectively) at 34 dah. The digestive enzymatic ontogeny of C. undecimalis is very similar to other strictly marine carnivorous fish, and we suggest that weaning process should be started at 34 dah.

In bay snook (Petenia splendida) larvae the histological development of the digestive system and swim bladder, and their relative timing of differentiation were studied from hatching to 45 days post-hatch (dph) at 29°C. Newly hatched larvae showed a simple digestive tract, which appeared as a straight undifferentiated tube lined by a single layer of columnar epithelial cells (future enterocytes). The anatomical and histological differentiation of the digestive tract and accessory glands was a very intense, asynchronous process, proceeding from the distal to the anterior part. The intestine was the first region to differentiate (9 days post-hatch -dph, 6.5 mm SL), and the oesophagus the last (21 dph, 8.4 mm SL). At the onset of feeding, the digestive system was organized into different functional and histologically differentiated sections, such as the buccopharynx, oesophagus, glandular stomach, and anterior and posterior intestine. This organization resembled that of the juveniles, with the exception of pharyngeal teeth and buccopharyngeal as well as oesophageal goblet cells, which proliferated later during the mixed feeding period. Histological observations revealed that bay snook larvae retained endogenous yolk reserves until 24 dph (8.9 ± 0.4 mm SL), which might be helpful for weaning this species onto a compound diet. The important lipidic accumulation observed in the intestinal mucosa, liver, and pancreas in fish fed a compound trout diet indicated that although fish were able to digest and absorb lipids, the diet formulation did not fit the nutritional requirements of early juveniles of this species. The ontogeny of the digestive system followed the same general pattern as in most cichlid species described to date. However, we detected species-specific differences in the timing of differentiation that were related to their reproductive guild. According to the histological results, some recommendations regarding the intensive culture of this species are also provided.

Several samples of P. splendida larvae were obtained from eggs until day 60 after hatching (dah) to determine acid and alkaline proteases, trypsin, chymotrypsin, leucine aminopeptidase, α-amylase, lipase, and acid and alkaline phosphatase activities using biochemical techniques. Additionally, SDS-PAGE alkaline protease zymogram and PAGE acid protease zymogram were carried out to identify active isoforms during larviculture. Alkaline protease and chymotrypsin were present at the moment of hatching, increased gradually reaching the maximum values at 35 dah. Trypsin and leucine aminopeptidase activities were low from hatching, increasing gradually as larvae grew. Alkaline protease zymogram showed four zymogens, which appears at different days, remaining present until the end of the larviculture (95.2 kDa at 11 dah, 26.4 kDa at 9 dah, 21.4 kDa at 3 dah, and 23.3 kDa at hatching). Pepsin activity was present at day 7 after hatching and increased progressively until the end of the larviculture. Acid protease zymogram only showed one zymogen (0.65 rf), which appear at 6 dah. Lipase was high at the time of hatching and increased until 15 dah, after which decreased gradually. Amylase was high from the beginning and until 15 dah and then decreased rapidly to almost nothing onward. Alkaline and acid phosphatases presented a high activity at the egg stage, fell slightly during the first feeding and increased again from 20 to 30 dah. Results obtained in this study show that larvae can be fed artificial diets starting on day 10 after hatching.