Ontogeny of the digestive tract and enzymatic activity in white seabass, Atractoscion nobilis, larvae

The development of the digestive system and digestive enzyme activity in white seabass larvae, Atractoscion nobilis, were analyzed from hatching until 40 days post hatch (dph) using histological and biochemical approaches. The development of the digestive system in A. nobilis larvae was similar to that reported for other marine fish species. Larvae at 3 dph (0.55 ± 0.001 mg wet weight and 3.6 ± 0.02 mm total length), cultured at 18 °C in seawater, presented all the structures (i.e. differentiation of the alimentary canal into the buccopharynx, esophagus, anterior and posterior intestines, pancreas with zymogen granules, liver, gall bladder and open mouth) necessary for the digestion and absorption of nutrients such as proteins and lipids (primarily). At this time, the larvae had fully-developed digestive systems that allowed them to digest inert feed and to absorb nutrients throughout the intestine walls. On the other hand, most digestive enzyme activities were detected at the moment of hatching. Trypsin activity was 0.80 ± 0.16 mU/mg protein at 1 dph (0.51 ± 0.001 mg wet weight larvae), and increased gradually during the following days, but most notably after the initial exogenous feeding at 4 dph. The specific activity of chymotrypsin was 7.21 ± 1.29 mU × 10− 4/mg protein at 1 dph and reached peak level (15.9 ± 1.02 mU × 10− 4/mg protein) at 18 dph (6.6 ± 0.003 mg wet weight larvae). The specific activity of leucine aminopeptidase increased continuously from 1.31 ± 0.05 mU × 10− 3/mg protein at 1 dph to 15.91 ± 0.40 mU × 10− 3/mg protein at 18 dph. The activity of α-amylase at 1 dph was 1.35 ± 0.09 U/mg protein, increasing to 8.07 ± 0.98 U/mg protein at 16 dph. The activity of pepsin was detected at a very low level (0.71 ± 0.53 U/mg protein) at 10 dph, and a stepwise increase in activity was observed between 16 and 20 dph, reaching maximum level (13.92 ± 0.09 U/mg protein) at 40 dph. These results indicate that the digestive tract develops rapidly in this species and that the stomach becomes functional between 16 and 18 dph. It should, therefore, be possible to start weaning the fish at this young age.