Changes of digestive enzymes in totoaba (Totoaba macdonaldi Gilbert, 1890) during early ontogeny
ABSTRACT Totoaba macdonaldi is an endemic species which has been overexploited causing its population to decrease and to be cataloged as endangered. Understanding the larval period is the most critical stage in the development of marine fish farming. Our study aims to determine the changes in digestive enzyme activities during the early ontogeny of totoaba, using biochemical and electrophoretic techniques as SDS-PAGE. The results show that the acid protease had maximum activity between days 28 and 32 days post-hatching (DPH) when the Artemia was replaced by formulated food. Alkaline protease activity was detected at 2 DPH with maximal activity between 20 and 32 DPH; trypsin activity became active from 2 DPH; chymotrypsin activity increased at 6 DPH; leucine aminopeptidase activity was detected at 3 DPH, showing its maximal level at 22 DPH; carboxypeptidase A activity increased at 3 DPH; and lipase and amylase activities were detected at 2 DPH. Acid zymogram showed only one isoform (0.72 rf) from 2 DPH and increased in intensity from 8 DPH. For alkaline proteases, four isoforms were detected from yolk absorption (1 DPH), increasing to six isoforms (77.8, 47.3, 43.5, 21.0, 19.2, and 17.5 kDa) from 8 DPH onwards. Our results demonstrate that larvae of T. macdonaldi present characteristics typical of carnivore marine fish, showing the presence of alkaline digestive enzymes prematurely and the presence of offset pepsin. According to the results obtained in the present study, T. macdonaldi can be a juvenile beginning between 24 and 28 DPH, being the most appropriate day to perform replacement by artificial food.