The ontogeny of greater amberjack digestive and antioxidant defence systems under different rearing conditions: A histological and enzymatic approach

An overall synchronization of morphological and physiological ontogenetic events of the digestive and antioxidant defence systems occurred in greater amberjack (Seriola dumerili) larvae reared under intensive (INT) or semi‐intensive (MES) conditions for 30 days. The first differentiations of the digestive channel took place at 3–4 days post‐hatch (dph) (3.6–3.7 mm). Differentiation of the endocrine and exocrine pancreas begun at 4–5 dph (4.0–4.1 mm), coinciding with a decrease in carbohydrase activity from egg to the onset of exogenous feeding and the maintenance of bile salt‐activated lipase and total alkaline proteases. The first gastric glands and pepsin activity were evident at 17–20 dph (5.5–6.2 mm) in both fish groups. The appearance of pyloric caeca had a 5‐day delay in the INT compared to the MES larvae (28 versus 23 dph). Antioxidant enzyme activities decreased progressively from 7 to 30 dph in both rearing conditions. However, GPx, SOD at 7 and 18 dph, and GST activities were higher in the INT larvae. Although both larval groups did not globally differ in somatic growth and maturation of digestive function, it seems that the antioxidant defence system of MES larvae had to face less oxidative assaults, which may be attributed to lower stressful and more stable culture conditions.