Larval rearing and ontogeny of digestive enzyme activities in yellowfin seabream (Acanthopagrus latus, Houttuyn 1782)

Abstract

The present research was conducted to provide insight into digestive larval capacity in Acanthopagrus latus larvae from hatching up to 30 days after hatching (DAH). Newly hatched larvae were stocked into six 300-L cylindrical polyethylene tanks at a density of larvae 50 larvae/L and reared by means of the green water system using Nannochloropsis oculata (0.5 × 106/mL). After mouth opening, larvae were fed with rotifers (5–16 individual/mL) from 2 to 20 DAH; then, Artemia nauplii (0.5–3.0 individuals/mL) were offered to larvae from 18 to 30 DAH, meanwhile a commercial microdiet was offered to larvae from 25 to 30 DAH. Larval performance in terms of growth and survival, and the assessment of the activity of selected digestive enzymes ontogeny of digestive enzymes activities was evaluated in larvae sampled at 0 (hatching), 7, 15, 22 and 30 DAH. Larvae showed an exponential growth characterized by two different growth stanzas, a first one characterized by slow growth rates comprised between hatching to 15 DAH (4.7 ± 0.2 mm), followed by a period of faster growth rates between 16 and 30 DAH (7.5 ± 0.6 mm). The activities of the brush border (alkaline phosphatase, ALP) and cytosolic (leucine-alanine peptidase, LAP) enzymes, as well as those of the pancreatic ones like total alkaline proteases, bile salt-activated lipase and α-amylase were detected from the mouth opening stage. Total activities of pancreatic and gastric enzymes increased with larval growth showing an enhancement of digestive capacities with larval age and size. The intestinal maturation in A. latus as assessed by the ratio of AP to LAP did not occur as expected by end of the first month of life suggesting the complete establishment of digestive luminal processes may take place at older ages. This study related to the growth patterns and ontogenic changes in activity of pancreatic, gastric and intestinal enzymes in A. latus and their nutritional regulation may be considered as the first step for improving the larviculture, as well as assessing and refining the nutritional requirements during the larval and early juvenile stages of this sparid species.