Early Weaning Effects on Survival, Growth, and Histopathology of Larval Sterlet Acipenser ruthenus

Weaning of fish is a critical stage during larval rearing and could cause high mortality. Therefore, proper larval weaning period selection is crucial for the success of larviculture. This study aimed to find the effect of weaning on growth performance, histopathological features, and mortality rates in larvae of Sterlet Acipenser ruthenus. The experimental rearing was conducted from 7 to 38 d posthatch (dph) at a mean temperature of 18°C in a recirculating system. The experiment was carried out in three groups (each with three replicates) and placed in nine tanks (22 L) at a density of 10 individuals/L. The diet groups were made up of group C in which larvae were fed with nauplii of brine shrimp Artemia spp., group F7 in which larvae were weaned to dry feed 15 dph, and group F that was fed with dry feed throughout the experimental trial. During 15–38 dph, total wet body weight and total length were lowest in the group fed with formulated feed. Survival rate of larvae in group F7 was 90.45% and 70.05% during 7–14 and 15–22 dph, respectively. On the other hand, the survival rate of larvae fed only Artemia nauplii (group C) or formulated feed (group F) was 86.14% and 70.45% during 7–14 dph and 84.55% and 78.41% during 15–22 dph, respectively. The maximum height of the enterocytic epithelium was found in the individuals in group F7 (mean ± SD = 33.80 ± 2.56 μm). The average height of enterocytes of group F7 (n =30 fish) larvae were significantly increased at 15, 23, and 38 dph compared with the larvae fed with formulated feed and live feed, but no significant changes were observed in the liver cells, including in the diameter of hepatocytes and their nuclei. This study provides evidence that Sterlet larvae should be fed with Artemia nauplii at 7–15 dph because fish gain a higher wet body weight and total length and develop a better liver and digestive tract.