Optimized application of rotifers Brachionus plicatilis for rearing pikeperch Sander lucioperca L. larvae

Abstract

This study aimed to optimize the use of euryhaline rotifer Brachionus plicatilis for rearing larval pikeperch Sander lucioperca L. We assessed motility of rotifers under salinities of 0‰, 2‰, 4‰, 8‰, and 16‰ over a 6-h period. Rotifers stocked into freshwater were completely immotile within 2 h. The motility of rotifers after 6 h was 10 ± 2.27% at 2‰, 35 ± 5.58% at 4‰, 79 ± 30.35% at 8‰, and 92 ± 1.98% at 16‰. A second trial quantified the effect of the target salinity levels on pikeperch gut fullness over the course of 11 h. The gut fullness of larvae fed with rotifers was significantly lower at 8‰ salinity than in other tested groups. Salinity of 16‰ resulted in 100% mortality. Survival and growth of pikeperch larvae from 4 to 11 days post-hatching (DPH) was analyzed at low (2‰ and 4‰) and medium (8‰) salinity. Differences in larval performance under tested salinities were found in survival (S), total length, SGR, eye diameter, myotome height, and gut fullness. The highest mean survival (S) and specific growth rate (SGR) were obtained at 2‰ (S = 64%; SGR = 10 ± 5.4% day−1) and 4‰ (S = 65%; SGR = 8.23 ± 3.4% day−1) salinity and significantly differed from 8‰ (S = 36%; SGR = 5 ± 2.3% day−1) and control (S = 34%; SGR = 7 ± 3% day−1) at 11 DPH. At the conclusion of the trial (11 DPH), larvae of all exposures and control presented normal histology with no signs of pathology. Morphometric analyses revealed significant differences in brush border and fold height of anterior intestine among treatment groups. Larvae at 2‰ salinity showed significantly higher intestinal fold height (31.2 ± 5.40 μm) compared to those at 4‰ (26.5 ± 6.11 μm), 8‰ (26.3 ± 4.52 μm), and control (22.8 ± 5.13 μm) (p ˂ 0.05). Larvae at 4‰ salinity had significantly higher brush border height (2.50 ± 0.73 μm) compared to those at 2‰ (2.27 ± 0.63 μm) and 8‰ (1.87 ± 0.44 μm) salinity and control (1.66 ± 0.56 μm) (p < 0.05). The results showed 2‰ and 4‰ salinity supported higher numbers of motile B. plicatilis and higher larval survival and growth rate to 11 DPH.