Effective larval rearing protocols are essential for hatcheries to maximize production success. We currently seek to achieve consistently high larval survival (>20% from egg to 1g) and high quality fingerlings (<10% sortable deformities). Here, we evaluate the effects of different live feed types, rotifer enrichments and feeding schedules on skeletal deformities of white seabass (Atractoscion nobilis).
Two trials were conducted in 320L tanks with four replicates per treatment. Water temperature was at 18°C (± 1˚C). Tanks were stocked at a density of 45 eggs/L (Trial 1) and 40 eggs/L (Trial 2), and larvae were reared to 60 days post hatch (dph) using standard rearing practices. In both trials, an “Artemia only” (Art-only) treatment was used as the control and was compared to treatments that included both rotifers and Artemia, since A. nobilis has historically been reared by only providing Artemia during the live-feeds phase. In Trial 1, two different rotifers enrichments were tested against the Art-only treatment: (a) Rotigrow+Origreen (Rot-Ori) and (b) Rotigrow+Onestep (Rot-One). All groups received enriched 2nd instar Artemia from 5 to 35 dph. In Trial 2, rotifers were offered to larvae under different feeding schedules to evaluate the effects of delaying or extending the rotifer feeding during early development. The treatments were as follows: “Art-only” starting at 4 dph; “Standard” (rotifers from 2 to 7 dph); “Delay” (rotifers from 4 to 7 dph); and “Extend” (rotifers from 2 to 10 dph). Performance metrics for both trials included; growth, survival rate and assessment of bony deformities using standardized protocols.
Growth was significantly higher in all groups that received rotifers compared to the Art-only treatment in both trials (P < 0.05) but survival was not statistically different. In both trials, sortable malformations were observed mainly in the head region at ≥1% prevalence in one or more treatments. In Trial 1, the Art-only group had 66% sortable deformities; compared to Rot-One (14%) and Rot-Ori (8%) treatments. In Trial 2, the deformities were higher in the Art-only and Delay groups (46% and 31%, respectively), and lower in Extend and Standard groups (23% and 18%, respectively). In both trials, the overall higher prevalence of bony deformities in the Art-only treatments were largely represented by cranial protrusions and branchiostegal deformities. These results indicate that feeding enriched rotifers as early as possible and optimizing rotifer enrichments can significantly improve the early developmental success in hatchery production of white seabass. Delaying feeding can lead to higher rates of deformities. Additional research is required to identify the cause-and-effect mechanisms.