Balancing between Artemia and microdiet usage for normal skeletal development in zebrafish (Danio rerio)

The role of starter diets in the development of skeletal abnormalities in zebrafish Danio rerio (Hamilton, 1822)

Fish skeletal development has long been correlated with nutritional factors. Lack of zebrafish nutritional standardization, especially during the early stages, decreases the reproducibility of the conducted research. The present study represents an evaluation of four commercial (A, D, zebrafish specific; B, generic for freshwater larvae; C, specific for marine fish larvae) and one experimental (Ctrl) early diets on zebrafish skeletal development. Skeletal abnormalities rates in the different experimental groups were assessed at the end of the larval period (20 days post-fertilization, dpf) and after a swimming challenge test (SCT, 20-24 dpf). At 20 dpf, results revealed a significant effect of diet on the rate of caudal-peduncle scoliosis and gill-cover abnormalities, which were relatively elevated in B and C groups. SCT results focused on swimming-induced lordosis, which was comparatively elevated in diets C and D (83% ± 7% and 75% ± 10%, respectively, vs. 52% ± 18% in diet A). No significant effects of dry diets were observed on the survival and growth rate of zebrafish. Results are discussed with respect to the deferential diet composition between the groups and the species requirements. A potential nutritional control of haemal lordosis in finfish aquaculture is suggested.

Effect of Early Peptide Diets on Zebrafish Skeletal Development

Incorporation of dietary peptides has been correlated with decreased presence of skeletal abnormalities in marine larvae. In an attempt to clarify the effect of smaller protein fractions on fish larval and post-larval skeleton, we designed three isoenergetic diets with partial substitution of their protein content with 0% (C), 6% (P6) and 12% (P12) shrimp di- and tripeptides. Experimental diets were tested in zebrafish under two regimes, with inclusion (ADF-Artemia and dry feed) or lack (DF-dry feed only) of live food. Results at the end of metamorphosis highlight the beneficial effect of P12 on growth, survival and early skeletal quality when dry diets are provided from first feeding (DF). Exclusive feeding with P12 also increased the musculoskeletal resistance of the post-larval skeleton against the swimming challenge test (SCT). On the contrary, Artemia inclusion (ADF) overruled any peptide effect in total fish performance. Given the unknown species' larval nutrient requirements, a 12% dietary peptide incorporation is proposed for successful rearing without live food. A potential nutritional control of the larval and post-larval skeletal development even in aquaculture species is suggested. Limitations of the current molecular analysis are discussed to enable the future identification of the peptide-driven regulatory pathways.

Variability of key-performance-indicators in commercial gilthead seabream hatcheries

Skeletal abnormalities are one of the most important key-performance-indicators (KPIs) in finfish hatcheries. Coping with the problem of skeletal abnormalities relies on the understanding of the link between the variability in the rearing conditions, and the variability in abnormalities incidence. Here, 74 seabream larval populations, from four commercial hatcheries, were examined for the presence of abnormalities and monitored with respect to the applied conditions. The inward folding of gill-cover and pugheadedness were the most frequent abnormalities present, with a mean (± SD) frequency of 11.3 ± 17.9 and 6.0 ± 7.2%, respectively. Other abnormalities were observed at very low mean rates (≤ 1%). A new abnormality type, ray-resorption syndrome, was also found. The recorded rate of normally inflated swimbladder was 92.3 ± 7.4% and mean survival rate was 25.9 ± 21.0%. Classification tree analysis indicated six rearing variables as potentially important predictors for pugheadedness, six variables for caudal-fin abnormalities and 10 variables for survival rate. Complementary genetic analysis, revealed differentiating genetic diversity and significant genetic distances among participating hatcheries, suggestive of the role of company-specific management of genetic resources in KPIs' variability. The results are discussed with respect to their potential use in the control of skeletal abnormalities by commercial hatcheries, as well as for benchmarking among different hatcheries.