Experimental design. Larvae were reared under common abiotic conditions, with the use of five different dry feeds (A–D, Ctrl). All trials were performed in triplicate. At 20 days post-fertilization (dpf) all groups were examined for fish size (TL), survival rate and the development of skeletal abnormalities. A, C and D groups were additionally subjected to a swimming challenge test (SCT) of 4 days (20–24 dpf) duration and examined for the presence of vertebral abnormalities. Feed quantities are given in Table 1.

Main types of skeletal deformities developed in zebrafish larvae. (a) Scoliosis of the caudal-peduncle. (b) Abnormal gill cover. (b'). Magnification of the abnormal gill cover exposing the gill filaments (Gf). (c) Abnormalities of the caudal-fin skeleton, with extra formation of haemal (*) or neural (#) processes. (c'). Normal bone structure of the caudal fin. (d) Haemal lordosis. HP, haemal process; NP, neural process. Scale bars equal to 1 mm.

Effect of starter diets on the frequency of the main skeletal deformities observed in zebrafish at the end of larval rearing period (50 larvae per replicate, 3 replicates per diet, 18–20 dpf). (a) Scoliosis of the caudal-peduncle. (b) Gill-cover abnormalities. (c) Abnormalities of the caudal complex. (d) Prehaemal kyphosis. (e) Haemal lordosis. (f) Miscellaneous vertebral abnormalities. (g) Jaw abnormalities. Different letters indicate significant differences (p < .05, G-test). Error bars equal to 1 SD.

Effect of starter diets on the frequency of vertebral abnormalities in zebrafish, following a 4-day swimming challenge test (20 individuals per replicate, 3 replicates per diet). (a) Total abnormalities of the vertebral column. (b) Haemal lordosis. The dark area indicates the frequency of fish with additional development of caudal-peduncle scoliosis. (c) Caudal-peduncle scoliosis. Different letters indicate significant differences (p < .05, G-test). Error bars equal to 1 SD.

Effect of starter diets on the mean survival (a) and total length (b) 50 larvae per diet per replicate) of zebrafish at the end of larval rearing period (18–20 dpf). Rep1-Rep3, Replicate 1–3, respectively. Different letters indicate significant differences (p < .05, Kruskal–Wallis and Mann–Whitney tests). Error bars equal to 1 SD.