Early Nutrition Impacts on Growth, Skeletal Anomalies and Organ Ontogeny in Larval Atlantic Cod (Gadus morhua)

Early life nutrition is a critical factor influencing subsequent performance and quality, including skeletal development, in farmed Atlantic cod (<i>Gadus morhua</i>). This study investigated the effects of a novel start-feed protocol utilizing barnacle nauplii and plankton eggs and two experimental microdiets on larval survival, growth, skeletal anomalies, and organ ontogeny. Atlantic cod larvae were reared using three feeding protocols (COM, D1, and D2): COM used enriched rotifers and a commercial microdiet, while D1 and D2 protocols incorporated blue mussel eggs (Cryo-µ) and barnacle nauplii (Cryo-S, Cryo-L), followed by inert microdiets that differed in their phospholipid (PL) source (D1 richer in vegetable PL; D2 richer in marine PL). Larvae were sampled up to 66 days post hatching (dph) for morphometric, skeletal anomaly, and histological analyses. Survival averaged 21.3% and was unaffected by the diets. The control group had slightly higher standard length and dry weight at 66 dph compared to the experimental groups. However, larvae fed the D1 protocol exhibited a significantly lower overall prevalence of skeletal anomalies (52%) compared to the control group (91%). Moreover, D1 showed a lower occurrence of severe anomalies and a significantly reduced prevalence of scoliosis compared to both D2 and COM groups. Histology showed that group D1 achieved an overall accelerated organ ontogeny, with greater villi length and goblet cell abundance in the anterior intestine at 66 dph. In conclusion, the novel D1 feeding protocol, incorporating barnacle nauplii and a microdiet richer in vegetable phospholipids, enhanced larval quality by effectively reducing skeletal anomalies and accelerating internal organ development.