Effects of different incubation and start-feeding temperature regimes on growth, survival, and histomorphology of cod larvae

Mean lengths of newly hatched cod larvae from egg incubation at 4 °C (Low-L) and 9.5 °C (High-H) were similar, and only minor differences were observed in larval histomorphology. However, growth performance of larvae reared at 4 °C (T1-LL) and 9.5 °C (T2-LH) from the 4 °C egg incubation and 4 °C (T3-HL) and 9.5 °C (T4-HH) from the 9.5 °C incubation group were different during start-feeding and metamorphosis. Incubation and larval rearing temperature affected developmental rate and survival. T1-LL and T2-LH larvae were larger than T4-HH larvae at sampling stage 4 (early larvae), but the differences disappeared thereafter. Larvae from T3-HL did not survive beyond stage 8 (late larvae/start metamorphosis), and survival of T1-LL larvae at the end of the experiment was very low. Larvae from T2-LH were significantly larger than larvae from T4-HH at stage 12 (end metamorphosis). Comparative studies of the histomorphology of vital organs did not reveal temperature-related differences between sampled larvae/early juveniles. Characteristic traits in the histomorphology of cod larvae at the selected developmental stages are presented. Our results show that egg incubation and subsequent larval rearing temperature affected the growth performance and survival but did not have any significant effects on the organ development and histomorphology.