Gonadal development influences nutrient utilisation in cod ( Gadus morhua)

Abstract

The present paper elucidates how various light regimes influence nutrients utilisation and retention during gonadal maturation in Atlantic cod ( Gadus morhua). Details from the same study on population growth, gonadal development and spawning time are published by [Aquaculture 203 (2001) 51.]. During the first year, photoperiod treatments were natural light (LDN), continuous light (LL), natural light from June and continuous light from December until next June (LDN/LL), and continuous light from June and thereafter natural light from December until next June (LL/LDN). All groups were fed the same diet. There were small differences in feed conversion ratio (FCR) between groups during the first 6-month period of the experiment (June to December). In the following 6 months, FCR was highly influenced by the differences in rate and pattern of sexual maturation. The FCR was slightly higher in the LL/LDN than the LL group in this period. However, the LL/LDN group was in the middle of their spawning season when sampled in June and the spawning effect on FCR was therefore only partly realised. The low FCR of the LL group reflects that cod subjected to continuous light did not mature during the experimental period. The sexually maturing groups showed tendencies to anemia, with reduced blood hemoglobine (HB) concentration and reduced red blood cell count (RBC). The investment in gonads resulted in reduced concentrations in plasma cholesterol, triacylglycerols (TAG) and glucose, but it did not affect plasma total protein concentrations. Whole body dry matter was reduced almost linearly as gonads increased, without any correlation towards whole body lipid, but strongly correlated to reduced whole body protein levels. Cod subjected to regimes LL and LL/LDN showed significant postponed spawning. For these groups, no detectable variations in protein retention, blood, plasma or whole body compositions were found.