Influence of Lighting Regime on the Sexual Maturation of Cage-Cultured Atlantic Cod (Gadus morhua L.)

摘要

The early maturation of cage cultured Atlantic cod (Gadus morhua, L.) is a concern in the development of commercial aquaculture. Photoperiod manipulation has been shown to have significant effects on delaying maturation in cod in tanks, however the results in sea cages are not clear. We are investigating the effects of continuous light on early maturation of Atlantic cod in sea cages on the south coast of Newfoundland. Two experimental groups of 2000 cod, each in two cages, were exposed to continuouslight, (LL; 24 hrs a day) from two 900 lux submerged bulbs. Control fish in two other cages received only the natural photoperiod (ML). This experiment was started at the summer solstice when the cod juveniles were 16 months old. Samples of 15-30 fish per cage were taken 5 times between June 2005 and May 2006. Experimental fish exposed to LL had lower gonadpsomatic and higher hepatosomatic indices which could be an indication of a difference in their level of maturity. Growth was significantly different for females (p=0.027), but not for males (p=0.474), between LL and NL treatments for May 2006 sample. A swimbladder abnormality found predominantly in LL fish may explain a lower overall growth rate. Our results indicate that supplying continuous lightcould be effective in delaying early maturation in Atlantic cod in sea cages.