Effects of continuous light and triploidy on growth and sexual maturation in Atlantic cod, Gadus morhua
Early maturation is considered one of the greatest problems in mariculture of Atlantic cod. We examined two approaches to impede early puberty: (i) exposure to continuous light and (ii) induction of sterility by triploidy. Use of continuous light initiated in July delayed onset of sexual maturity, in this case by ~2-3 months though cod returned to their normal spawning period when continuous light was administered for a second year. In the first year, 24 h light compared to natural photoperiod resulted in a lower percentage of mature females (73 vs 90%) compared to males (90 vs 100%). In the second year, > 88% of any gender were mature in both treatments. Using hydrostatic pressure, triploid cod were generated with a 100% success rate at a treatment of 5 min at 58,600 kPa (8500 psi) applied beginning at 30 min post-fertilization for eggs held at 6°C. No sexually mature female triploids were observed, yet 12.5% of triploid males were mature. Female triploids grew at a slower rate than diploids, and for males triploids and diploids were not significantly different in growth (body weight at age 26 mos.). A family by ploidy interaction for growth was nearly significant (p = 0.052) which underlines the importance of conducting extensive testing of the effects of triploidy among a large number of families, perhaps coincident with a selective breeding program, if one is to thoroughly evaluate the scope of this technique in assisting the cod aquaculture industry.