Competitive Spawning of Male Triploid Atlantic Cod (Gadus morhua) and the Early Life History Performance of their Offspring

No abstracts are to be cited without prior reference to the author.

Farmed Atlantic cod (Gadus morhua) escaping or spawning directly in sea cages poses a continuous risk to the natural environment, similar to that recognized for the salmon aquaculture industry. Cod culture is in its infancy, providing the industry and scientific community the opportunity to develop cod culture in an environmentally sound and profitable manner. Preliminary research has shown that triploid females do not produce hydrated oocytes, while male triploids undergo spermatogenesis. Although this precludes the opportunity for within-cage mating of triploid females and males, it does pose a possible problem if male triploids were to escape. The purpose of this study was to examine if male triploid Atlantic cod are capable of outcompeting male diploids for spawning access to female partners, and to evaluate the viability of their offspring. Fertilization rates, daily embryonic survival, hatch rates and daily, unfed larval survival were compared by manually fertilizing eggs with sperm from males of each ploidy. Data were collected from ten replicate trios, with each trio comprised of a male of each ploidy and a diploid female. No significant difference was found between fertilization rates using milt stripped from triploids and diploids. A significant difference was found for hatch rates and survival, with offspring from diploid males being superior to those of triploids. Trios of fish were also placed in eight tanks and permitted to undergo spawning to determine whether a triploid male was able to gain access to a female in a competition setting with a diploid male. Egg batches were collected from tanks and microsatellite DNA makers used to determine proportion of embryos sired by each male.