The sea louse, Lepeophtheirus salmonis, is parasitic to salmonid species in the Northern Hemisphere and has become a widespread biological and economic problem for the salmon farming industry. A better understanding is needed of their spatial distribution and early life history to disrupt the life cycle of the sea louse. In this study, sea lice larval densities within salmon farms, between salmon farms and reference sites, and at various depths were quantified using both plankton pumps and plankton nets. Farm sites exhibited significantly higher densities than reference sites; however, these densities dropped an order of magnitude at a distance of 100 m from the cages. The majority of the larvae captured in the study were nauplii (93%), and densities ranged from 0 to 10 larvae/m . Free-swimming sea lice larvae were found to exhibit a diel cycle where nauplii larvae were in deeper waters (10-17 m) during the day and in surface waters (1-6 m) during the night. The results of this study suggest that the early life-history stages of sea lice originate from and may remain close to active salmon farms, creating a self-sustaining population.

Farmed Atlantic cod Gadus morhua have been hypothesized to pose a risk to the natural environment through escape of fish or release of their gametes from sea cages. The use of sterile triploids has been suggested as a way to prevent spawning of farmed fish, whether escaped from their cages or still contained within them. This laboratory study examined the reproductive potential of triploid male Atlantic cod, both in vivo and in vitro. We demonstrated that triploid males in competitive, size-matched mating with diploid males were successful at siring young. Spermatozoa produced by triploid males were larger than those of diploids, but did not differ in swimming velocity or ability to fertilize eggs. Hatch and larval survival rates, however, were reduced for progeny of triploid males. These diagnostic characteristics of aneuploidy suggest that although farmed triploid male cod may compete successfully with wild diploids for spawning access to wild females, their offspring will not survive.

During their third and fourth years of life, triploid Atlantic cod Gadus morhua females exhibited diminished ovarian development at both macroscopic and microscopic levels, with significantly lower gonado-somatic indices (I(G)) and higher carcass yields (Y(C)) than diploid females during spawning periods. In contrast, diploid and triploid testes were indistinguishable through macroscopic and histological assessment. No significant differences were found in male I(G) or Y(C) in relation to ploidy, with the exception of a higher Y(C) for triploids during the first of the two monitored spawning seasons. As a result of suppressed oogenesis, triploid female G. morhua, but not triploid males, can be used to eliminate sexual maturation in this species and advance the development of the G. morhua aquaculture industry.

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