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The work compares the characteristics of milt produced by diploid and triploid Atlantic cod in terms of sperm motility, density, DNA content, seminal‐fluid composition and the ability of sperm to fertilize the eggs. The mean track velocity (VCL) was higher in the sperm of diploid than in the triploid males at 20 s post‐activation (p.a.; 124.04 ± 6.91 vs. 113.32 ± 6.32 μm s−1), but not at 40 s p.a. No differences between ploidies were observed for the remaining sperm‐motility descriptors as for spermatozoa density, spermatocrit or seminal fluid's variables like pH, osmolarity, Cl−, Na+, Ca2+ and K+ concentration. Triploid males produced aneuploid sperm cells (average 1.46n, range 1.2–1.6n) and the larvae generated from artificial crossings with diploid females showed abnormal morphology and did not survive to exogenous feeding. Plasma concentration of 11‐ketotestosterone in sexually mature diploid and triploid males was similar (5.35 ± 1.54 vs. 4.82 ± 1.15 ng mL−1) and no differences were found in the ability of males of both ploidies to induce spawning when held in tanks with diploid females. The paper provides evidence of gametic sterility of triploid males and examines the use of triploid fish as a management option to address the issues of genetic containment of farmed cod alongside measures for securing present fish‐farming technologies.

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Increasing anthropogenic activities in the Arctic represent an enhanced threat for oil pollution in a marine environment that is already at risk from climate warming. In particular, this applies to species with free-living pelagic larvae that aggregate in surface waters and under the sea ice where hydrocarbons are likely to remain for extended periods of time due to low temperatures. We exposed the positively buoyant eggs of polar cod (Boreogadus saida), an arctic keystone species, to realistic concentrations of a crude oil water-soluble fraction (WSF), mimicking exposure of eggs aggregating under the ice to oil WSF leaking from brine channels following encapsulation in ice. Total hydrocarbon and polycyclic aromatic hydrocarbon levels were in the ng/L range, with most exposure concentrations below the limits of detection throughout the experiment for all treatments. The proportion of viable, free-swimming larvae decreased significantly with dose and showed increases in the incidence and severity of spine curvature, yolk sac alterations and a reduction in spine length. These effects are expected to compromise the motility, feeding capacity, and predator avoidance during critical early life stages for this important species. Our results imply that the viability and fitness of polar cod early life stages is significantly reduced when exposed to extremely low and environmentally realistic levels of aqueous hydrocarbons, which may have important implications for arctic food web dynamics and ecosystem functioning.