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Eggs and larvae produced by pairs of spawning haddock Melanogrammus aeglefinus were monitored between 2001 and 2003 to determine the effects of spawning time, egg size and food supply on early life history success. Females usually released eggs at 3 d intervals. All females exhibited a continuous decrease in egg diameter and dry weight with consecutive batches, but the decrease in size did not influence fertilization or hatching success. Larval size (standard length and dry weight), yolk area, eye diameter, myotome height, and finfold area were all positively related to egg size and therefore decreased between early- and late-season larvae produced by the same spawning pairs. Differences in larval morphology persisted for at least the first 5 d after hatching. Jaws were not developed at hatching (5 degree C), but jaw length did show a strong positive relationship with egg size at 5 d post-hatch (dph). The ability of newly hatched larvae to withstand periods of starvation was directly related to initial egg size. Under high prey abundance (5000 l super(-1)) larval survival to 20 dph was highly variable (1.8 to 50.7%) with no differences in survivorship or specific growth rate (0.818 to 0.936% d super(-1) in standard length) for larvae from early-, middle- and late-season egg batches. With low prey density (1000 l super(-1)) survival of larvae from late-season egg batches was significantly lower (0.4%) than those from early egg batches (1.8%). No differences in larval specific growth rate existed between early and late batches, but growth rate was reduced in both cases with low food abundance (0.683 to 0.690 d super(-1) in standard length). Results suggest that smaller larvae produced late in the spawning season have reduced feeding capabilities and may experience lower survivorship in the ocean than larger, early-season larvae.

Biological processes related to reproduction in northwest Atlantic groundfish populations that have undergone declines are reviewed. Use of age at maturity as an indicator of changes in population size holds promise.

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.

Fish often escape from aquaculture operations, raising concerns of interactions with wild individuals. Farmed fish from genetically diverse populations grown outside their native range create the threat of outbreeding depression if they escape and interbreed with wild fish. Atlantic cod Gadus morhua spawn within cages, releasing millions of embryos into the environment, some of which may live to reproduce. Due to selective breeding, fewer breeding individuals are used in culture relative to wild populations, potentially leading to inbreeding within single cages. If inbreeding reduces survival, this could reduce the likelihood of outbreeding depression if maturing escaped cod mate with wild cod. Forced inbreeding could be used to mitigate some effects of aquaculture on the environment. We aimed to determine if cod inbreed and, if so, what short-term effects inbreeding has on offspring. Spawned embryos from tanks of sister−brother−unrelated male trios underwent microsatellite analysis to determine parentage. Inbreeding occurred, and females did not prefer one type of male over the other. Percent hatch, deformities, larval size, and mortality were monitored in artificially fertilized inbred and unrelated crosses. Percent hatch was higher in non-inbred offspring, but inbreeding had no significant effect on the other factors.

Egg and larval production of 22 captive spawning pairs of northwest Atlantic haddock (Melanogrammus aeglefinus) were monitored. Females spawned an average of nine egg batches (range 3–16) with a mean batch fecundity of 60 000 eggs and mean total fecundity of 535 000 eggs. Mean spawning duration was 37 days with a mean batch interval of 5.4 days. In multiple linear regression, male Fulton's condition factor (range 1.10–1.55) and mean batch interval explained 56% of variation in fertilization rate (33% and 23%, respectively). Seasonal composite egg diameter spanned 1.37–1.53 mm among females. Mean egg diameter within females declined seasonally by an average of 10.4% (37% by volume). Females produced 46 larvae per gram body weight. Body weight was the single best predictor of fecundity (r 2 = 0.57), with Fulton's condition factor (range 1.04–1.76) explaining no significant additional variation over length or weight. Length and condition explained 39% of variation in seasonal composite egg diameter (22% and 17%, respectively) and body weight independently explained 32%. Sex-specific parental condition and body size acted through large egg size and elevated fertility to enhance reproductive output. Male spawning success was more sensitive than egg production to changes in condition.

Embryo survival, larval standard length, yolk-sac area, yolk utilization and resistance to starvation were significantly influenced by the female parent and the interaction between both parents of Baltic Sea cod Gadus morhua in a gamete factorial cross of 3 females and 5 males in all possible combinations. The proportion of variance in embryonic survivorship that was due to maternity during incubation was significant during the first 4 d, but was insignificant during the 5 to 9 d interval. During the 5 to 9 d interval, the male-female interaction was significant. Standard lengths at hatch and 5 d post hatch and specific growth rate of unfed yolk-sac larvae were strongly influenced by the female. Equivalent amounts of variation in larval resistance to starvation were explained by maternity and bi-parental interaction. Paternity alone did not explain a significant amount of variation for the traits or processes examined. The bi-parental interactions reported demonstrate a female's choice of mate could significantly influence the early life survivorship of Baltic cod offspring.

Sperm competition experiments were conducted to test the null hypothesis that sperm quality is not affected by male body size in Atlantic cod (Gadus morhua). Genetic markers (allozymes) were used to determine the proportion of larvae sired by pairs of males when their sperm was combined with eggs of a single female simultaneously. Significant differences in fertilization success between males were not explained by differences in body size. Fertilization success was positively associated with male condition factor (K) and with spermatozoa density in each male's semen when equal volumes of semen from each male were used. Male K was positively associated with male fertilization success when the volume of semen used from each male was adjusted to add approximately equal numbers of spermatozoa from each male. The relative fertilization success of males varied depending on which female was the egg donor, suggesting that female \"choice\" at the gamete level may be occurring in cod.

Body size is often positively associated with mating success in fish. However, mating success may not accurately represent reproductive success (number of progeny produced). We tested the null hypothesis that reproductive success in male Atlantic cod, Gadus morhua, is not directly proportional to body size. Two allozyme loci and one minisatellite locus were used to estimate the proportion of larvae sired by pairs of males differing in body size and spawning with one female in each of eight tanks during an entire spawning season. Genotypes of progeny from 51 spawning events (egg batches) showed that both males fertilised eggs in each tank. Multiple paternity of larvae occurred in 35 batches. The estimated proportion of larvae sired by each male varied randomly among egg batches within tanks. Male size, condition factor, and total or relative body-weight loss over the season were not correlated with the estimated proportion of larvae sired by each male during the spawning season. Relative activity of males wasmarginally associated with male reproductive success, with more active males siring a larger proportion of larvae. Male reproductive success was affected by female size, with males much larger (25% total length) than females siring a smaller proportion of larvae.

A significantly greater proportion of Atlantic cod (Gadus morhua) sperm were motile in the presence of ovarian fluid and egg compared with seawater. Sperm mean and maximum swimming speeds were also significantly greater in the presence of ovarian fluid and egg compared with seawater. However, there was no significant difference in path linearity among treatments. We also examined the interaction between maternal stimuli (egg and ovarian fluid), time sperm spent in seawater prior to exposure to each stimulus, and salinity on proportion of motile sperm and their swimming behaviours. Proportion of motile sperm decreased significantly with a decrease in salinity in the presence of both maternal stimuli. Proportion of motile sperm also decreased with time spent in seawater prior to exposure to ovarian fluid but not to an egg. Both mean and maximum swimming speeds were maintained in the salinity range of 20-30 ppt and only declined significantly at lower salinities (15 and 17.5 ppt). Mean and maximum swimming speeds decreased with time spent in seawater. This study demonstrates the importance of maternal factors when examining sperm swimming behaviour and highlights the significance of maternal-paternal gametic interactions in understanding fertilization success.