Captive Atlantic cod (Gadus morhua) were fed at four ration levels (starvation, maintenance, moderate, and excess) for periods of 6–9 mo prior to and during spawning. At the end of the experiment, water, protein, glycogen, and fat contents of the liver, white muscle, and ovary were estimated. The depletion of the white muscle and liver was related to oocyte maturation and in particular to the proportion of eggs spawned (PES). The influx of protein into the ovary, the mean hydrated egg diameter, and the egg dry weight all reached maximum values at 10% PES and subsequently declined. Mean vitellogenic oocyte diameter was small prior to spawning but rose to a maximum at PES = 10%. Cod with high condition factors produced more previtellogenic oocytes and used a larger fraction during vitellogenesis. Actual fecundity of specimens deprived of food during the spawning period was between 20 and 80% of the potential fecundity depending on the nutritional status of the fish. Intensity of atresia in moderate ration fish increased from 0% at PES = 0% to 33% at PES = 80%. Estimates of durations of α-atretic vitellogenic oocytes varied between 10 and 13 d at 8 °C assuming a spawning period of 50 d.

Variability in the annual egg production of hatchery-reared Atlantic cod (Gadus morhua) was determined under stable experimental conditions. Egg size increased with fish age as an approximate step function. Comparing first-and second-time spawners, the variance in egg dry weight was 32% within individuals (i.e., the seasonal effect, the cod being a multiple-batch spawner), 55% between years, and 12% between individuals. In several repeat spawners, the curvature of the seasonal egg size curves showed little difference between years. The seasonal decrease in egg size was typically smaller in recruit spawners than in repeat spawners. There was no empirical evidence to suggest that environmental temperature regulates seasonal variations in egg size. The extent of egg swelling (i.e., the egg dry weight/diameter ratio) indicated a strong genetic component. Investment in ovarian growth was influenced by previous allocations as exemplified by annual, sinusoidal fecundity oscillations. Larger fish showed significantly longer spawning periods. The combined influence of maternal factors and the annual temperature variations noticed in the field during early stages suggests that larger larvae at the onset of feeding are more likely to survive.Résumé : On a déterminé la variabilité de la production annuelle d'oeufs chez des morues de l'Atlantique (Gadus morhua) et élevage dans des conditions expérimentales stables. La taille des oeufs augmentait avec l'âge des poissons en suivant approximativement une fonction en escalier. On a comparé le poids sec des oeufs chez des géniteurs à la première et à la deuxième ponte, ce qui a donné une variance de 32% chez les individus (ce qui correspond à l'effet saisonnier, la morue ayant plusieurs pontes pendant la saison), de 55% entre les années et de 12% entre les individus. Chez plusieurs géniteurs ayant frayé plusieurs fois, la forme des courbes saisonnières de la taille des oeufs n'indiquait que peu de différences d'une année à l'autre. La diminution saisonnière de la taille de ceux-ci était typiquement plus faible chez les nouveaux géniteurs que chez les anciens. Rien ne permet de croire que la température du milieu régule les variations saisonnières de la taille des oeufs. L'importance du gonflement des oeufs (c.-à-d. le rapport poids sec/diamètre de l'oeuf) semblait indiquer l'existence d'un important facteur génétique. L'investissement dans la croissance des ovaires était influencé par des investissements antérieurs similaires, comme le montrent les oscillations annuelles sinusoïdales de la fécondité. Les poissons de plus grande taille présentaient des périodes de ponte significativement plus longues. L'influence combinée de facteurs maternels et des variations de la température annuelle notées sur le terrain au cours des premiers stades indique que les larves qui sont les plus grosses au début de la période d'alimentation ont les plus grandes chances de survie. [Traduit par la Rédaction]

Aspects of the reproduction of reared cod, Gadusmorhua L., with special emphasis on the females, were studied under laboratory conditions. The fecundity and condition factor were 2.5 and 1.5 times. respectively, that of wild cod. A total of 18 spawning females were kept in separate tanks/ chambers, each with one or two males. Seven of the 18 females were classified as stressed, based upon behaviour, irregular spawning intervals and low fertilization rates of the eggs. The reared cod were found to spawn 17-19 batches. The number of eggs liberated in each batch normally followed a smooth, dome-shaped curve with time. The fertilization rate was normally 100%. Egg size decreased from first to last batch and the egg dry weight decreased by about 2&30%. The reared cod showed the same egg diameter to dry weight relation as wild cod. Egg diameter of first batch and maternal fish length were significantly positively correlated. The mean spawning interval for the female and the mean water temperature during its spawning were negativelycorrelated. Therearedcodspawnedin both the night and theday forabout 5C60days.

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