Size, condition, and age of female-Icelandic cod Gadus morhua were correlated to the size of their eggs and newly hatched larvae. A positive relationship was detected between egg size and some larval viability parameters, including the age at first feeding, successful development of a swimbladder, and specific growth rates during the first 15 days after hatching. These results reveal that the viability of cod larvae is related to attributes of the spawning females and that this information is important to our understanding of stock-recruitment relationships.1998 The Fisheries Society of the British Isles

Results from laboratory experiments showed that food-unlimited growth rate (G) of Atlantic cod (Gadus morhua) declined linearly with fish weight (W) on a log–log scale at six different temperatures: 2, 4, 7, 10, 13, and 16°C. The intercept (αi) and slope (βi) of these regressions increased linearly with temperature (T), implying that G = αi W βi, where αi = γ1 + δ1T and βi = γ2 + δ2T. Nonlinear fit of the four-parameter model showed that γ1 was not significantly different from 0, and thus the following three-parameter model is suggested for the food-unlimited growth rate of cod ranging in size from 2 to 5000 g at any temperature from 2 to 16°C: G = (0.5735T)W(–0.1934–0.02001T). The results indicate that temperature in this size range has a much greater effect on the growth rate of small juvenile cod than on that of larger cod. The model predicts that the optimal temperature for growth of cod decreases with increased size of fish, from 14.3°C for 50-g fish to 5.9°C for 5000-g fish. Growth curves were derived for cod at constant and seasonally variable temperatures. Weight-at-age was calculated for different temperatures.

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Aims:  To assess the effects of bacterial treatment at the earliest stages of cod rearing on the microbial load, larval development and performance, testing three bacterial strains (Carnobacterium divergens V41, Arthrobacter sp. and Enterococcus sp.) in vivo that were previously shown to have inhibitory potential towards fish pathogens in vitro. Methods and Results:  A bacterial mixture was added eight times to the rearing water from the prehatch to the mid‐larval stage (a 38‐day period). Microbiological analysis of ova, larvae and rearing water was performed regularly. Larval performance and development were evaluated by survival rate, hypersalinity tolerance and physiological measurements. Different larval survival rates were observed within and between treatments, and possibly explained by variations in larval microflora and established probionts. Larvae from one silo, which had been bathed in the bacterial suspension, showed the highest survival rate (42·1%), lowest Vibrio levels, and were significantly heavier (19·3%) and more stress tolerant than control larvae (P < 0·01). This coincided with the intestinal establishment of two of the tested bacteria. Conclusions:  Arthrobacter and Enterococcus strains added regularly to the rearing water from the postfertilized egg stage can become established in larval gastrointestinal tract. The Enterococcus strain was associated with increased larval growth, performance and microflora control, indicating its probiotic nature. Significance and Impact of the Study:  Regular application of autochthonous probionts may promote larval welfare, development and stress tolerance at early stages, hence increasing production yield in intensive cod larviculture.

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