Yvan Lambert

Food intake and growth of adult Atlantic cod (Gadus morhua L.) reared under different conditions of stocking density, feeding frequency and size-grading

The combined effects of stocking density, feeding frequency and size-grading on feeding and growth of adult Atlantic cod (Gadus morhua L.) were measured in a series of four experiments. Specific growth rates decreased from a maximum of 1.08%/day at 2 kg/m3 stocking density to 0.66% at 40 kg/m3 density. Over 2 months, biomass increased 60–89% in fish stocked at low densities (<10 kg/m3) but only by 50% in those held at high stocking density (40 kg/m3). Cod fed to satiation twice a week had lower growth rates than those fed three or five times a week, but growth rates did not differ significantly between cod fed three and five times weekly. However, when stocked at 40 kg/m3, cod fed five times a week tended to show better growth than cod fed three times per week. Growth rates of larger maturing cod with high initial condition factors did not improve when feeding frequency was increased to more than two meals per week. Size-grading had a significant effect on growth. Growth rates of 0.50% and 0.45%/day were recorded for cod that were size-sorted and stocked at 10 and 30 kg/m3, respectively, compared to 0.78% and 0.55%/day for cod of the same sizes reared in unsorted groups at the same densities. Size-sorting had no significant effect on growth rates of cod stocked at 40 kg/m3.

Winter and spring changes in condition factor and energy reserves of wild cod compared with changes observed during food-deprivation in the laboratory

Atlantic cod were food-deprived for a period of 84 days at three temperatures (2, 6, 10 � C), and changes in the liver, gonads and somatic weights, and muscle and liver water contents were monitored and compared with changes observed in wild cod over winter in the northern Gulf of St. Lawrence. Total lack of food during the period January–April would have caused condition to decline to a level at which very high mortality takes place. Actual changes in condition in wild cod were less than predicted from the laboratory experiments except during the period April–May at the onset of spawning. Thus, wild cod were able to meet part of the metabolic costs during winter through occasional feeding, as confirmed by stomach content data. We conclude that previous estimates of natural mortality associated with poor condition in spring were not biased by the selective mortality of poor-condition fish in winter. Crown Copyright 2003 Published by Elsevier Ltd on behalf of International Council for the Exploration

Alternative methods for measuring energy content in winter flounder

Abstract Indices of energy reserves may represent interesting parameters that can be used as bioindicators in environmental studies. The goal of this study was to identify a water–energy model that could predict energy reserves in winter flounder Pseudopleuronectes americanus. Winter flounder kept in captivity and fed different food types (either capelin Mallotus villosus or Atlantic herring Clupea harengus, amphipods Anonyx sarsi, and wet pellets) for 2, 5, and 14 months and wild fish captured in May, July, and October were used to show a large range in energy content. High levels of correlation were observed between water and energy contents in fish carcasses (r 2 = 0.82) and muscle (r 2 = 0.75). However, the biochemical composition of the liver remained relatively constant, despite changes in the hepatosomatic index. The condition factor (somatic weight/length3) was associated with energy reserves (i.e., water contents), but the coefficients of determination were smaller (0.18 < r 2 < 0.34). We found t...

The Effects of Two Rearing Salinities on Survival and Stress of Winter Flounder Broodstock.

The goal of this study was to determine rearing conditions that would improve the survival of broodstock of winter flounder Pleuronectes americanus. We hypothesized that keeping wild winter flounder in iso-osmotic water would reduce the energy costs related to osmoregulation; the resulting energy gain could then be used for growth or immune responses. Eighty fish were randomly separated into four tanks, two containing seawater (SW; 28.7 ± 0.9‰ (mean ± SD)) and two containing brackish water (BW; 14.7 ± 1.7‰). Fish were sampled after 2 and 5 months of captivity for evaluation of their condition and stress status. Between the second and fifth months, the condition index increased significantly in both salinity groups, whereas body water content decreased. No salinity effect in terms of growth, condition, or energy reserves was found. However, the fish in BW showed much lower mortality. We found that the fish in SW had higher levels of the physiological indicators of stress than those in BW, which could have increased the risk of opportunistic infections in the former. Also, thrombocytes were absent in the SW fish after 2 months of captivity, which may have contributed to some mortalities. The lower resistance of certain opportunistic pathogens to BW is another possible explanation as to why fish in BW had lower occurrences of infectious diseases.

The Effects of Latitudinal Origin and Paternal Contribution on Larval Growth of Winter Flounder in a Northern Environment

Abstract Three stocks of winter flounder Pseudopleuronectes americanus are currently defined in the northwest Atlantic region: One south of Cape Cod, Massachusetts, one north of it, and a third on Georges Bank. Our objectives were to determine whether the different populations along this latitudinal gradient have similar larval development characteristics in a coldwater environment and to test the paternal contribution to larval development. We crossed breeders that had been captured on their natural spawning sites in Passamaquoddy Bay, New Brunswick, and Baie des Chaleurs and the St. Lawrence estuary, Quebec, to produce pure-strain families (year 1) and hybrids (year 2). Larvae were reared under the salinity and temperature conditions of the St. Lawrence estuary, the northernmost site in our study. Total length and maximum width were measured from hatching to settlement. In the wild population from the St. Lawrence estuary, males were shorter and in better condition and females produced smaller eggs than...

Evaluating the use of the autodiametric method for estimating fecundity of Reinhardtius hippoglossoides, a species with an unusual oocyte development strategy

Evaluating the use of the autodiametric method for estimating fecundity of Reinhardtius hippoglossoides, a species with an unusual oocyte development strategy R. Dominguez-Petit*, R. M. Rideout, D. Garabana, Y. Lambert, M. Hermida, and M. J. Morgan Spanish Institute of Oceanography, Oceanographic Centre of Vigo, Vigo, Spain Institute of Marine Research-CSIC, Vigo, Spain Fisheries and Oceans Canada, Northwest Atlantic Fisheries Centre, St John’s, NL, Canada Spanish Institute of Oceanography, Oceanographic Centre of A Coru~na, A Coru~na, Spain Fisheries and Oceans Canada, Institute Maurice-Lamontagne, Mont-Joli, QC, Canada *Corresponding author: tel: þ34 98 646 2271; fax: 986498626; e-mail: rosario.dominguez@ieo.es.