Variability of microsatellite loci of Greenland cod Gadus ogac Richardson 1836: Comparison with other species of Gadus genus (Gadidae)
А. Н. СтрогановК. И. АфанасьевKnut Eirik JørstadMarie Storr‐PaulsenА. М. ОрловГ. А. РубцоваT. A. Rakitskaya
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Atlantic cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) are two commercially important marine fishes impacted by both overfishing and climate change. Increasing ocean temperatures are affecting the physiology of these species and causing changes in distribution, growth, and maturity. While the physiology of cod has been well investigated, that of haddock has received very little attention. Here, we measured the metabolic response to increasing temperatures, as well as the critical thermal maximum (CTmax), of cod acclimated to 8 and 12 °C and haddock acclimated to 12 °C. We also compared the swimming performance (critical swimming speed, Ucrit) of cod and haddock at 12 °C, as well as the Ucrit of 12 °C-acclimated cod acutely exposed to a higher-than-optimal temperature (16 °C). The CTmax for cod was 21.4 and 23.0 °C for 8- and 12 °C-acclimated fish, respectively, whereas that for the 12 °C-acclimated haddock was 23.9 °C. These values were all significantly different and show that haddock are more tolerant of high temperatures. The aerobic maximum metabolic rate (MMR) of swimming cod remained high at 16 °C, suggesting that maximum oxygen transport capacity was not limited at a temperature above optimal in this species. However, signs of impaired swimming (struggling) were becoming evident at 16 °C. Haddock were found to reach a higher Ucrit than cod at 12 °C (3.02 vs. 2.62 body lengths s-1, respectively), and at a lower MMR. Taken together, these results suggest that haddock perform better than cod in warmer conditions, and that haddock are the superior swimmer amongst the two species.
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Adult Atlantic cod (Gadus morhua) produce antifreeze glycopeptides during the winter which help to depress the freezing point of their blood plasma to approximately −1.2 °C. Since the temperature at which fish can freeze and die approximates the freezing point of their blood plasma, it is evident that adult cod do not have the capacity to survive in ice-laden waters when the water temperatures drop to −1.5 °C. Templeman and Fleming hypothesized that small cod are more adapted to cold water than adults. The present study documents the fact that the blood plasma freezing points of juvenile cod (mean length = 33 cm, 3-yr-olds) were significantly lower than those of adult cod (> 45 cm) (juvenile, −1.55 °C; adult, −1.23 °C). This difference was largely attributable to the doubling of plasma antifreeze glycopeptide levels in the juvenile cod. These results directly support Templeman and Fleming's hypothesis and indicate that juvenile cod, unlike adults, are capable of surviving the icy marine conditions which prevail along the northeast coast of Newfoundland during the winter.
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We describe geographic and host size related trends in the prevalence of the gill parasite Lernaeocera branchialis (Copepoda, Pennellidae) infecting Atlantic cod (Gadus morhua) in coastal Newfoundland and Labrador and assess the effect of parasitism on cod survival in the wild. Using cod-tagging studies conducted between 1962 and 1989, we test three null hypotheses: (1) parasite prevalence in the Northwest Atlantic is latitudinally invariant, (2) infected cod have the same survival probability as parasite-free cod, and (3) parasite prevalence is independent of fish length. The first hypothesis is rejected given a significantly negative relationship between prevalence and latitude. The second hypothesis is rejected in one geographic region where 8% fewer infected cod from northeast Newfoundland were recaptured relative to uninfected cod. This implies that parasitized cod can suffer an 8% differentially higher mortality relative to nonparasitized cod. The third hypothesis is rejected because the proportion of cod infected was generally greatest in the 43-49 cm length-class and decreased significantly with increasing length. Differential survival between infected and uninfected cod within length-classes was not observed. The use of L. branchialis as a population marker warrants caution. The parasite has the potential to affect the recovery of depleted Northwest Atlantic cod stocks in a geographically differential manner.
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The immunoglobulin (Ig) level in serum from Atlantic cod, Gudus morhua L. (Teleostomi, Gadiformes), was measured using ELISA. Cod serum contains 5.62 ± 0.19 mg Ig ml, which constitute 17.2% of the total serum proteins. Polyclonal and monoclonal antibodies (Ab) against cod‐Ig were used for cross‐reactivity studies in sera from other species. The cross‐reaction with polyclonal Ab was high in gadifom fish, and low or absent in the other tested species. Immunoprecipitation showed that the Ab only binds to the Ig of the serum from the other species. The results within the gadiform group indicate that (1) Gadidae and Lotidae are more closely related to each other than to Merluccidae, (2) Phycidae is more distant related to Lotidae than earlier considered, (3) Zoarcidae seem to be more distant related to Gadus than other species of Gadiformes. These results support recent revisions of the systematics of Gadiformes. Monoclonal Ab against the heavy chain of cod‐Ig show no, or small (< 15%) cross‐reactions with serum from gadiform species. One monoclonal Ab against the light chain shows high cross‐reaction and also binds to Ig from species outside the Gadiformes, indicating that the light chain of Ig might be more conserved than the heavy chain.
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It is important to have good estimates of tag reporting rates when inferring exploitation rates and other mortality rates from tagging experiments. We estimate the reporting rates of single- and double-tagged Atlantic cod (Gadus morhua) caught in commercial fisheries around coastal Newfoundland, Canada, based on an extensive series of multi-reward tagging experiments conducted during 1997–2004. Reporting rates for single-tagged cod varied from 58% to almost 100%, with significant temporal and spatial variability. The odds of reporting a double-tagged cod was almost double that of a single-tagged cod. Returns from double-tagged cod allow us to estimate tag shedding rates. Tag shedding rates suggested that 22% of fish lost their tag during their first year at liberty; subsequently, tag shedding rates were much lower (<10%). We also found that twice as many fish lost tags when the tags were attached anteriorly at the base of the first dorsal fin compared with a position more towards the posterior end.
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