Selected biomarkers of health were examined in 50 post-spawning cod Gadus morhua collected in November 2015 from the southern Baltic. The biomarkers included condition factor (CF), macroscopic lesions, histopathology of spleen, liver and gonads, and morphometry of follicular atresia and hepatic and splenic melanomacrophage cells (MMC). All fish appeared in good body condition. One fish had a dermal ulcer, and in seven, macroscopic nematodes were noted within body cavity. Microscopic lesions in the liver included biliary myxozoanosis, microsporidial and necrocentric granulomas, parasitic hepatitis, multifocal necrosis, foci of cellular alterations, spongiosis, peliosis and cytoplasmic fibrillar inclusions. The spleen and gonads had microsporidial and/or necrocentric granulomas. Some of the biomarkers showed differences as compared to spawning cod collected in May from the same location in 2012, most importantly values an order of magnitude lower for splenic MMC in post-spawning fish. In post-spawning fish, there were statistically significant correlations between MMC, CF, follicular atresia, parasitic hepatitis and microsporidiosis. This is the first comparison of biomarkers of health in post-spawning and spawning Baltic cod. Future studies need to examine the relationships of biomarkers to levels of pollutants in the environment and in tissues of cod.
The International Council for the Exploration of the Sea (ICES) listed the cod Gadus morhua as one of the target species for environmental biomonitoring in the Baltic, but only limited data on morphological biomarkers in this fish have been published so far. This pilot study examined cod tissues for the presence of selected biomarkers that have been studied in other target fish species for this region: flounder Platichthys flesus, herring Clupea harengus, and eelpout Zoarces viviparus. Twenty cod were collected in May 2012 off the Polish coast near Ustka. The biomarkers studied included condition factor, macroscopic lesions, morphometry of hepatic and splenic melanomacrophages, ovarian follicular atresia, and histopathology of spleen, liver, and gonads. All fish appeared in good body condition and had no macroscopic lesions except for one with multifocal dermal ulcers. Microscopic lesions were present in all fish, and included biliary myxozoanosis, ovarian microsporidiosis, larval nematodes compatible with Anisakidae, one case of intravascular trematodiasis, necrocentric granulomas, mild inflammatory and toxicopathic hepatocellular lesions, and marked accumulations of splenic melanomacrophages. This pilot study expands the types of microscopic lesions that have been documented as part of biomonitoring efforts in Baltic cod.
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