engleski

Histological examination of mullets (Mugil sp.) as a possible tool in assessing environmental impact of aquaculture

Fish farming has an impact on the environment due to organic and inorganic nutrients loss, discharge of applied veterinary products etc. Among them, the impact caused by the release of waste products of fish metabolism as well as unused food is the most important. One of the most important constraints to the further development of the Mediterranean aquaculture are environmental concerns, related to the location of the farms and the impact of the efluents on the surrounding environment. Mullet (Mugil spp.) is a cosmopolitan species commonly found in coastal regions and more importantly around the cages of farmed fish. Furthermore this species is known to eat waste food and detritus around and bellow sea cages. Therefore two groups of Mullet were sampled, one around cages of farmed Sea bass and the other from wild population. Basic diagnostic procedures were carried out and liver, spleen and rear kidney were sampled for histological examination. The aim of this study was to determine whether fish farming has an impact on fish living near the cages. 104 fish were sampled in the vicinity of floating cages on Sea bass farms along the East Adriatic coast. The control group were 55 wild fish, sampled during the harvesting of the Tarska bay. Samples from the liver, spleen and rear kidney were processed for the histological examination. Paraffin sections 5&#181; m thick were stained with hematoxylin and eosin and analysed by light microscope (Olympus BH-2) at 40 X to 1000 X magnification. Results of histological examination revealed that MMC (melanomacrophage centers) were more numerous in all examined organs, however only in spleen significantly (t=2.69, p<0.05). Fat infiltration/degeneration of liver was not found in fish from wild population, while one third of fish sampled on fish farms had increased fat content. Ocurrence of vacuolar/ hyaline degeneration was significantly more common in mullets sampled in the vicinity of farmed fish (&#967; 2=5.11, p<0.05) as well as the mean number of atrophied glomeruli was significantly higher (t=3.15, p<0.05). Only accumulation of inflammatory cells was more frequent in fish from wild population, though insignificantly (&#967; 2=5.21, p>0.05). The results of the present study indicate that the intensive culture of European sea bass affects histology of mullets living around floating cages. Although these effects might be important locally, little is known of wider impact on wild population. Thus, possible interactions between wild and cultured population such as transmission of parasites and pathogens as well as potential of the development of eutrophic problems in the vicinity of cage farms require further studies .

histology; mullet; environment

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