Quantification of traumatic injuries in fish caused by the cormorant.

Cormorants cause damage to fish in aquaculture not only by consuming large number of fish but also by wounding them. Quantification of the actual damage in fish induced by wounding is important for reliable estimations of the overall loss in aquaculture caused by cormorants. In this study, specimens of mirror and scaly carp (Cyprinus carpio L.) injured by attacks of great cormorant (Phalacrocorax carbo L.) were collected from the “Ecka” fish farm in Serbia. Surfaces of superficial and open subepithelial wounds (expressed as a percent of the total body surface), estimated by computer-assisted image analysis, had mean values 10.66 ± 1.86 and 0.85 ± 0.90, respectively. Histological evaluation of wounds was performed by two scoring systems: system proposed by Bernet et al. (J Fish Dis 22:25–34, 1999) and modified system described by Wahli et al. (Aquaculture 225:371–386, 2003). The most frequent histopathological changes were disturbed epidermal structure and surface cell morphology and increased number of club cells (on more than 75% of specimens); increased number of melanocytes and their distribution in different layers in dermis; and enlarged hypodermis (more than 80% of samples) and myolysis (50% of samples). Comparison of wounds’ surfaces (surface of superficial injures) and histopathological changes, estimated by two scoring systems, revealed significant positive correlation. Bernet’s scoring system showed higher correlation coefficients, when compared with the modified Wahli’s scoring system.