Characterization of scale abnormalities in pinfish, Lagodon rhomboides, from Biscayne Bay, Florida

Correlations between marine habitat degradation and the prevalence of abnor malities and diseases in populations can provide a starting point for under standing the effects of changes in environmental conditions on marine organ isms. The present study characterized the features of scale disorientation (SD), a common morphological anomaly encountered in pinfish, Lagodon rhombo ides, in Biscayne Bay, Florida (U.S.A.). Scale disorientation consisted of discrete patches of scales rotated dorsally or ventrally away from the norm al scale position without any projection of the scales outwards from the bo dy surface. The direction of scale growth within the patches varied from no rmal to a minor misalignment to a complete reversal of direction. The sever ity of SD, defined as the percentage of body surface area affected, varied from 1 to 34% with a mean of 9.3%. Affected fish monitored in the laborator y demonstrated a proportional growth of SD areas such that the percentage o f body surface affected did not change as the fish grew. Scale disorientati on was more prevalent in the northern region of the bay, an area known to b e more contaminated. Scales from SD areas exhibited significantly abnormal morphology with larger average focus diameter, smaller size, more elongate shape and fewer radii relative to normal scales. Experimental removal of sc ales demonstrated that normal scales regrew in normal orientation and morph ology while those from SD areas regrew in abnormal orientations and morphol ogies. Experiments in which fish were exposed to acute and chronic injuries indicated that these physical traumas were insufficient to directly induce formation of scale disorientations typical of those seen in the wild. Obse rvations of pinfish in the laboratory revealed that SD areas can appear spo ntaneously in normal juvenile and adult fish. These new SD areas developed relatively rapidly, did not require prior scale loss and remained stable in size after first appearance. Although the etiology of SD remains unknown, the significant difference in prevalence of this syndrome between regions o f Biscayne Bay having different levels of sediment contaminants suggests th at environmental factors may be important in development of SD.