Vertebral abnormalities in white crappies, Pomoxis annularis Rafinesque, from Lake Decatur, Illinois, and an investigation of possible causes

Abstract

Crappie, Pomoxis annularis, from Lake Decatur, Illinois, were reported to have a high incidence of backbone deformities, an investigation was initiated to determine both the mechanism of vertebral injury and the causative agent. Three groups of fish were collected: normally shaped and abnormally shaped crappies from Lake Decatur and control fish from abnormally shaped crappies from Lake Decatur and control fish from nearby Lake Sangchris. Analysis of organic and inorganic residue levels in fish tissue revealed no significant levels of contaminants in any of the three groups. Evaluation of the mechanical properties, biochemical composition, and density characteristic of vertebral bone showed no significant difference between the three groups. A myxosporidean parasite, found in both normal and abnormally shaped crappies from Lake Decatur, may have been a contributing factor leading to the spinal deformities. We believe that a short‐term exposure to organophosphate insecticides, may have occurred causing muscular contractions and resulting in vertebral damage and abnormally shaped fish.