Sublethal effects of diazinon on the structure of the testis of bluegill,Lepomis macrochirus: a microscopic analysis

A histopathological analysis of the testis exposed to diazinon, an organophosphorus pesticide was conducted. The testis from the control fish exhibited a normal histological structure with a round, oval or somewhat rectangular shaped with closely associated seminiferous tubules. The seminiferous tubules were surrounded by a layer of connective tissue with myoid cells, Leydig cells, blood vessels, lymph vessels and nerves. Upon exposure for 24 h, the overall structure of the testis looked disrupted and more often the sperm cells appeared to be somewhat larger, but spermatid were smaller than that of the control group. The 48 h exposure caused more dense and closely associated seminiferous tubules. The 72 h exposure induced dilation of the seminiferous tubules and their lumen. Ninety-six hours exposure induced more loose and disrupted structures. In this group (96 h), there was a significant reduction in both lumen and seminiferous tubule size in comparison with the control, 24, 48, and 72 h groups. After 2 weeks of exposure hardly any lumen was seen, which imparted more dense and compacted structures. The biometric analysis gave a highly significant increase in the diameter of the seminiferous lumen. After 48 h of exposure a significant reduction was seen in diameter in comparison with that of the control group. Seventy-two hour exposure indicated an increase in diameter, whereas 96 h exhibited another decrease. One week caused the diameter to increase whereas 2 weeks of exposure caused them to decrease again. The increase in diameter of the seminiferous tabule may be caused by weakening of the surrounding connective tissue and myoid cells, due to exposure to diazinon. The change in the diameters of the seminiferous tabules was very irregular. No apparent co-relation was found between the size of the fish, body weight and weight of the testis after they have been subjected to different exposure periods. There was significant change in the germ cells' diameters. As the germ cells are the essential first step in the process of spermatogenesis, their size reduction may hinder the production of viable spermatozoa, endangering the population dynamics. In order to find out the pathways of this pesticide effects, we propose to study the histopathology of pituitary gland a vital organ of the reproductive axis.