Effects of chloramine-T regime on juvenile rainbow trout (Oncorhynchus mykiss)

In this thesis, an experiment was devised to address the effects of chloramine-T on the production performance of juvenile rainbow trout during an 11-week growth trial conducted under conditions which simulated those of intensive aquaculture. Chloramine-T significantly suppressed the growth of treated fish $(\delta =7.3\%).$ The suppressive effects of chloramine-T were most dramatic in the early phase of the growth trial, but persisted throughout its duration. Subsequent studies were designed to address whether growth disturbances in treated fish are related to activation of a stress response and/or changes to gill and skin microanatomy. From these studies we found that exposure of trout to chloramine-T treatment regime used on the growth trial did not cause a significant change in cortisol levels or hematocrit, plasma glucose, sodium and chloride, leading to the conclusion that chloramine-T treatment was non-stressful to the experimental animals in this study. Fish treated with chloramine-T had an upward shift in the ratio of sialic-acid containing mucous cells compared to neutral mucous cells. Chloramine-T caused alterations in the epidermis of treated fish by decreasing its thickness and increasing the number of electron-dense vesicles in epithelial pavement cells. Gill lamellae of treated fish had expanded interstitial spaces and increased numbers of chloride cells. However, treatment did not affect the morphology of the mucous covering of the gill or skin, nor did it change the number of mucous $\rm cells/mm\sp2,$ or the electron density of the mucosomes of the skin. These tissue changes are probably insufficient to be considered as significant mechanisms accounting for the effect of chloramine-T on growth rates, and further study is therefore warranted to derive the mechanism. (Abstract shortened by UMI.).