Seasonal changes in serum gonadotropin, testosterone, 11-ketotestosterone, and estradiol-17 beta levels and their relation to tumor burden in gonadal tumor-bearing carp x goldfish hybrids in the Great Lakes.

The hybrids of carp (Cyprinus carpio) and goldfish (Carassius auratus) collected from the lower Great Lakes between 1978 and 1981 exhibited a high frequency of gonadal neoplasms and apparent sterility, conditions which were rare in the parental species. A pronounced hyperplasia of gonadotropic cells in hybrids resulted in the accumulation of large stores of biologically active gonadotropin (GtH) in the pituitary gland. Serum GtH levels were generally higher in hybrids than in carp collected from the same areas, but seasonal trends were similar for both species. Among hybrids, tumored individuals had higher serum GtH levels than nontumored individuals. Serum levels and seasonal trends for testosterone (T), 11- and ketotestosterone (11-KT), and estradiol-17 beta (E2) were, for the most part, similar when carp and nontumored hybrids of the same gender were compared. Serum levels of T and 11-KT (but not E2) were generally higher in tumored hybrids when compared to nontumored individuals. High serum steroid levels were related to a specific tumor type, possibly of Sertoli cell origin. Although the etiology of the gonadal tumors is not yet known, the serum levels of gonadal steroids in hybrids make it unlikely that a lack of steroidal feedback is responsible for the gonadotrop hyperplasia.

Gonadotropin content of the pituitary gland of gonadal tumor-bearing common carp x goldfish hybrids from the Great Lakes, as assessed by bioassay and radioimmunoassay.

The hybrids of carp (Cyprinus carpio) and goldfish (Carassius auratus) collected from the lower Great Lakes between 1978 and 1981 exhibited epizootics of gonadal neoplasm which were rare in the parental species. The pituitary glands of hybrids were, on average, 2.5 times larger than that of carp of similar body size. Histologically, the hypertrophy was due to hyperplasia of proximal pars distalis basophils (the presumptive gonadotropes). Using a carp gonadotropin (GtH) radioimmunoassay it was found that hybrid pituitaries contained more GtH than sympatric carp and that pituitary GtH concentration in hybrids was positively correlated with pituitary weight. Both this and histological evidence suggested that gonadotrope hyperplasia was a progressive event. Two heterologous gonad bioassays indicated that hybrid GtH had biological activity. Whether pituitary hyperplasia in hybrids is a primary problem or secondary to gonadal sterility has not been determined.

Plasma kinetics of injected recombinant chicken somatotropin in juvenile coho salmon (Oncorhynchus kisutch) using a homologous radioimmunoassay.

Although somatotropins are potent growth promoters in salmonids, there is little information on how these proteins are metabolized by poikilotherms. In the present study, the plasma uptake and clearance rates of recombinant chicken somatotropin (rcGH) were investigated in juvenile coho salmon (Oncorhynchus kisutch). Two doses of rcGH were administered by intraperitoneal (ip) or intramuscular (im) injection and blood samples were collected over a period of 32 days. A specific radioimmunoassay was validated and used to discriminate rcGH from endogenous somatotropin. Plasma rcGH concentration was proportional to the dose delivered, but uptake and clearance rates were found to be independent of dose (between 0.5 and 5.0 µg/g). Absorption of rcGH into the plasma was faster from the im site, but the peak levels attained were similar after im or ip treatment (using the same dose) as was area under the curve. Plasma half-life was calculated from the declining phase of the uptake/clearance profile but the results were biased by the concurrent uptake of rcGH from the ip or im reservoir of material, resulting in an over-estimation of the true half-life value. Effective treatment doses and intervals are discussed.

An epizootic of diffuse glomerulonephritis in white perch (Roccus americanus) from a heavily polluted industrial basin in Lake Ontario.

Examination of 43 white perch from a heavily polluted water basin showed all had severe diffuse glomerulonephritis. There were fibrinoid necrosis of tuft vessels, especially the afferent and efferent arterioles, and thickened basement membranes which ultrastructurally contained dense deposits in a subendothelial location. None of these lesions was found in white bass, a closely related species, from the same source nor in white perch from other relatively nonpolluted sites in Lake Ontario or Lake Erie. This is a dramatic example of a rare lesion in fish and possible represents an immune-complex mediated response to an environmental pollutant.

Isozyme expression in F1 hybrids between carp and goldfish.

Interspecific genetic differences in malate dehydrogenase (MDH), lactate dehydrogenase (LDH), superoxide dismutase (SOD), and esterase (EST) isozymes in carp (Cyprinus carpio) and goldfish (Carassius auratus) were used to examine the allelic expressions in the hybrid between these species. A unique liver SOD and muscle LDH phenotype unambiguously identifies all presumed hybrid individuals. There was no evidence of F2 or backcross phenotypes in hybrid individuals. Liver MDH and EST phenotypes in hybrids show a preferential expression of goldfish isozymes. Variation in the levels of carp liver MDH isozymes may result from the polymorphism of a regulatory mutation effecting isozyme expression, leading to gene silencing after duplication.