Diploid Rainbow Trout Oncorhynchus Mykiss Research Articles

Comparison of reproductive development in triploid and diploid female rainbow trout Oncorhynchus mykiss

The diploid rainbow trout Oncorhynchus mykiss reached sexual maturity 3 years after hatching and its oogenesis underwent four stages, which were oogonia, primary oocyte, secondary oocyte and egg. Reproductive development and hormone changes of 4 to 35 month-old female O. mykiss were investigated using histological and radioimmunoassay methods in order to provide a theoretical and practical basis for the use of triploid female O. mykiss. The oogonium of the triploid female could develop into the oocytes of the prophase with abortion occurring later; the oogonium was surrounded by stroma cells to form the oogonium cluster and the gonads showed a virilescent tendency when the oogonium clusters were gradually replaced by spermatogenic-like cytocysts. After 13 months, amounts of gonadotropic hormone (GtH-I, GtH-II) and oestradiol (17beta-E(2)) in triploid females were lower than in diploid fish at corresponding time periods, but the amounts of testosterone (T) increased consistently after 21 months and were more than in diploid fish in the corresponding time periods (P > 0.05). The infertility of triploid females resulted from meiosis failure, which caused developmental abortion of oocytes and oogonium formed cytocysts before the prophase oocytes. The cytocyst formation was due to the lack of the normal interaction of ovum and follicular cells, the development of follicular cells producing steroids were inhibited, the arylate path from T to 17beta-E(2) was interrupted, concentration of 17beta-E(2) decreased and concentration of T increased in the blood, the content of vitellogenin (Vg) decreased in the liver with a low 17beta-E(2) and high T caused to ovaries to show a tendency to be virilescent.

Coronary vascular volume remodelling in rainbow troutOncorhynchus mykiss

The 34% increase in relative ventricular mass (Mrv) resulting from chronic anaemia (induced by an intraperitoneal injection of phenylhydrazine hydrochloride) was accompanied by a 117% increase in coronary vascular volume of diploid rainbow trout Oncorhynchus mykiss. Coronary vascular volume of normocythemic triploid fish was similar to that of normocythemic diploid fish despite a larger Mrv. These observations, in combination with previous studies, suggest that the vascularity of compact myocardium in O. mykiss can vary independently of Mrv.

In vitro cardiac performance in triploid brown trout at two acclimation temperatures

The maximum values for heart rate (fH), stroke volume (VH), cardiac output (Q) and myocardial power output, measured in vitro with a perfused heart preparation, as well as the isometric force‐frequency relationship for atrial and ventricular muscle strips, in triploid brown trout Salmo trutta were all comparable with established information for diploid rainbow trout Oncorhynchus mykiss. Therefore, it was concluded that triploidy is not associated with a major deficiency in maximum cardiac performance. However, a heightened sensitivity to ryanodine was discovered, which indicated an enhanced role for the sarcoplasmic reticulum in excitation‐contraction coupling in these triploid fish. It is suspected that the enhanced role of the ryanodine receptor may be a cellular compensation related to larger cardiac myocytes. It was also clearly established that there was a plateau in maximum cardiac performance between 14 and 18° C and this plateau might be a contributing factor to the reduced factorial aerobic scope and increased fish mortality observed at 18° C.

Susceptibility and humoral response of brown trout X lake trout hybrids to infectious hematopoietic necrosis virus: a model for examining disease resistance mechanisms

A model system for examining resistance mechanisms of interspecific hybrids to a viral disease was designed and tested. Diploid rainbow trout Oncorhynchus mykiss and heat-induced triploid brown trout Salmo trutta female X lake trout Salvelinus namaycush male hybrids (or brake trout) were evaluated for susceptibility and humoral response to infectious hematopoietic necrosis virus (IHNV). The triploid hybrids exposed to waterborne virus had a cumulative mortality of 2% ( 1 49 ) compared to 53% ( 27 51 ) in the pure species diploid rainbow trout. Virus neutralization activity was not detected in serum obtained from control fish, however, all serum pools from surviving rainbow trout exposed to waterborne IHNV had antibody titers significantly higher ( P < 0.05) than pooled sera from brake trout. This suggested that the IHNV resistance of the hybrids occurred at the cellular level that minimized infection and internalization of the virus. To determine if resistance was a function of external epithelial cell attachment and entry, susceptibility was also evaluated to intraperitoneally injected virus. Mortality was also significantly less ( P < 0.001) in hybrid trout (mean weight, 10.2 and 26.2 g) injected with IHNV compared to rainbow trout (mean weight, 22.3 and 90.0 g). The decrease in mortality was associated with a strong humoral response where 70% of the surviving triploid hybrids had antibody titers ≥ 640. Necrosis of the renal and splenic interstitial hematopoietic tissue of rainbow trout was typical of lesions due to IHNV infection, however, the lesions in the hybrids were less extensive and severe. The decreased severity and extent of the lesions correlated with the decreased mortality and high antibody titers demonstrated in the hybrid trout as compared to the matched group of rainbow trout. These results suggest that more than one host factor can affect resistance to IHNV.

Characteristics of Muskellunge Spermatozoa I: Ultrastructure of Spermatozoa and Biochemical Composition of Semen

We investigated the ultrastructure of spermatozoa and some physiological and biochemical parameters of semen in muskellunge Esox masquinongy. Ultrastructure of spermatozoa analyzed with scanning and transmission electron microscopes revealed a spherical head, 1.5 um in diameter. Unlike the spermatozoa of other teleost fishes, an elongated midpiece with abundant mitochondria was found to be characteristic for muskellunge spermatozoa. Three techniques for measuring sperm concentration, counting with a hemacytometer, spermatocrit, and spectrophotometric methods, provided similar results (19.7 ± 6.1 × 109 sperm/mL). The spectrophotometric method is recommended because it is rapid and requires only small amounts of semen. Ionic concentrations and osmolality (289 ± 16.8 milliosmols/kg) of seminal plasma were reported. Sodium (129 ± 6.7 mM) and potassium (27.88 ± 3.27 mM) concentrations were closer to levels found in the seminal plasma of salmonids than cyprinids. Aspartate aminotransferase (AspAT) activity was measured with and without supplement of pyridoxal phosphate (PLP) from sperm extracts. A 96% increase of AspAT was found when PLP was included in the assay. We confirmed the presence of antiproteinase activity (against cod trypsin) in seminal plasma of muskellunge. Using the flow cytometry method, we estimated that the DNA stainability of muskellunge spermatozoa was 0.188 ± 0.008 times that of red blood cells (TRBC) from diploid rainbow trout Oncorhynchus mykiss. The DNA stainability of muskellunge spermatozoa was significantly lower than that of muskellunge embryonic cells, which was 0.474 times that of the TRBC (2.21 pg DNA/cell, based on the internal standard of TRBC of 4.66 pg DNA/cell).