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Older Fish (older + fish)
Selected AbstractsEffects of Varying Dietary Protein Levels and Feeding Frequencies on Condition and Reproductive Performance of Channel Catfish to Produce Hybrid CatfishJOURNAL OF THE WORLD AQUACULTURE SOCIETY, Issue 5 2009Herbert E. Quintero The interspecific hybridization of channel catfish, Ictalurus punctatus, females with blue catfish, I. furcatus, males has been identified as a method to further improve production; however, lack of spawning success has affected its commercial application. To facilitate our understanding of the interaction of brood stock nutrition and reproductive performance, we evaluated the interaction of feed quality and feeding frequency. Channel catfish females were classified into two genetic groups, namely, high and low spawning. The treatments were offered during the spring season 70,90 d prior to the start of the spawning season. Induced reproduction was performed using luteinizing hormone releasing hormone analog. Condition of the fish as well as reproductive performance using spawning success, egg production, egg size, and fertilization at 48 h were determined. Changing protein level of the diet from 32 to 42% did not influence spawning, fecundity, or fertilization, but affected egg size and biochemical composition of the eggs. Increasing the feeding frequency from three to six times per week negatively affected spawning in one of the two genetics groups, did not affect egg production and egg fertilization, but had a significant effect on egg size. Older fish performed better than younger fish in terms of spawning success and egg production. [source] Estimating the timing of growth rings in Atlantic cod otoliths using stable oxygen isotopesJOURNAL OF FISH BIOLOGY, Issue 3 2006H. Høie A technique involving micro-scale sampling of otolith carbonate and analyses of stable oxygen isotope composition was used to relate the zone appearance of the otolith to the seasonal temperature cycle. Otolith opacity could then be related to the timing of zone formation. Otoliths from two groups of Atlantic cod Gadus morhua held under known temperature conditions over a period of 4 and 6 years were examined. The otolith translucency followed the same pattern as the estimated temperature (from otolith ,18O values) in the yearly increments three and four, meaning that the translucent zones were deposited at the seasonal highest temperature in late summer and early autumn. The relative light intensities of otolith yearly increments five and six of older fish (deposited in the same years), however, were not significantly correlated to the estimated temperatures since increased otolith translucency also occurred at low temperatures. This might have been caused by stress in connection with gonad development or starvation during the spawning period. The results showed that this method of coupling otolith opacity and stable oxygen isotope composition can be used to estimate the timing of zone formations in otoliths. [source] Variations of sperm release in three batches of zebrafishJOURNAL OF FISH BIOLOGY, Issue 2 2004J. R. Kemadjou Njiwa By collecting and counting the number of sperm released during separate matings in three batches of zebrafish Danio rerio, aged 3,4, 4,5 and 5,6 months, males were observed to release sperm before the female started laying their eggs. After the female left the nest, the number and motility of sperm and life span of sperm of younger fish were higher than those of older fish in water samples collected under the nest and at the surface of the tank. Sperm were released in the form of sperm trails laid on the nest surface, subsequently active spermatozoa left the trails and moved in the water for several minutes. Sperm trails consisted of bands of viscous material in which the sperm were embedded. In most cases eggs were not laid directly over the sperm trail, suggesting that sperm may contact the eggs after the latter are released into the water. In all the three tested groups there was no significant difference (P > 0·05) between the number of sperm collected on some portions of the acetate sheets which lined the nest ceiling. This result demonstrated that the greater activity of younger fish accelerated the sperm dispersal in water. Male sperm duct glands, seminal vesicles, known to secrete mucosubstances are probably involved in the production of sperm trails. The possible influence of insemination on the mating style of zebrafish is discussed. [source] Comparison of testes structure, spermatogenesis, and spermatocytogenesis in young, aging, and hybrid cichlid fish (Cichlidae, Teleostei)JOURNAL OF MORPHOLOGY, Issue 3 2003Lev Fishelson Abstract Testis structure, spermatogenesis, and spermatocytogenesis were compared in 13 species of cichlid fishes, belonging to the subfamilies Haplochrominae and Tilapinae. The species studied were either mouth brooders, in which fertilization occurs mostly inside the mouth of the brooding fish, or substrate brooders, whose eggs adhere to a substrate over which the sperm is ejaculated. In this study, the embryogenesis of testes anlagen and sperm production was followed in embryos and in fish up to 15 years old, as well as in hybrids of the two subfamilies. In cichlids, the testes are of the unrestricted type and primary spermatogonia develop along the entire length of the developing sperm tubule. The first primary spermatogonia are observed in the testes anlagen 2,5 days after fertilization and they continue to develop in cysts formed by the enveloping Sertoli cells and the intertubular elements. The dimensions of such primary and secondary spermatocysts are correlated with the number of spermatogonia they contain and the corresponding number of mitotic multiplications. The largest mature cysts attained 300 ,m, and contained 2,200,2,400 spermatids in the mouth-brooding species and 2,600,3,200 in the substrate-brooding species. Despite the fact that in such cysts cytoplasmic bridges connect only the isogamete spermatids, the maturation of all cells and consequent spermiation is synchronized. Meristic characters distinguish the sperm of mouth brooders from those of substrate brooders, especially in the number of mitochondria and length of the flagellum. In older fish and hybrids, various changes can be seen in the gametogenic epithelium and intertubular cells. These include thickening of the connective tissue, formation of "yellow" groups of Leydig cells, cell apoptosis and degeneration, and, especially, formation of large spermatogonia, with large, electron-dense nucleoli, that have the cytological characteristics of oocytes. The intra- and interspecific variability of sperm dimensions in the studied cichlids poses an interesting question in the context of sperm competition. J. Morphol. 256:285,300, 2003. © 2003 Wiley-Liss, Inc. [source] | ||||||||||