The effects of three commercial diets differing in protein and energy ratios on product quality of pike (Esox lucius)

This study investigated the effects of three different commercial diets on the growth, feed utilization, and product quality of pike (Esox lucius). The first diet had low lipid (12%) and low protein (37%) (diet A) content, the second diet had low lipid (12%) and high protein (52%) content (diet B), the third diet had higher lipid concentration (15%) and high protein content (52%) (diet C). Two hundred and seven pike were stocked in an experimental RAS (Recirculating Aquaculture System) and were fed ad libitum for the duration of the nine week trial. Specific growth rates, feed conversion rates, protein utilization, as well as body composition and somatic indices were calculated. Fish fed with diets B and C had significantly better SGR (Specific Growth Rate) and FCR (Feed Conversion Rate) than fish fed with diet A. The higher dietary lipid concentration does not cause significantly better protein utilization. Moreover, it had a negative effect on the product quality by increasing the body lipid concentration and the visceral fat deposition

Cryopreservation of European eel (Anguilla anguilla) sperm using different extenders and cryoprotectants

Experiments were carried out on the sperm cryopreservation of artificially induced eels. The effects of several extenders and two cryoprotectants on the motility of spermatozoa were investigated. The highest post-thaw motility was observed with the combination of Tanaka's extender and DMSO as cryoprotectant. Further dilution after thawing resulted in complete loss of motility in samples frozen in presence of DMSO while sperm frozen with methanol as cryoprotectant retained its motility after further dilution

Effect of graded dietary fish oil supplementation on body composition and fillet fatty acid composition of pike (Esox lucius L.)

A feeding experiment was conducted on northern pike, Esox lucius L. (123.6±33.3 g initial body weight) applying graded dietary fish oil supplementation resulting three dietary fat levels (without supplementation: 6.2% fat and 11.7, 17.4% fat levels with supplementations) in a recirculation system. Feed consumption, feed efficiency and protein utilization of pike was not affected by the treatment. Whole body lipid content analysis showed that the composition of pike was significantly affected by the increasing level of fish oil supplementation, although no relationship was detected between the dietary and the fillet lipid content, as well as the protein content of fish bodies. High docosahexaenoic acid (DHA, C22:6n-3) proportions were found in the muscle lipids (groups fed fish oil supplementation), as compared to the dietary fatty acid compositions suggesting that with dietary fish oil supplementation the dietary precursors (mainly EPA) enable pike to convert long chain highly unsaturated fatty acids, especially DHA; resulting high DHA: EPA ratios in the fillet

Attempts on artificial induction of sexual maturation of sterlet (Acipenser ruthenus) and identification of late spermatogenesis stage in hermaphroditic fish

Abstract Most of the 27 species of sturgeons are endangered or close to extinction which is connected to habitat degradation, water pollution and overfishing. Conservation programmes are facing the problem of late maturation which can be reached between 5 and 11 years depending on the species and gender. The aim of our study was to investigate the possibility of shortening the sexual maturation using hormonal administration, and measure the blood serum hormone content to distinguish different genders and maturation stages. There was no effect of a 20-week-long hormonal treatment (10 mg carp pituitary/bodyweight kg/week) on the sexual maturation. The number of females was relatively high (67.6% n = 23) and the number of males was relatively low (11.8%, n = 4). Moreover, the number of hermaphroditic fish was surprisingly high (20.6%, n = 7) and appeared independently from hormone administration. Hermaphroditic fish had fully developed spermatozoa and could be distinguished by the increased level of testosterone hormone in blood serum