In a long-term growth trial, transgenic tilapia Oreochromis niloticus L. showed a 2·5-fold increase in growth compared with non-transgenic siblings. At 7 months, mean mass of transgenic tilapia was 653 g compared with 260 g for non-transgenic siblings. A significant increase (P<0·01) in head : total length ratio, viscera-somatic index and hepato-somatic index was observed in transgenic fish. Female gonado-somatic index (I G ) was found to be lower in transgenics than non-transgenic siblings in both mixed and separate culture conditions. Transgenic male I G values were found to be higher in mixed culture and lower in separate culture than that of their non-transgenic siblings. Food conversion efficiency was more than 20% greater in the transgenic fish. In a second shorter-term growth performance trial, the transgenic fish grew to about four times the size of their non-transgenic siblings. A digestibility trial suggested that transgenic tilapia were more efficient utilizers of protein, dry matter and energy. Apparent digestibility of protein and apparent energy digestibility were higher in the transgenic fish. 2001 The Fisheries Society of the British Isles
Nine trials were carried out on the induced propagation of pike perch in out-of-season as well as in the natural reproduction period. From January till May, periodically, 16^20 pairs were transported to the hatchery, and acclimated to 15^16 1C. The following hormonal treatments were used to induce reproduction: carp pituitary homogenate (CP) and human chorionic gonadotropin (hCG) alone or in combination; gonadotrop-releasing hormone 'Ovurelin' (D-Phe 6 -LH-RH) alone or with metaclopramid (MTC); and 'Ovopel' [containing des-Gly 10 -(D-Ala 6 )-LH-RHethylamide and MTC]. The e¡ects of daylight regime, water temperature and the length of the pre-spawning conditioning period on the reproduction performance were determined. From the 130 hormonally treated pairs, 122 either spawned in tanks or were stripped. There were no di¡erences in the ovulation rate between out-of-season (93%) and seasonal (91%) propagation. The developmental stage of the eggs correlated with the latency period, which signi¢cantly declined from January till April. The latency period was the shortest in ¢sh treated with hCG and, secondly, with CP. The germinal vesicle migration did not proceed without hormonal treatment, although in some trials breeders were kept at the spawning temperature for12weeks. The results demonstrate that the pike perch can be successfully induced to spawn about 3 months earlier than its natural spawning season, which allows a signi¢cantly prolonged yearly supply of fry. Ã Females that did not respond until D7 received a third treatment.wAt D2 seven ¢sh received a third CP injection. zSix pairs were kept at 15.0^15.3 1C, and other seven pairs at 18.0^18.2 1C. ‰Four pairs were kept in 12 h light:12 h dark, and ¢ve pairs in 24 h darkness. zUp from D2 attempts were made to strip the ¢sh at 4-h intervals. hcg, human chorionic gonadotropin; CP, carp pituitary.
Indoor propagation of pike perch A Ro¤ nyaiValues within the columns with di¡erent superscripts are signi¢cantly di¡erent (Po0.05).
This study aimed to determine the effect of feeding rates and water temperatures on the growth, feed utilization and size heterogeneity changes in subadult pikeperch. Fish with an average weight of 84±19 g were fed with a commercial trout diet for 18 weeks at a water temperature of 20 °C and 25 °C. Four feeding rates (PSFR) were predicted at both temperatures, which corresponded to 1.0%, 1.25%, 1.50% and 2.0% of body weight per day (bw day−1) for the first, and to 0.8%, 1.0%, 1.2% and 1.4% of bw day−1 for the second 9 weeks respectively. At the end of the experiment, the individual weight averaged 273±82 g. Pikeperch showed a better growth rate [specific growth rate (SGR)] and apparent feed conversion rates (AFCR) at the higher temperature. Thermal‐unit growth coefficient (TGC) was better at the lower temperature. The values of SGR, TGC and AFCR significantly increased with increasing PSFR at both temperatures. The values of TGC plotted against the computed feeding rates allowed estimation of the maximum feeding rates (1.25% and 1.15% of bw day−1 for pikeperch of 150–180 g at 25 and 20 °C respectively). Size heterogeneity changes were affected neither by the feeding rate nor by temperature.
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