This study investigates the dietary arachidonic acid (ARA) requirement from juvenile to maturation stage in an anabantid model fish, the blue gourami, Trichopodus trichopterus. Specifically we determined the optimum dietary ARA content to maximize juvenile growth and subsequent sexual maturation and to improve the quality of their eggs and offspring. Five experimental diets containing 0.02, 0.53, 1.05, 1.60, and 2.12% ARA (of dry weight) were fed to juveniles over 5 mo. The results showed that whole‐body fatty acid profile of broodstock significantly changed in fish fed diets of different ARA content (ANOVA, P < 0.003). The highest contents of 18:2n‐6 and Σn‐6 were obtained in fish fed 0.53% ARA, and a decreasing trend was observed with elevated dietary ARA levels. Monthly specific growth rate (SGR) measurements revealed significant differences in the juvenile stage, but the SGR of broodstock was unaffected by dietary ARA. Protein and ash content of whole‐body broodstock showed no differences among groups, while lipid content decreased as ARA levels increased. Maximum volume of the oocyte was obtained in the 1.05% ARA group, while the yolk sac size increased as dietary ARA increased. The optimum growth and survival of the larvae produced by broodstock were recorded in the 2.12 and 1.6% ARA groups, respectively. It was concluded that despite the presumed ability of freshwater fish to synthesize and meet their highly unsaturated fatty acid requirements, dietary ARA higher than 1.05% had significant stimulatory effects on growth of juveniles but no obvious influence on the growth of matured fish. Also, higher ARA levels (1.6–2.12%) were found to improve the quality of eggs and offspring.
The experiments were conducted to examine the effects of five photoperiod regimes (24:00; 16:08; 12:12; 08:16 and 00:24 hours) (Light: Dark) on reproductive traits, development and generation time, survival rate, adult sex ratio and total life span of freshwater cyclopoid copepod, Mesocyclops sp.. Daily offspring production of individual female was monitored from the last moulting until death of all females. Mean daily offspring production affected by photoperiod, with the highest output recorded at 08:16, which was significantly higher than 24:00 and 00:24, but not differ from 12:12 and 16:08. No significant differences were obtained in total egg sacs per female among treatments. Photoperiods other than 12:12 significantly prolonged the inter‐clutch times. A trend of accelerated development and generation time was shown with increasing illumination periods. With the exception of female's life span, the survival rates of offspring and females as well as adult sex ratio were not significantly affected by photoperiod. Based on results of this study, it is recommended that Mesocyclops sp. can tolerate and reproduce in a wide range of photoperiod regimes, however, photoperiod of 08:16 being adopted in controlled culture due to its high reproductive performance, fast development and long longevity.
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