Influence of daylength on growth, heterogeneity, gonad development, sexual steroid and thyroid levels, and N and P budgets in Perca fluÕiatilis

A 4-month study was conducted to determine the influence of daylength on growth, heterogeneity, gonad development, sexual steroid and thyroid levels, and N and P budgets in Eurasian Ž . Ž . perch juveniles Perca fluÕiatilis . Fishes mean weight: 5.1 g were reared in tanks in recirculaty3 Ž . ing systems at an initial biomass of 1 kg m under three different daylengths DL , 12, 18, and 24 h, including a simulated dawn and dusk phase. Perch were fed by demand feeders. Growth was Ž . checked monthly 100 fish per tank , carcass analyses and sex determinations were made on an average of 20 fish per tank with at least five small, five medium and five large fish. The increase Ž of DL, from 12, 18, or 24 h, induced significantly higher specific growth rates 1.78"0.17% day and 1.77"0.06% day for the 18and 24-h groups, respectively, vs. 1.36"0.12% y1 . day for the 12-h group . After 112 days, a lower coefficient of variation in weight was found in Ž . Ž the 12-h group 40.3"2.6% , compared to the 18and 24-h groups 50.2"6.6% and 54.1"4.1%, . Ž respectively . However, continuous daylight decreased survival in a significant way 76.0"7.4% . for the 24-h group, vs. 89.0"3.2% and 88.2"3.3% for the 12and 18-h groups, respectively . The increase of DL from 12, 18, and 24 h also inhibited gonad development, especially in males. ) Corresponding author. Tel.: q33-3-83-30-28-41; fax: q33-3-83-32-30-16. Ž . E-mail address: [email protected] P. Fontaine . 0044-8486r00r$ see front matter q 2000 Elsevier Science B.V. All rights reserved. Ž . PII: S0044-8486 99 00357-9 ( ) S. Jourdan et al.rAquaculture 186 2000 253–265 254 However, for females and males, there was no significant DL effect on plasma sexual steroids and thyroid hormones levels. Likewise, no DL effect on N and P retention and loss was found. From this study, it appears that manipulating DL is a promising tool for improving rearing performance of Eurasian perch. q 2000 Elsevier Science B.V. All rights reserved.