INFLUENCE OF DAYLENGTH ON GROWTH, HETEROGENEITY, GONAD DEVELOPMENT, SEXUAL STEROID AND THYROID LEVELS, AND N AND P BUDGETS IN PERCA FLUVIATILIS
S. Jourdan, P. Fontaine, T. Boujard, E. Vandeloise, J.N. Gardeur, M. Anthouard, P. Kestemont-2000
Aquaculture, 186 (3-4): 253-265
Abstract:
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 perch juveniles (Perca fluviatilis). Fishes (mean weight: 5.1 g) were reared in tanks in recirculating systems at an initial biomass of 1 kg/m3 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 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 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 18- and 24-h groups, respectively, vs. 1.36 +/- 0.12%/day for the 12-h group). After 112 days, a lower coefficient of variation in weight was found in the 12-h group (40.3 +/- 2.6%), compared to the 18- and 24-h groups (50.2 +/- 6.6% and 54.1 +/- 4.1%, 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 12- and 18-h groups, respectively). The increase of DL from 12, 18, and 24 h also inhibited gonad development, especially in males. 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.
(Laboratoire de Sciences Animales, INPL-UHP Nancy 1, MAN, 34 rue Sainte-Catherine, 54000 Nancy, France)