Size-dependent effects of daily thermal fluctuations on the growth and size heterogeneity of Nile tilapia Oreochromis niloticus.
The growth of Nile tilapia Oreochromis niloticus (0.02-20.00 g) was measured when fed to excess during the hours of light, following their exposure to five thermal regimes fluctuating around the thermal optimum for growth (T(opt) = 30 degrees C) over the diel cycle of day (light, L) and night (dark, N), i.e. 27 degrees C(L):33 degrees C(N), 28.5 degrees C(L):31.5 degrees C(N), 30 degrees C(L):30 degrees C(N), 31.5 degrees C(L):28.5 degrees C(N) and 33 degrees C(L):27 degrees C(N) (two replicates per treatment, six weeks' rearing, growth measurements at weekly intervals). A model constructed with a stepwise multiple-regression analysis accounted for 87.4% of the variation of the specific growth rate (G, % M day(-1)) from the variations of wet mass (M), the extent of the thermal fluctuation (F(T)) and their interactions, i.e. log(10)G = 1.7686 - 0.2136 log(10)M + 0.0806 [log (10)Mx log (10) (1 + F(T))] - 0.0394 [log(10)Mx log (10) (1 + F(T))](2). Based on this model, the thermal fluctuation that produces the fastest growth ( , degrees C) decreases in a curvilinear way, from 5.1 degrees C at 20 mg to c. 0.7 degrees C at 20 g. Thermal regimes that produce the slowest growth also produce the highest size heterogeneity. Functional hypotheses behind the size-dependent effects of thermal fluctuations are discussed, together with their implications in natural habitats and aquaculture systems with in different contexts of food availability.
Azaza
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INSTM, Laboratoire d'Aquaculture, 28 Rue 2 mars 1934, Salammbô, Tunisia. med.azaza@instm.rnrt.tn
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Kraiem
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D000818:Animals; D049628:Body Size; D023681:Cichlids / Q000254:growth & development*; D012044:Regression Analysis; D013696:Temperature