Thermal preference of juvenile Dover sole (Solea solea) in relation to thermal acclimation and optimal growth temperature

Abstract

Dover sole (Solea solea) is an obligate ectotherm with a natural thermal habitat ranging from approximately 5 to 27°C. Thermal optima for growth lie in the range of 20 to 25°C. More precise information on thermal optima for growth is needed for cost-effective Dover sole aquaculture. The main objective of this study was to determine the optimal growth temperature of juvenile Dover sole (Solea solea) and in addition to test the hypothesis that the final preferendum equals the optimal growth temperature. Temperature preference was measured in a circular preference chamber for Dover sole acclimated to 18, 22 and 28°C. Optimal growth temperature was measured by rearing Dover sole at 19, 22, 25 and 28°C. The optimal growth temperature resulting from this growth experiment was 22.7°C for Dover sole with a size between 30 to 50 g. The temperature preferred by juvenile Dover sole increases with acclimation temperature and exceeds the optimal temperature for growth. A final preferendum could not be detected. Although a confounding effect of behavioural fever on temperature preference could not be entirely excluded, thermal preference and thermal optima for physiological processes seem to be unrelated in Dover sole.

Figure 1. Schematic presentation of the preference chamber.

Top view (A) presents schematically the water flows (arrows) and the main elements: 1) water inflow, 2) mixing channel, 3) swimming channel, 4) effluent channel, 5) central section with water drain. Top view (B) presents schematically the temperature gradient in the preference chamber.

Figure 2. Water temperatures in the preference chamber during the preference tests for the three acclimation temperatures.

Mean (SD, n = 6) water temperatures in the five temperature zones during the non-gradient observation, installation of the temperature gradients and acute preference observations are presented for the tests conducted with fish acclimated to 18°C (A), 22°C (B) and 28°C (C). Water temperatures during the 24 h preference observation equalled the water temperatures during the acute preference observations (not shown).

Figure 3. Water temperatures during the growth experiment.

For each temperature treatment the mean (SD, n = 2) water temperature during the acclimation, installation of temperatures and the experiment is presented. Overall mean temperature per treatment during the experiment (n = 26) differed significantly among all treatments (ANOVA, p<0.0001).

Figure 4. Fish distribution over the preference chamber.

Fish distributions during non-gradient, acute preference and 24 h preference observations are expressed as odds ratios (proportion of temperature zones used dived by the proportion of temperature zones available) and are presented for fish acclimated to 18°C (A), 22°C (B) and 28°C (C). Fish distribution was non-random during all non-gradient observations (MANOVA, p = 0.002) without differences among temperature acclimation treatments (MANOVA, p = 0.42). Fish distribution observed during acute preference observations differed significantly from the non-gradient observations (MANOVA, p<0.001). Fish distribution during 24 h preference observations differed significantly from the non-gradient (MANOVA, p<0.0001) as well as the acute preference observations (MANOVA, p<0.002). Among acclimation temperature treatments fish distribution differed during acute preference observations (MANOVA, p = 0.01) but not during the 24 h preference observations (MANOVA, p = 0.21).

Figure 5. Cumulative food intake of juvenile Dover sole (S. solea) in relation to water temperature.

Mean (SD, n = 2) cumulative food intake during acclimation, installation of temperatures and the experimental period are presented per water temperature treatment.

Figure 6. Total feed intake and specific growth rate of juvenile Dover sole (S. solea) in relation to water temperature.

Total feed intake (A) (TFI, g/fish) peaks at 22.5°C. Total feed intake (g/fish) TFI = −1.111.T²+50.T−498 (polynomial regression analysis, model p-value = 0.012, r² = 0.77). Specific growth rate (B) (SGR, %/d) peaks at 22.5°C. SGR = −0.044.T²+1.99.T−19.5 (polynomial regression analysis, model p-value = 0.002, r² = 0.89). T = water temperature (°C).

Figure 7. Predicted and measured relations between acclimation temperature and preferred temperature for juvenile Dover sole (S. solea).

For fish in category 1 the preferred temperature increases with acclimation temperature until they equal each other at the final preferendum. Beyond the final preferendum, here set at the measured optimal growth temperature, the preferred temperature stabilises. For fish in category 2 the preferred temperature is independent from the acclimation temperature and lies close to the final preferendum and optimal growth temperature. The measured acute preference increases with acclimation temperature.