Effect of Temperature on Energy Budgets in Triploid Turbot Juveniles, Scophthalmus maximus

Abstract

The investigation of fish bioenergetics primarily relies on using an energy budget equation to examine how the allocation of energy and nutrients in their diet impacts their growth rate and reproductive capabilities. By accurately forecasting the distribution of feeding intake energy towards growth, fecal excretion, and metabolism within the overall energetic framework of a fish, and considering diverse physiological factors or ecological influences that affect each aspect of this energetic balance sheet, scientific discoveries derived from these studies can provide valuable insights for making informed decisions regarding optimal dietary choices to enhance fish well-being. Additionally, it aids in refining rearing management strategies leading to improved feed utilization efficiencies, ultimately resulting in more sustainable aquaculture practices aimed at minimizing environmental pollution caused by excessive feeding activities. Temperature affects various physiological processes and growth potential, thereby, influencing feed requirements and utilization efficiency, which ultimately determine the allocation of feeding intake energy among growth, fecal, excretory, and metabolic energies. Extensive studies have been conducted to explore how temperature influences fish growth rates along with their overall energy budgets. The effects of temperature on the growth and energy budgets in triploid turbot, Scophthalmus maximus, were investigated in this study by establishing a series of five temperature gradients (13 ℃, 16 ℃, 19 ℃, 22 ℃, and 25 ℃). Measurements of the growth and energy budget allocations were conducted on large-sized triploid turbot juveniles with mean body weight of (120.24±17.20) g at the aforementioned temperatures for 49 d. The results indicate that under conditions of salinity 28.6, pH 7.8, dissolved oxygen content above 7.8 mg/L, light intensity of 300 lx, and a light period of 16 L∶8 D ratio; the feeding rates (FR) and weight gain rates (WG) of triploid juveniles initially increased with increasing temperature before declining, with the peak FR of (1.02±0.06)% and (0.95±0.04)% observed at 19 ℃ and 22 ℃, respectively, whereas the highest WG was recorded at 19 ℃ (62.17±3.10)% (P < 0.05). The relationship between specific growth rate (SGR) or feed conversion efficiency (FCE) and temperature, calculated based on different parameters including wet weight (SGRw and FCEw), dry weight (SGRd and FCEd), protein content (SGRp and FCEp), and energy content (SGRe and FCEe), was observed to follow a quadratic regression equation. The highest recorded temperature for the SGR values was observed at 19 ℃. At 25 ℃, the group exhibited significantly reduced levels of SGRs compared to that of other experimental groups, except for the data recorded at 13 ℃ (P < 0.05), where 13 ℃ and 25 ℃ showed relatively low SGR values. Additionally, no significant differences were observed in SGR values between 16 ℃ and 22 ℃. The maximum FCE values were also attained at 19 ℃ (P < 0.05). In contrast, the FCE values recorded at 13 ℃ and 25 ℃ exhibited considerable reductions when compared to those obtained from other experimental groups (P < 0.05). Regression analysis revealed that the optimal temperatures for SGRw, SGRd, SGRp, and SGRe were determined as 18.4 ℃, 18.7 ℃, 18.9 ℃, and 18.5 ℃, respectively, whereas the temperatures for achieving maximum FCEw, FCEd, FCEp, and FCEe were 18.1 ℃, 18.6 ℃, 18.9 ℃, and 18.2 ℃, respectively. Additionally, the rates of nitrogenous excretion and fecal production exhibited an initial decrease followed by an increase with increasing temperature, reaching their highest levels at 25 ℃. Dry matter, protein, and energy apparent digestibility coefficients at 25 ℃ were significantly lower than those observed at other temperatures. The feeding intake energy and growth energy proportion demonstrated an inverted "U" shape with increasing temperature, reaching its highest value at 19 ℃. The allocation of energy in triploid juveniles was primarily dominated by growth and metabolism energies, whereas the proportion of metabolism energy to feeding intake energy displayed a "U" shape trend with increasing temperature. The proportion of growth energy to feeding intake energy ranged from 17.86% to 34.58%, whereas the proportion of fecal energy varied from 4.12% to 5.57%. Furthermore, the proportion of excretion energy to feeding intake energy ranged from 6.61% to 9.19%, and metabolism energy accounted for 54.69% to 67.38% of feeding intake energy. The energy budget equation of triploid turbot juvenile at 19 ℃ was 100.00 C (feeding intake energy) = 34.58 G (growth energy) +4.12 F (fecal energy) +6.61 U (excretion energy) +54.69 R (metabolism energy) or 100.00 A (assimilated energy) = 38.74 G+61.26 R. The triploid turbot juveniles exhibited an energy allocation pattern characterized by high growth efficiency and low metabolic consumption. Consequently, the optimal rearing temperature for triploid turbot juveniles with an average weight of 120 g ranged from 18.1–18.9 ℃. These findings offer valuable insights into optimizing aquaculture conditions, improving feed efficiency, and controlling water environment pollution in the context of triploid turbot farming.

Keywords

• scophthalmus maximus
• triploid juveniles
• temperature
• energy budget