Introduction
In Central European aquaculture, carp shows active and inactive periods depending on weather conditions of the winter season, however as a result of its activity, it often loses weight (Lukowicz & Gerstner, 1998). Feeding occurs from around 6°C and increases with rising temperatures (Terhes, 2025; Chen Song-bo et al., 2012). During milder winter periods, controlled feeding may help maintain body condition and reduce weight loss, supporting healthier stocks till spring. Accordingly, we aimed to determine the requirement for digestible energy and protein for juvenile fish in winter feeding period.
Materials and Methods
Four diets for carp yearlings were formulated and produced by Garant Ltd., Austria. The diets differed in their digestible protein and digestible energy ratios (DP/DE (g/MJ): Diet 1: 18.6; Diet 2: 15.4; Diet 3: 13.8; Diet 4: 11.4). Winter wheat was included as a negative control diet, as it is still commonly used by farmers. The feeding trial lasted over 55 days in three replicate tanks in RAS with initial body weight 99.5 ±13.8 g and with stocking density 35 fish/m3. Based on previous results 1% of feeding rate (per biomass) was set at constant 10°C. At the end of the feeding trial fish were individually weighed to determine the final body weights in each tank. In addition, Fulton index (condition factor-CF); hepatosomatic index (HIS); viscerosomatic index (VSI); intraperitoneal fat index (IPI) was calculated. The trial continued with the remaining fish population at 20 °C temperature. The stocking density was 19 fish/m3 (~2.2 kg/m3). All the groups were fed with Diet 1 in the feeding rate 3% of biomass. At the end of this 43 days trial growth performance and nutrient utilization parameters were assessed.
Results and Discussion
During the low temperature (10°C) period, the fish consumed and utilized the formulated diets. Body weight increased by 22–27% across treatments, except for Diet 5 (wheat), where only a 5.67% growth was observed. The feed conversion ratio ranged between 1.97 and 2.37, again with the exception of Diet 5, which showed a markedly higher value (10.3). According to the production and nutrient utilization parameters evaluated, Diet 4 showed the best overall performance. However, differences among treatments were not statistically significant for most parameters. The diet with the highest digestible protein-to-digestible energy ratio (Diet 1), performed the worst and exhibited a significantly lower protein efficiency ratio compared to Diet 4. Based on these findings, it seems lower protein and higher energy content is preferable, with an optimal digestible protein-to-digestible energy ratio of approximately 11.44 MJ/kg.
Following the trial mimicking an overwintering feeding regime, the fish were subsequently fed with standard diet (Diet 1), at constants 20 °C temperature. During this period, the fish that had previously been fed wheat (Diet 5) exhibited rapid and intensive growth, which resulted in performance comparable to the other treatments in terms of SGR, FCR, PER, and LER. It appears that the growth potential of this group was also high at 20 °C, compensating the week growth performance in the overwintering period. When comparing the performance of the fish fed formulated diets, significant difference in nutrient utilization was observed between Diet 3 and Diet 4 at 10°C, Diet 4 performed best.
Conclusions
Overall, the performance of the formulated diets was considered highly acceptable and differed significantly from the treatment in which the traditional feeding method was applied. Furthermore, it was demonstrated that lower protein and higher energy content is preferable, with an optimal digestible protein-to-digestible energy ratio of approximately 11.44 MJ/kg.
Acknowledgements
This research was supported by Horizon EU programme ACTFast GA 101181159
The experimental work was supported by the Research Excellence Program of MATE.
References
Lukowicz, M., P. Gerstner. (1998) H��ltern und Wintern Lehrbuch der Teichwirtschaft. Berlin: Parey 495-503.
Song-bo, Ch., Chen W. & Fan, Zh. (2012) Effect of water temperature on feeding rhythm in common carp (Cyprinus carpio haematopterus Temminck et Schlegel). J. of Northeast Agr. Univ. 19,1, 57-61
Terhes, A., W��ber, Cs., Nagy Z., J. S��ndor, Zs. (2025) Determination of the temperature minimum for feed intake in common carp Cyprinus carpio epostersAE2025AbstractBoook 1777-1778