Introduction
Fish feed are produced primarily with plant ingredients with minimal amount of fish meal possible. While this helps reduce feed cost, it is equally important not to compromise on the nutritional quality of feed and thus, the fish performance. For example, animal ingredients contain certain amount of creatine or its precursor, whilst the plant based ingredients contain no creatine. Creatine and its phosphorylated form phosphocreatine (PCr ) play a vital role in the cellular energy metabolism of animals. The adenosine triphospate (ATP)–creatine phosphate system transfers a high-energy phosphate from PCr to adenosine diphosphate (ADP) to regenerate ATP. Creatine is synthesized in body by its precursor guanidinoacetic acid (GAA) which is more stable under feed production process than the creatine itself. There are studies showing the positive benefits of dietary GAA supplementation in fish including tilapia (e.g., Aziza et al. 2020; Mabrouk et al. 2020) and carp (Yang et al. 2021). Borchel et al. (2014) showed the importance of creatine on the energy metabolism of rainbow trout. The ob jective of this study was to investigate the effects of increasing levels of GAA supplementation on the performance of juvenile rainbow trout.
Materials and Methods
Experimental basal diet (D1) was formulated with low levels of fish meal (5%) but still meeting the known recommended nutrient levels for rainbow trout. Diets 2-7 were supplemented with increasing levels of GAA at 0.04% increment levels (0.04-0.24%) whilst the Diet 8 was supplemented with the GAA source at 0.30%. All the 8 diets were allotted randomly to the 32 experimental tanks, containing 30 fish (~9 g, mean initial body weight) per tank and giving 4 replicate tanks per diet. Fish were fed 4 times a day over a 98-day study period, which included 90 feeding days and 8 no-feed days (fish were not fed during the weighing days).
Results
At the end of the study (day 98) mean body weight had increased to 143- 158 g among the dietary groups and differed significantly (p < 0.05, ANOVA) . Diets supplemented with 0.04 and 0.08 % GAA showed a significantly higher body weight gain compared with the basal group (p < 0.05, ANOVA). In terms of growth, fish fed diets supplemented 0.04-0.12% GAA showed significantly better thermal growth coefficient whilst only the 0.08% GAA supplemented diet produced significantly better specific growth rate compared with the basal. Feed conversion rate of fish fed different treatment diets ranged from 0.97 to 1.00 and showed no difference. On the initial and final day, no differences were detected on the whole-body proximate nutrient composition of rainbow trout, however, fish group fed with 0.08% and 0.12% GAA supplemented diet showed marginal increase in the body protein gain compared with the control group (0.05 < p < 0.10%, ANOVA) . Overall, our study results clearly indicate that supplementing low-fish meal rainbow trout feed at 0.08 % GAA significantly improves the fish growth performance.
References
Aziza A, Mahmoud R, Zahran E, Gadalla H. 2020. Dietary supplementation of guanidinoacetic acid improves growth, biochemical parameters, antioxidant capacity and cytokine responses in Nile tilapia ( Oreochromis niloticus). Fish Shellfish Immunol. 97: 367-374. doi: 10.1016/j.fsi.2019.12.052.
Borchel , A., M. Verleih , A. Rebl , C. Kühn and T. Goldammer (2014) Creatine metabolism differs between mammals and rainbow trout (Oncorhynchus mykiss) SpringerPlus 3: 510
Mabrouk, M. M., A. F. B. Abdelhamid, A. G. A. Gewida , H. A. M. Abo-State. 2020. Effects of Creatine and Guanidinoacetic Acid as Feed Additives on Nile Tilapia (Oreochromis niloticus) Growth Performance. Journal of Animal and Poultry Production. 11(4): 143-147.
Yang, L.L., Wu, P., Feng, L., Jiang, W.D., Liu, Y., Kuang , S.Y., Zhou, X.Q., 2021. Guanidinoacetic acid supplementation totally based on vegetable meal diet improved the growth performance, muscle flavor components and sensory characteristics of on-growing grass carp (Ctenopharygodon idella). Aquaculture 531, 735841. https://doi.org/10.1016/j.aquaculture.2020.735841.