The plant-based protein (PP) can negatively impact growth as well as fillet quality of fish due to the presence of anti-nutritional factors, imbalanced nutrient content, and low digestibility. Consequently, the incorporation of feed additives into PP feed holds promise in enhancing its utilization in fish and improving fillet quality. Thus, the objective of this study was to assess the effects of supplementing PP diets with two different types of additive mixtures on the growth, myogenic gene expression and fillet quality of rainbow trout (Oncorhynchus mykiss).
Materials and methods
Two thousand rainbow trout (2.22 g) were distributed in four groups with 5 replicates (100 fish/tank) and fed four isonitrogenous (42% CP) and isolipidic (20% lipid) diets namely fishmeal based diet as control (30% fish meal, FM), plant based diet (PP), PP+A1 ( PP supplemented with mixture of krill meal, taurine and organic selenium) and PP+A2 ( PP supplemented with mixture of proline, hydroxyproline and vitamin C). Fish were fed twice daily and six days a week at apparent satiation for 30 weeks. After end of the feeding trial, growth (weight gain, WG) and feed conversion ratio (FCR) were calculated. The relative expression of myogenic genes (myoblast determination protein 2 , MyoD2; m yogenic factor 5 , Myf5; and myocyte-specific enhancer-binding factor 2a , MEF2A ) were measured. The fillet quality parameters like texture profile analysis (TPA: hardness, cohesiveness, springiness, chewiness, and resilience ) and fillet color properties (lightness, L*; chroma , C*; and hue , ho) were measured. All the data were subjected to one-way analysis of variance (ANOVA) using General Linear Model in R-programming ( RStudio version 2023.06.0).
Results showed that dietary supplementation of additive mixtures in PP diets significantly (p < 0.05) improved the growth performance as compared to PP group without additive mixture and comparable to FM group (Figure 1a). Although there was no significant difference in FCR (0.83-0.87), the overall feed intake on PP group was lower than other groups. Hyperplasia related myogenic genes (MyoD2 and Myf5) were significantly (p < 0.05) up-regulated in the additive mixture supplemented groups (Figure 1b). Whereas no difference in hypertrophy related gene, MEF2A was observed between additive mixture supplemented groups and other groups. Fish fillet quality was also affected by additive mixture supplementation (T able 1), hardness of both additive mixture supplemented group s was higher than other groups, whereas cohesiveness of these groups were comparable to FM group. Fillet color properties showed that PP+A1 had higher value of C* and lower value of L* and ho as compared to other groups.
The supplementation of additive mixtures has been shown to ameliorate the negative impact of PP-based diets and improve the growth of rainbow trout. Furthermore, the up-regulation of myogenic genes (MyoD2 and Myf5) in the groups supplemented with the additive mixture supports its positive impact on growth and nutrient utilization, leading to enhanced muscle mass. The supplementation of additive mixtures has been found to improve fillet quality, particularly in terms of fillet hardness in both supplemented groups. Additionally, the fillet color properties were improved in the PP+A1 group compared to other groups. While previous studies have shown that the complete substitution of fish meal from various species does not have a negative impact on fillet quality during short-term culture periods (Kaushik et al., 1995), long-term feeding of a fish meal-free diet has been found to significantly reduce growth, as well as color properties and sensory quality in rainbow trout (De Francesco et al., 2004). In summary, the supplementation of additive mixtures in PP-based diets positively impacts the growth, muscle development, and fillet quality of rainbow trout.
De Francesco, Matilde, Parisi , G., Médale , F., Lupi , P., Kaushik, S. J., & Poli, B. M. (2004). Effect of long-term feeding with a plant protein mixture based diet on growth and body/fillet quality traits of large rainbow trout (Oncorhynchus mykiss). Aquaculture, 236(1–4), 413–429.
Kaushik, S. J., Cravedi , J. P., Lalles , J. P., Sumpter, J., Fauconneau , B., & Laroche, M. (1995). Partial or total replacement of fish meal by soybean protein on growth, protein utilization, potential estrogenic or antigenic effects, cholesterolemia and flesh quality in rainbow trout, Oncorhynchus mykiss. Aquaculture, 133(3–4), 257–274.