INCLUSION EFFECTS OF JACK MACKEREL MEAL IN DIETS REPLACING 50% OF FISH MEAL WITH FREEZE-DRIED POLLOCK BY-PRODUCT MEAL ON THE GROWTH PERFORMANCE AND FEED AVAILABILITY OF OLIVE FLOUNDER Paralichthys olivaceus, AND ECONOMIC ANALYSIS

Introduction & Methodology

The low-fish meal (FM) diets commonly cause reduced palatability and decreased feed consumption (FC), eventually impairing gowth performance of fish (Hussain et al., 2024). Our previous study (Jeong et al., 2020) revealed that jack mackerel meal (JMM) exhibited the greatest feeding attractant response to olive flounder among 15 protein feed ingredients including various FMs and crustacean meals. Therefore, this study aims to evaluate the inclusion effects of JMM in diets replacing 50% of FM with freeze-dried pollock by-product meal (FPBM) on the growth performance and feed availability of olive flounder, and economic analysis. A total of 525 juvenile (averaging 6.3 g) fish were randomly distributed into 21 of 50-L flow-through tanks (25 fish/tank). Seven isoproteic (52.5%) and isolipidic (12.0%) diets were formulated. The control (Con) diet contained 60% FM. In the Con diet, 50% of FM was replaced with FPBM, and then increased levels (0%, 10%, 20%, 30%, 40%, and 50%) of JMM were included at the expense of FM, named as the FJ0, FJ10, FJ20, FJ30, FJ40, and FJ50 diets, respectively. All experimental diets were assigned to triplicate groups of fish. Fish were hand-fed twice a day for 50 days until visual satiation was reached.

Results & Discussion

At the end of the 50-day feeding trial, weight gain (WG) and specific growth rate (SGR) of fish fed the FJ40 and FJ50 diets were significantly (P < 0.0001 for both) higher than those of fish fed the FJ0, FJ10, and FJ20 diets, but not significantly (P > 0.05) different from those of fish fed the Con diet (Fig. 1). In orthogonal polynomial contrast, WG and SGR of fish revealed linear (P < 0.0001 for both) relationships with dietary inclusion levels of JMM in the low-FM diets replacing 50% of FM with FPBM. In regression analysis, linear models were determined to be the most suitable models between inclusion levels of JMM in diets replacing 50% of FM with FPBM versus WG (Y = 1.174333X + 14.1832, P < 0.0001, Adj. R² = 0.8840) and SGR (Y = 0.000946X + 0.0239, P < 0.0001, Adj. R² = 0.7988), respectively. FC of fish fed the FJ50 diet was significantly (P < 0.0001) higher than that of fish fed the FJ0 and FJ10 diets, but not significantly (P > 0.05) different from that of fish fed the Con diet (Fig. 2). In orthogonal polynomial contrast, FC of fish revealed linear (P < 0.0001) relationship with dietary inclusion levels of JMM in the low-FM diets. In orthogonal polynomial contrast, FC of fish revealed linear (P < 0.0001) relationship with dietary inclusion levels of JMM in the low-FM diets. In regression analysis, linear model was determined to be the most suitable model between inclusion levels of JMM in the low-FM diets versus FC (Y = 0.791677X + 15.3158, Adj. R² = 0.7357, P < 0.0001). Economic profit index (EPI) of fish fed the FJ40 and FJ50 diets was significantly (P < 0.0001) higher than that of fish fed the FJ0, FJ10, and FJ20 diets, but not significantly (P > 0.05) different from that of fish fed the Con diet. In orthogonal polynomial contrast, EPI of fish revealed linear (P < 0.0001) relationship with dietary inclusion levels of JMM in the low-FM diets. In regression analysis, linear model was determined to be the most suitable model between inclusion levels of JMM in low-FM diets versus EPI (Y = 0.003857X + 0.7797, Adj. R² = 0.8999, P < 0.0001). However, feed utilization (feed efficiency, protein efficiency ratio, and protein retention), biological indices, chemical composition, and amino acid profiles of fish were not significantly affected by dietary treatments. Incorporated 30–50% JMM as a feed enhancer in the low-FM diets replacing 50% of FM with FPBM achieved comparable WG, SGR, and FC to fish fed the Con diet. Furthermore, the FJ50 diet led to the highest EPI to farmers. In conclusion, the FJ50 diet seems to be the most recommended strategy for olive flounder farmers in terms of the highest EPI.

Figure

Fig. 1. Weight gain (WG, g fish^-1) (Polynomial orthogonal contrast; Linear = 0.0001, Quadratic = 0.1218, Cubic = 0.5018) (Regression analysis; Y = 1.174333X + 14.1832, Adj. R² = 0.8840, P < 0.0001) and specific growth rate (SGR, % day^-1) (Linear = 0.0001, Quadratic = 0. 0936, Cubic = 0.5018) (Y = 0.000946X + 0.0239, Adj. R² = 0.7988, P < 0.0001) of olive flounder fed the experimental diets for 50 days (means of triplicate) (P < 0.0001 for both).

Fig. 2. Feed consumption (FC, g fish^-1) (Linear = 0.0001, Quadratic = 0.0663, Cubic = 0.7774) (Y = 0.791677X + 15.3158, Adj. R² = 0.7357, P < 0.0001) and economic profit index (EPI, USD fish^-1) (Linear = 0.0001, Quadratic = 0.1062, Cubic = 0.4563) (Y = 0.003857X + 0.7797, Adj. R² = 0.8999, P < 0.0001) of olive flounder fed the experimental diets for 50 days (means of triplicate) (P < 0.0001 for both).

Acknowledgment

This research was supported by Korea Institute of Marine Science & Technology Promotion (KIMST) funded by the Ministry of Oceans and Fisheries (Grant 2025-KIMST-2026000016 and RS-2018-KS181194).

References

Hussain, S.M., Khurram, F., Naeem, A., Shah, S.Z.H., Sarker, P.K., Naeem, E., Arsalan, M.Z., Riaz, D., Yousaf, Z., Faisal, M., Amjad, M., (2024) Can animal by-products replace fishmeal A review on substitution of fishmeal with different animal protein sources. International Aquatic Research. https://doi.org/10.22034/iar.2024.1996466.1517.

Jeong, H.S., Choi, D.G., Lee, K.W., Cho, S.H., Lim, S.G., Lee, B.J., Hur, S.W., Son, M.H., Lee, S.H., Kim, K.W., (2020) Attractiveness of various crude feed ingredients to juvenile olive flounder (Paralichthys olivaceus, Temminck & Schlegel) and its application to aquaculture. Aquaculture Research. 51 4517–4532. https://doi.org/10.1111/are.14797.