Effects of substituting fish meal with Chlorella meal on growth performance, whole-body composition, pigmentation, and physiological health of marbled eel ( Anguilla marmorata )

Chlorella meal is considered a promising alternative to fish meal in aquafeeds, but the effects of incorporating Chlorella meal as a feed ingredient on the growth and quality of eel have not been explored. The effects of partially substituting fish meal (0 %, 5 %, 10 %, 15 %, and 20 %) with Chlorella meal on the growth performance, whole-body composition, pigmentation, and physiological health of marbled eel (Anguilla marmorata) were evaluated in this study. The results revealed that dietary inclusion of Chlorella meal significantly increased the final body weight (FBW), weight gain rate (WGR), and specific growth rate (SGR), but it significantly decreased the feed conversion rate (FCR), with these parameters exhibiting linear trends (P < 0.05). The whole-body protein and fat contents were significantly higher in all groups fed with diets containing Chlorella meal compared to the control group (P < 0.05). In addition, the dorsal and abdominal skin of marbled eel exhibited an orange-yellow color, and the color intensity increased with increasing levels of dietary Chlorella meal. The color change corresponded to increased values of a* (redness), b* (yellowness), and lutein content in the fish skin (P < 0.05). The physiological health of marbled eel also improved in the groups where Chlorella meal was included. The optimal replacement rate was approximately 10 % (9 % Chlorella meal supplementation), because the whole-body protein content and most physiological health parameters were highest under this condition, and the growth performance did not show a significant increase when the fish meal replacement rate exceeded 10 % (P > 0.05). These findings indicate the potential of Chlorella meal as a promising alternative to fish meal in feed formulations, offering benefits in enhancing growth performance and quality of marbled eel.