Replacing fish meal (FM) with chicken meal (CM)

Growth Performance

Partial Replacement (up to 50%): Studies consistently show that replacing up to 50% of FM with CM or PBM does not significantly impair growth in many juvenile fish species. For example, in juvenile rockfish (Sebastes schlegeli), replacing up to 20% FM with CM resulted in comparable weight gain and specific growth rate (SGR) to the control diet. Similarly, in Nile tilapia, up to 75% replacement with PBM showed no significant reduction in growth parameters like final weight, daily gain, or SGR.

Higher Replacement (75–100%): Complete or high-level replacement often negatively affects growth. In bullfrogs (used as a model for aquatic species), 100% FM replacement with CM led to reduced weight gain and lower amino acid content in muscle, likely due to nutritional imbalances. In large yellow croaker (Larimichthys crocea), growth and feed efficiency dropped significantly when PBM replaced more than 25% of FM, possibly due to reduced digestibility and palatability.

Species-Specific Responses: Some species, like Chinese soft-shelled turtles, showed improved growth at 10% PBM replacement, but higher levels (15%) had no adverse effects. In contrast, juvenile giant river prawns (Macrobrachium rosenbergii) maintained growth up to 75% PBM replacement.

Digestive Enzyme Activities

Partial Replacement: Moderate CM/PBM inclusion often enhances digestive enzyme activities. In bullfrogs, 50% CM replacement increased intestinal amylase and lipase activities, improving nutrient digestion and absorption. In Chinese soft-shelled turtles, 10% PBM replacement boosted trypsin, pepsin, lipase, and amylase activities, supporting better digestive capacity.

Complete Replacement: Full replacement tends to reduce enzyme efficiency. In bullfrogs, 100% CM replacement led to lower digestive enzyme activities and gene expression, correlating with poorer intestinal health and nutrient absorption. Similar trends were observed in large yellow croaker, where high PBM levels reduced the abundance of enzyme-producing gut bacteria.

Mechanism: Enhanced enzyme activity at lower replacement levels is linked to improved intestinal morphology (e.g., longer villi, thicker muscle layers), while high CM/PBM levels may cause amino acid deficiencies or anti-nutritional factors that impair digestion.

Energy Budget

Energy Utilization: Partial FM replacement with CM/PBM can improve energy utilization by reducing the feed conversion ratio (FCR). In bullfrogs, the 50% CM group showed a lower FCR, indicating better feed efficiency. In Nile tilapia, PBM diets maintained comparable FCR to FM diets up to 100% replacement, suggesting efficient energy use.

High Replacement Issues: At 100% replacement, energy budgets are often disrupted due to lower digestibility and nutrient imbalances. In bullfrogs, complete CM substitution increased malondialdehyde (MDA) levels, indicating oxidative stress and inefficient energy metabolism. In rockfish, higher CM levels (40–50%) reduced feed consumption, potentially limiting energy intake.

Digestible Energy: CM/PBM has high protein and energy content, but its amino acid profile may not fully match FM’s, affecting energy allocation for growth versus maintenance. Studies suggest supplementing essential amino acids (e.g., methionine, lysine) can mitigate these effects.

Additional Considerations

Antioxidant and Immune Effects: Partial CM/PBM replacement often enhances antioxidant enzyme activities (e.g., catalase, superoxide dismutase) and reduces inflammatory markers, as seen in bullfrogs and turtles. However, full replacement may increase oxidative stress and compromise immunity.

Sustainability and Cost: CM/PBM is cheaper and more sustainable than FM, making partial replacement attractive for aquaculture. However, complete replacement is generally unsuitable due to reduced performance.

Limitations: Most studies focus on specific species, and results may not generalize. Long-term effects and interactions with other dietary components (e.g., plant proteins) need further research.

Conclusion

Replacing up to 50% FM with CM or PBM in juvenile fish diets generally supports growth, enhances digestive enzyme activities, and maintains an efficient energy budget, with species-specific optimal levels (e.g., 20% for rockfish, 75% for tilapia). Higher replacements often lead to reduced growth, impaired digestion, and energy imbalances due to deficiencies in essential nutrients. For practical aquaculture, partial replacement with amino acid supplementation is recommended to balance performance and sustainability.

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