## 4 Discussion  
To the best of our knowledge, this is the first study evaluating the effects of the inclusion of HFM in diets for _M. rosenbergii_. Unlike poultry by-product meal (PBM), which has been extensively studied in aquafeed, HFM remains poorly characterized, particularly in the nursery stage of freshwater crustaceans. The present study fills a critical gap by evaluating HFM in _M. rosenbergii_ post-larvae and contributes novel evidence that supports the dietary use of HFM as a viable protein source in aquafeed. Previous work demonstrated the feasibility of PBM as a substitute for fishmeal in prawn diets. In detail, up to 75% replacement of fishmeal with PBM did not adversely impact growth performance, survival rate, proximate body composition, or intestinal digestive enzyme activities of _M. rosenbergii_ juveniles [43]. These findings and the results observed in our trials align with previous research in various crustacean species, including _Penaeus vannanei_[44,45], _Cherax quadricirantatus_[46], and _Macrobrachium nipponense_[47], where PBM has been shown to effectively replace a substantial proportion of fishmeal without compromising prawn or shrimp growth and digestive functions. In contrast, the stable amino acid profile of prawns in the present study across all experimental groups suggests that the partial replacement of fishmeal with HFM preserved the amino acid profile of prawns fed with HFM. Regarding antioxidant status, consistent with our results, studies have reported no adverse effects on antioxidant defense mechanisms when incorporating poultry by-products in the diets of various aquatic species. For instance, [PERSON] et al. [48] found that the inclusion of poultry by-product meal in the diets of gibel carp (_Carassius auratus_ gibelio) did not negatively impact antioxidant status. [PERSON] et al. [49] observed no significant changes in antioxidant capacity and immune response in juvenile barramundi (_Lates calcarifer_) when fishmeal was entirely replaced with poultry by-product meal. The absence of significant differences in biomarkers of antioxidant status (MDA, GSH, GST, GPx, and GR) in the hepatopancreas of _M. rosenbergii_ post-larvae across the dietary treatments with increasing levels of HFM corroborates these findings. This suggests that the inclusion of HFM, up to a 6.0% inclusion level, is safe in terms of oxidative stress management. The hepatopancreas plays a crucial role in the antioxidant defense mechanisms in decapods by producing and secreting antioxidant enzymes [50,51]. Maintaining a balanced antioxidant status is essential for preventing oxidative damage to cellular components, ensuring overall health and optimal performance [52]. Notably, prawns fed diets containing 3.0% to 6.0% HFM showed improved performance and welfare. The improved final weight, antenna length, biomass gain, and feed conversion ratio with increasing HFM levels suggest increasing efficient utilization of nutrients in the diets, reflecting better overall health and welfare. Similarly, [PERSON] et al. [24] demonstrated that replacing fishmeal with HFM in diets for juvenile _Macrobrachium tenellum_ improved muscle fatty acid profiles without compromising growth, further supporting the use of HFM as a viable alternative protein source in prawn aquaculture. Likewise, [PERSON] et al. [12] reported that the inclusion of chicken protein hydrolysates in diets for _P. vannanei_ maintained the fatty acid profile of shrimps during nursery and grow-out phases. Comparable positive results have also been reported in fish. [PERSON] et al. [53] observed that the HFM dietary inclusion up to 12.5% maintains growth performance, nutrient utilization, and feed efficiency in European seabas (_Dicentrarchus labrax_). Unlike unprocessed feathers, HFM presents high crude protein content and digestibility [22]. Thus, HFM protein can more easily be absorbed and used for tissue maintenance. Although fishmeal is often considered the gold standard due to its balanced amino acid profile, HFM offers a competitive alternative.