Abstract Although copper (Cu) is an essential trace element for fish, excessive concentrations can induce toxic effects. In contrast, nickel (Ni) is generally regarded as a non-essential heavy metal with potential toxicity. Collectively, exposure to concentrations exceeding safe thresholds for either metal poses a significant risk to fish health. Therefore, the combined toxicity of Cu–Ni co-exposure in Oreochromis niloticus was assessed with or without supplementation with watermelon rind (WMR). Fingerlings (37.30 ± 0.20 g) were randomly divided into four treatments: control, WMR (40 g/kg), Cu + Ni (3.35 and 3.60 mg/L, respectively), and WMR + Cu + Ni for 45 days. The findings demonstrated a significant decrease in growth parameters (weight gain and specific growth rate) and an increase in the feed conversion ratio and fish mortality due to Cu–Ni co-exposure. A decline in growth hormone levels and digestive enzyme activities (amylase, lipase, and trypsin) was accompanied by a rise in leptin levels in the Cu + Ni group. In addition, the histomorphology of intestinal tissues was altered, as evidenced by necrosis and epithelial desquamation, as well as reduced intestinal mucosal fold width and height. Additionally, decreased glutathione peroxidase, superoxide dismutase, and total antioxidant capacity, together with elevated malondialdehyde levels, were induced by Cu–Ni co-exposure. Furthermore, the combined exposure caused a downregulation of nutrient transporters (slc15a1a, slc15a2, and slc2a1b) and an upregulation of inflammatory genes (il1b and rela). Interestingly, the WMR diet enhanced antioxidant defences, improved digestive capacity, modulated gene expression, and ameliorated intestinal histology in the Cu + Ni-exposed group, resulting in increased growth and a reduction in mortality.
Abstract Sustainable poultry production increasingly relies on alternative protein sources; however, their effects on growth dynamics remain poorly understood because most studies evaluate body weight (BW) only at fixed ages. This study investigated whether cricket meal supplementation alters growth trajectories in Thai indigenous chickens using nonlinear growth-curve analysis. Betong and Nin Kaset chickens were reared under a 2 × 2 factorial arrangement and fed either a control diet or a diet containing 15% Acheta domesticus meal. Following quality-control procedures, individual BW trajectories from 108 birds were fitted using four nonlinear growth models (Brody, Gompertz, Richards, and Von Bertalanffy). Model performance was assessed using the coefficient of determination (R 2), adjusted R 2, Akaike information criterion, and Bayesian information criterion. The VB model provided the most consistent fit (mean R 2 ≈ 0.996) and was selected for subsequent analyses. Mixed-model analyses revealed no significant breed × feed × sex interactions. Cricket meal supplementation significantly reduced the asymptotic parameter ( A ; P = 0.0081) and integration constant ( B ; P = 0.0389), while increasing the estimated growth rate parameter ( k ; week−1; P = 0.0020). Across breeds and sexes, birds receiving cricket meal exhibited higher estimated k values and correspondingly steeper fitted growth trajectories, indicating differences in estimated temporal growth dynamics rather than a uniform increase in body size. These findings demonstrate that growth-curve analysis can reveal diet-induced changes in growth trajectories that may not be evident from BW measured at fixed ages and highlight its value for evaluating alternative feeding strategies in sustainable poultry production systems.
