Length-Weight Relationships and External Morphology of Labeo rohita fed with Zinc Oxide Nanoparticles and Probiotics (Ecotec ®)

Background: The length-weight relationships (LWRs) are important parameters for assessing fish health and growth. Aims: This study aimed to investigate the effects of Zinc Oxide Nanoparticles (ZnO-NPs) and probiotics (Ecotec ®) on the LWR of Labeo rohita . Methodology: A total of 180 fish were distributed into six groups and were fed for 90 days with six experimental diets included: T0 (control), T1 (10 mg/kg ZnO-NPs), T2 (20 mg/kg ZnO-NPs), T3 (10 mg/kg ZnO-NPs + Probiotic 1g/kg), T4 (20 mg/kg ZnO-NPs + Probiotic 1g/kg), and T5 (Probiotic 1g/kg). Fish were fed with 3% of body weight. Results: T4 showed the highest values for all morphometric parameters, including mean wet weight (15.19 ± 1.94 g), total length (10.82 ± 0.34 cm), and other key measurements like fork length, head length, body depth, and body girth and also K value (1.20). Length-weight increments were highest in T4 (T4>T3>T5>T2>T1>T0). The log-transformed wet body weight showed significant positive correlations (P<0.001) with all morphometric parameters, except the condition factor, which was non-significant in T0, T1, and T3, but significant in T2, T4, and T5 (p<0.005). The slope (b) values indicated varying growth patterns: T0 (b = 2.809) and T1 (b = 2.853) exhibited negative allometric growth, T2 (b = 3.033), T3 (b = 3.070), and T5 (b = 2.905) displayed isometric growth, while T4 (b = 3.387) showed positive allometric growth. Conclusion: These findings highlight the potential of ZnO-NPs and probiotics, especially in combination (T4), to improve the LWRs in L. rohita .