Abstract
<jats:p>To investigate the aquatic environment and population characteristics affecting the growth of Planiliza abu (Heckel, 1843) in the middle sector of the Third River (Main Outfall Drain, MOD) in central Iraq, a comprehensive study was conducted from January to December 2022. The research assessed key water quality variables alongside the feeding ecology, age structure, and reproductive dynamics of this species. The results revealed that water temperatures exhibited profound seasonal fluctuations, ranging from a minimum of 9.15°C in January to a maximum of 37.54°C in August. Salinity concentrations followed a similar pattern, reaching their highest value in August (8.05) and dropping to the lowest level in April (2.58). The potential hydrogen ion exponent (pH) demonstrated a tendency toward alkaline conditions, with peak values recorded in August (8.6). Conversely, dissolved oxygen (DO) concentration reached its maximum during January, peaking at 9.875 mg/L, while never falling below the critical threshold of 4 mg/L throughout the study period. Nutrients also displayed distinct variations; nitrate (NO3) concentrations fluctuated between 0.66 mg/L in May and 1.12 mg/L in January, while reactive phosphate (PO4) concentrations mirrored this trend exactly, reaching their minimum in May (0.66 mg/L) after peaking in January (1.12 mg/L). Biological examination revealed an overall sex ratio skewed in favor of females, with 122 males versus 144 females (1 : 1.21). Feeding activity (%) showed clear annual fluctuations, peaking in summer at 87.93% and falling to 80.90 % in winter. Feeding intensity showed a similar pattern, with the lowest level recorded during the winter months (11.73 degree/fish) and the highest level during the summer months (14.11 degree/fish). Dietary analysis proved that P. abu exhibits a detritivorous, benthic-feeding behavior; diatoms occupied the foremost position regarding the Index of Relative Importance (%IRI), constituting 47.23 % of the dietary composition, succeeded by algae at 33.20 % and organic detritus at 11.19 %. In conclusion, the veterinary-sanitary analysis of water quality parameters revealed no exceedances of critical ecotoxicant toxicity thresholds, indicating the overall ecological well-being of the surveyed aquatory and the safety of the habitat for maintaining the optimal physiological status and sustainable reproduction of the P. abu population.</jats:p>