Hybrid catfish production and water quality in split-pond systems at two fish-basin hydraulic retention times

Abstract Objective To compare production performance and water quality responses of hybrid catfish (female Channel Catfish Ictalurus punctatus × male Blue Catfish I. furcatus) in split-pond systems (SPS) operated at two fish-basin hydraulic retention times (HRT; 2 h versus 4 h) and to present a feed-based circulation coefficient (FCC) linking hourly circulation capacity to late-cycle daily feeding intensity. Methods A 6-month production trial was conducted in six 0.2-ha SPS ponds (20% fish basin, 80% treatment basin) circulated by slow-rotating paddlewheels. Three ponds were operated at a 2-h fish-basin HRT and three at a 4-h HRT. Hybrid catfish were stocked at 30,000 fish/ha and fed a 28% protein floating diet to apparent satiation once daily. Production outcomes were summarized as pond-level means with 95% bootstrap confidence intervals. Water quality responses were evaluated using linear mixed-effects models with HRT treatment, sampling date, and their interaction as fixed effects and individual ponds as a random intercept. Results Final biomass averaged 16,451 ± 2,081 kg/ha (2-h HRT) and 14,341 ± 3,824 kg/ha (4-h HRT), with confidence intervals overlapping widely across all production metrics. Mean influent–effluent differences for total ammonia nitrogen, nitrite-N, and total nitrogen remained near zero and showed no consistent treatment separation. The FCC values were 6.98 m3·h−1 per (kg·d−1) for the 2-h HRT treatment and 2.01 m3·h−1 per (kg·d−1) for the 4-h HRT treatment. Conclusion Comparable production and water quality outcomes across both HRT treatments indicate that the circulation rates tested were within an adequate operating range for the imposed biological loading. The principal limitation is the small number of replicate ponds, reflected in wide confidence intervals. The FCC provides a consistent practical metric for benchmarking circulation capacity relative to late-cycle feeding intensity in SPS design and operation.