The success of fish farming heavily relies on maintaining optimal water quality in production systems. Among various water quality factors that impact fish productivity, waterborne high iron is a significant concern. In many regions of the United States, well water and underground water sources used for fish farming, often have high levels of iron, which can adversely affect fish health and growth. To achieve maximum growth and overall fish fitness, iron-induced toxicity must be alleviated.
Therefore, this research was undertaken to investigate the potential mitigation of iron toxicity by raising the pH of the fish culture water. Channel catfish (Ictalurus punctatus) was used as the test species as it is the leading aquaculture industry in the United States. To provide primary information on the sensitivity of catfish to iron toxicity under long-term realistic fish culture operation, a 10 day-LC50 test was conducted and calculated as 17.32 mg/L iron. For determining the protective effect of elevated pH levels on iron-induced toxicity, three levels of water pH, viz. 7.8 (control), 8.3, and 8.8 were tested against high iron (Fe, 4.33 mg/L representing 25% of 10-day LC50). Catfish were randomly divided into six groups in triplicate. The groups were (i) pH7.8(Control), (ii) pH8.3, (iii) pH8.8, (iv) pH7.8(Control)+Fe, (v) pH8.3+Fe, and (vi) pH8.8+Fe. Following the two-month trial, weight gain (%) reduced significantly in all Fe-exposed groups (irrespective of pH levels) compared to Fe-unexposed groups. However, relative to pH7.8(Control)+Fe, the Fe-exposed fish reared at a higher pH of 8.3 (pH8.3+Fe) exhibited enhanced ammonia excretion capacity (Fig. 1) and reduced toxic ammonia accumulation in plasma. Hemoglobin content and hematocrit were also highest in pH8.3+Fe compared to all other groups. In addition, exposure to Fe at control pH (pH7.8+Fe) incited hepatic oxidative stress based on an over-accumulation of malondialdehyde (MDA) along with a significant inhibition in superoxide dismutase (SOD) and catalase (CAT) activities; whereas in pH8.3+Fe and pH8.8+Fe, the MDA content restored to basal level accompanied by high CAT activity. Severe histopathological lesions were noted in gills at pH 7.8(Control)+Fe, which was also complemented by an over-accumulation of iron in the gills and plasma. In conclusion, although higher pH levels did not improve growth performance under iron exposure, raising the pH to 8.3 helped fish maintain ammonia homeostasis, blood health, anti-oxidant capacity, iron balance, and gill structure, suggesting a viable approach to managing iron toxicity in aquaculture systems.