The success of fish farming heavily relies on maintaining optimal water quality. Among various water quality factors that impact fish productivity, waterborne high iron is a significant concern, which can adversely affect fish health and growth. To achieve maximum growth and overall fish fitness, iron-induced toxicity must be alleviated.
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 species in the United States. 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, exposure to high iron at neutral pH caused marked disturbances in plasma ion homeostasis. Concentrations of Na⁺, K⁺, Ca²⁺, and Mg²⁺ were significantly reduced, indicating compromised osmoregulatory capacity (Fig. 1). Elevating water pH to 8.3 and 8.8 ameliorated these disruptions, restoring plasma ion balance toward control levels. Gill ion transporter activity was strongly impaired by iron at pH 7.8, with significant suppression of Na⁺/K⁺-ATPase and H⁺-ATPase, indicating disrupted ion regulation. At higher pH, ATPase activities remained elevated, showing that alkalinity
mitigated iron’s inhibitory effects. Iron exposure also depleted energy reserves, lowering glycogen, protein, and lipid content in liver. Alkaline pH, especially 8.8, preserved energy substrates, reducing physiological costs under iron stress. Gene expression analyses showed that iron stress down-regulated the pathways related to ammonia excretion transport (Rhbg, Rhcg) and iron storage (Ferroportin, Ferritin), whereas elevated pH levels up-regulated/moderated these responses under iron exposure, suggesting improved ammonia and iron handling. In summary, this study shows that high iron disrupts ion balance, gill transport, energy metabolism, and gene regulation in channel catfish. Elevated pH restores homeostasis, preserves energy, and modulates stress responses.