Iron is an essential micronutrient for fish physiology, but it becomes toxic at elevated concentrations, posing a significant challenge in aquaculture systems where water quality management is critical. Excessive iron can induce oxidative stress, impair growth, compromise immune responses, and increase mortality in cultured fish, particularly in intensive indoor systems. Strategies that mitigate iron toxicity and enhance resilience are therefore of high interest for sustainable aquaculture.
This study investigated the role of mild iron pre-exposure in inducing stress memory in juvenile catfish (Ictalurus punctatus) to improve tolerance against subsequent lethal and sub-lethal iron stress. Juvenile catfish were pre-exposed to two sub-lethal iron concentrations corresponding to 5% (0.866 mg/L) and 10% (1.732 mg/L) of the 10-day LC50 for a period of 21 days, a parallel control (without iron pre-exposure “naïve”) was also considered. The experiment was conducted in triplicates (75 fish per 1000-L circular tank). Following pre-exposure, fish in all groups underwent a 7-day recovery in clean water to eliminate acute physiological stress effects before testing for stress memory. Recovered groups, along with parallel naïve controls, were subsequently subjected to either lethal (100% of 10-day LC50; 17.321 mg/L) or sub-lethal (25% of 10-day LC50; 4.330 mg/L) iron exposure for 21 days in 160-L glass aquaria (in triplicate). Results demonstrated that prior iron pre-exposure significantly enhanced tolerance to subsequent iron stress. Fish pre-exposed to the 10% LC50 dose exhibited the most pronounced protective effect, with improved survival rates and higher growth performance indicators (growth rate, SGR and FCR) compared to naïve and 5% LC50 pre-exposed groups. Under lethal iron exposure, the 10% pre-exposed group showed a 68% higher survival rate relative to controls (Fig. 1), while 5% LC50 pre-exposure induced moderate improvements, suggesting a dose-dependent effect of priming on stress memory formation. In conclusion, this study highlights that controlled pre-exposure to sub-lethal iron levels, particularly at 10% of the LC50, can enhance survival and growth in juvenile catfish under stressful iron conditions. This stress memory phenomenon may offer a promising strategy for improving resilience in aquaculture systems prone to iron accumulation, contributing to more sustainable and productive fish culture practices.