Stress respiration and changes in CO2 concentrations affect the risk for H2S toxicity – Insights from model calculations

Sammendrag

Carbon dioxide (CO2), alkalinity, and pH are closely linked, but little information exists on how CO2 fluctuations influence hydrogen sulfide (H2S) toxicity in aquaculture systems. As fish respire, CO2 accumulates and lowers pH, which increases the proportion of total sulfide present as toxic H2S. During periods of elevated activity or stress, CO2 production rises further, potentially worsening this effect. We calculated how respiration driven CO2 increases can affect pH and the sulfide balance under typical post smolt RAS conditions (12 °C, 12 ppt, 25-200 mg/L alkalinity as CaCO3). Our results show that relying solely on inlet measurements can underestimate H2S risks. At high alkalinity and low CO2, only 5-10% of total sulfide appears as H2S at the inlet. If CO2 increases from 5 mg/L at the inlet to 15 mg/L in the tank, the resulting pH drop could increase H2S up to 2.4 fold. During stress, CO2 could reach 30 mg/L, leading to a further ~50% increase in H2S in the tank. Although higher alkalinity generally reduces overall H2S toxicity, it also makes systems more sensitive to rapid shifts in the sulfide equilibrium when CO2 rises. Our results clearly suggest that stress and its secondary effects on pH and chemical equilibria may be the missing link to explain the sudden onset and severity of H2S mortality events. Risk assessments for H2S must therefore consider the effects of alkalinity, stress and CO2 on sulfide balances within a system.

Les publikasjonen her:

DOI : doi.org/10.1016/j.aquaeng.2026...
NVA : hdl.handle.net/11250/5508726