Broodstock exposure to warming and elevated pCO2 impairs gamete quality and narrows the temperature window of fertilisation in Atlantic cod

Impacts of global warming and CO2-related ocean acidification (OA) on fish reproduction may include chronic effects on gametogenesis and gamete quality, as well as acute effects on external fertilisation. Here, temperature thresholds and OA-sensitivity of gametogenesis and fertilisation were investigated in Atlantic cod, Gadus morhua. Three broodstock groups of farmed cod (FC 1-3) were exposed for 3 months to three maturation conditions (FC 1: control, 6 degrees C/400 mu atm CO2; FC 2: warming, 9.5 degrees C/400 mu atm; FC 3: warming and OA, 9.5 degrees C/1100 mu atm). In addition, a broodstock group of wild cod (WC) was kept at control conditions to compare the acute temperature window of fertilisation with that of farmed cod (FC 1). Fertilisations were conducted in a temperature-gradient table at 10 temperatures (between -1.5 and 12 degrees C) and two CO2 levels (400/1100 mu atm). In FC 1 and WC, fertilisation success was relatively high between 0.5 degrees C and 11 degrees C (T-Range of c. 10.5 degrees C), indicating similar gamete quality in farmed and wild broodstocks kept at control conditions. Exposure of farmed broodstocks to warming (FC 2) and the combination of warming and OA (FC 3) impaired gamete quality, causing a reduction in fertilisation success of -20% (FC 2) and - 42% (FC 3) compared to FC 1. The acute temperature window of fertilisation narrowed from FC 1 (T-Range = 10.4 degrees C) to FC 2 (T-Range = 8.8 degrees C) and FC 3 (T-Range = 5.9 degrees C). Acute effects of CO2 on fertilisation success were not significant. This study demonstrates potential climate change impacts on gametogenesis and fertilisation in Atlantic cod, suggesting the loss of spawning habitat in the coming decades.

Automated summary

The impacts of global warming and ocean acidification on fish reproduction, specifically Atlantic cod, were investigated. The study found that both warming and the combination of warming and acidification resulted in reduced gamete quality and fertilization success in farmed cod. These findings suggest potential loss of spawning habitat in the future.