Effects of Elevated CO2 on the Growth Performance, Respiratory Physiology, and Visual Acuity of Key Coastal Marine Fishes

Abstract

Elevated carbon dioxide (CO2) concentration in seawater has previously been demonstrated to have a range of negative impacts on marine fish. While ocean acidification is a well-known context in which elevated CO2 occurs, fish reared in recirculating aquaculture systems (RAS) may also be exposed to elevated CO2, and at concentrations which are even many times higher. The yellowtail kingfish (Seriola lalandi) and snapper (Chrysophrys auratus) are two marine fish species of high economic value in New Zealand which may be affected by elevated CO2 concentrations. To assess the effect of elevated CO2 on the growth, feed conversion, and respiratory physiology of yellowtail kingfish, juvenile kingfish (~230g) were reared in a 54 day growth-trial under the following CO2concentrations: (1) <5mgL-1(ambient-control), (2) 10-15mgL-1, (3) ~20mgL-1, (4) ~30mgL-1, (5) ~40mgL-1 Specific growth rates (SGRM) were greatest in ambient CO2 concentration (1), but this did not significantly differ from concentration (2). SGRM of kingfish were significantly lower by 13% at concentration (3) than (1). Surprisingly, feed conversion ratios (FCR) were nearly identical across the first three concentrations, which suggested that kingfish were able to utilise feed efficiently even in elevated CO2. Swim-flume respirometry was used to compare between metabolic rates of kingfish reared in ambient CO2(1) and elevatedCO2 (approximately concentration 3). Standard metabolic rate (SMR) was higher in kingfish reared in elevated CO2, contributing towards reduced aerobic metabolic scope (AMS). Therefore, decreased growth of kingfish at ~20 mgL-1 was mirrored by observations of reduced AMS. Overall, the findings experiments indicated that kingfish may be a good candidate species for farming in RAS conditions, due to productivity being robust at elevated CO2 concentrations typically expected in RAS. To assess potential climate change impacts (ocean acidification and warming) on visual acuity, snapper larvae were reared in two target CO2 concentrations (~400μatm and ~1000μatm) and temperatures (18°C and 22°C) in a 2 X 2 cross-design. Optomotor behavioural tests revealed that the visual acuity threshold of larvae across all experimental-conditions was 2°. Therefore, ocean CO2concentrations and temperatures projected to occur by the year 2100 may not significantly affect visual acuity in snapper larvae.