Elevated CO2 concentrations impacts growth and swimming metabolism in yellowtail kingfish, Seriola lalandi

Abstract

Elevated carbon dioxide concentrations [CO2] negatively impact the physiology, behaviour, and productivity of marine fish. CO2 impacts are commonly reported in response to ocean acidification but fish reared in recirculating aquaculture systems (RAS) are often exposed to [CO2] an order of magnitude higher. The yellowtail kingfish (Seriola lalandi), a high value marine species, is cultured in RAS in Europe and the southern hemisphere but the performance of this species to land-based RAS is not yet fully understood. The effects of elevated [CO2] on the mass-specific growth rate (SGRM) and feed conversion ratio (FCR) of juvenile S. lalandi (~230 g) was therefore assessed across a 54 day growth trial at 5 different [CO2]: 3.28 mg L−1 (ambient control), 12.52 mg L−1, 19.83 mg L−1, 28.2 mg L−1 and 39.6 mg L−1. The SGRM of S. lalandi showed a progressive reduction as [CO2] increased; a significant 13% decline in SGRM was first seen at 19.83 mg L−1 and was followed by a progressive stepwise decline in growth at higher [CO2]. FCR was statistically identical within the 3.28 to 28.2 mg L−1 groups but was significantly increased at 39.6 mg L−1. The clear threshold downturn in SGRM at 19.83 mg L−1 was hypothesised to be the result of a [CO2]–related metabolic burden that compromised aerobic metabolic scope (AMS) for growth. Subsequent swim flume respirometry therefore compared the mass-specific O2 consumption rate (MO2) of S. lalandi at 3.28 mg L−1 and 19.83 mg L−1 to establish SMR (Standard Metabolic Rate), maximum MO2 (MO2 max) and AMS for growth (AMS = MO2 max - SMR). As expected, impaired SGRM at 19.83 mg L−1 was associated with a lower AMS for growth resulting from no change in MO2 max but a significant rise in SMR. The results indicate that kingfish are a good candidate for intensive RAS because [CO2] is usually controlled to ≤15 mg L−1 and juvenile S. lalandi maintain growth and feed conversion across this range.