Baseline respiration and spontaneous activity of sluggish marine tropical fish of the family scorpaenidae

Abstract

Baseline respiration and spontaneous activity were determined simultaneously for 6 specimens of tropical scorpionfishes, belonging to 2 different genera: Scorpaenopsis oxycephalus and S. diabolus (false stonefish) and Parascorpaena sp. and P. aurita. The experiments were conducted in an intermittent-flow respirometer at 24°C, at ambient light regime (12 h dark: 12 h light) and salinity (S=32). Permanent measurements of fish activity by an infrared video system (number of movements) and oxygen consumption were coupled allowing the calculation of a standard oxygen consumption (SOC) rate. The experimental set-up allowed quantification of spontaneous activity. Relative SOC values varied between 32.3 mg O2 h-1 kg-1 wet mass (wm) for a large S. oxycephalus (82 g WM) and 68.9 mg O2 h-1 kg-1 WM for the smallest investigated specimen, a P. aurita (16 g WM). The latter also showed the highest spontaneous activity rate (mean 98 movements h-l; max.: 870 h-l), while the values for the most sluggish individual did not exceed 24.6 h-1 (mean) and 480 h-1 (max.), respectively. Absolute SOC for a standard mass of 50 g was calculated to be 2.0 mg O2 h-1, using a wet mass versus oxygen consumption relationship of SOC (mg O2 h-1)=0.26×WM(g)0.527. The tropical scorpionfish investigated are some of the most sluggish fish found on coral reefs, with activity levels (means and variance) similar to that of boreal or polar scorpaenids (e.g. sculpins). In this respect, there was no indication for any specific adaptation to temperature. Baseline oxygen consumption values of the fish in this study were the lowest recorded for marine tropical species, and a first rough comparison of the resting metabolism of scorpaenid fish over a wide range of environmental temperatures might indicate a reduced thermal sensitivity of the tropical fish investigated.