The levels of oxygen are one of the most important factors for a successful fish rearing, since it affects the feed intake, directly influencing growth. A concentration of at least 5 mg L-1 is the minimum required for a normoxia condition and less than 4 mg L-1 is considered hypoxia, provoking fish stress. The mechanisms involved in hypoxic stress have not yet been fully investigated on meagre (Argyrosomus regius), an interesting species for the diversification of Mediterranean aquaculture. The aim of this study was to investigate three levels of dissolved oxygen (moderate hypoxia, mild hypoxia and normoxia) on the performance of meagre.
The experiment was 31 days long and performed at the Aquaculture Research Station of the Portuguese Institute for Sea and Atmosphere (EPPO/IPMA). Fish initial body weight was 256.0 ± 1.8 g and density of 10.9 ± 0.1 kg.m-3 per tank. Three different levels oxygen were tested: moderate hypoxia (DO-1: 2-3 mg L-1), mild hypoxia (DO-2: 4-5 mg L-1) and normoxia (DO-3: 6-7 mg L-1) in triplicates. The 1.5 m3 tanks were in a flow through system with a renovation of 60% per hour, salinity kept at 37 and temperature at 20.7 ± 1.0°C. Pure oxygen was automatically added when the oxygen level was different from the treatment. Fish were fed with a commercial diet (SPAROS, Portugal) four times per day until apparent satiety. The uneaten pellets were counted and registered. For the final sampling, each fish was individually weighed and six fish per tank were anesthetized for blood collection (haematocrit (Hct), haemoglobin (Hgb), glucose (glu) and potassium (K+)) using an EPOC® card reader.
Average survival was 99.7 ± 0.7% for all treatments. Meagre from treatment DO-3 had a higher feed intake than DO-2, which also had a higher feed intake than DO-1. Final fish weight on DO-1 treatment was significant (p < 0.05) lighter than DO-2 and DO-3 and the same trend was found on Specific Growth Rate (SGR) showed at Table 1. In all blood parameters analyzed, no significant differences were found between treatments (p > 0.05).
Acknowledgments: This study was funded by project NOVIFEED - Novel tools for intelligent feeding management in Atlantic salmon and meagre farming (PT-INNOVATION-0099).