As part of his study into the affect of cage size, Mr Samaras placed the same densities of seabass into three different sized polyethylene cages; small, medium and large, and monitored for eight months.
The initial number of fish per cage was 10 000, 1 770 and 55 individuals respectively and the cage sizes were as follows:
- 3 rectangular cages of 288 m3 (6 m x 6 m x 8 m) (large)
- 3 rectangular of 27 m3 (3 m x 3 m x 3 m) (medium)
- 3 cylindrical cages of 1 m3 (1 m diameter, 1.3 m depth) (small)
Specifically, Mr Samaras looked at the affect on growth, survival, and stress related parameters.
The results showed that there was a higher final body weight of the fish in the larger cages, followed by the medium size and then small.
Lower basel cortisol levels were also seen in the larger tanks and this result is notable as it is one of the lowest ever results observed with this species in literature.
Growth, food conversion ratio and survival rates were all also optimised in the larger cages.
Overall, the results showed an association of better performance with larger cage volumes.
The study has also showed that density might not be the critical factor but rather the available water volume for the expression of fish needs (swimming, schooling, social etc.).
Lower growth in the small and medium cages may also be due to the high cortisol levels which, in other species, have been shown to lead to reduced growth and feeding performance.
The trials took place in Souda Bay, Crete and were partly funded under the EU 7th Framework Programme by the AQUAEXCEL project.
October 2014
