Installation, operation and evaluation of a submerged cage at 45M depth in crete for the rearing of red porgy Pagrus pagrus

Abstract

Socio-economic factors related to management of costal zones and biological parameters related to species-specific requirements set limitations for the rearing location of net-pen sea cages. A cage was designed and installed at 45m depth based on the REFA Tension Length Cage technology at the cage facility of the Hellenic Centre for Marine Research in Crete. The cage-net module consisted of a net-pen contained within a hexagonal rigid frame to maintain the shape of the net. Vertical beams of the frame glider on six tension legs were placed in a circle. The operation of the cage was evaluated using a group of red porgy (Pagrus pagrus) for a rearing period of 4months whereas a second group reared in a surface net-pen cage served as control. Growth performance was similar between the experimental groups. The rearing method significantly affected fish skin pigmentation. Individuals reared in the submerged cage had a brighter skin colour and lower skin melatonin content compared with the ones reared in the surface cage. The presented submerged cage may provide a feasible alternative for rearing fish in exposed areas and particularly species requiring specific biological conditions, such as narrow temperature ranges and low light intensity.