Winter disease in gilthead seabream: Aquanéo's approaches for prevention and disease management

by Jean Peignon, Aquaculture Nutritionist, Aquanéo, France

Gilthead seabream: A mythical Mediterranean fish
Gilthead seabream (Sparus aurata) or ‘The golden javelin’ in Latin, is an emblematic fish from the Mediterranean Sea. Renowned for its delicate mild, white meat, gilthead seabream is present “in portion” on the plates of every Mediterranean seafood restaurant. Its consumption is very old in the area, as attested by the mosaics from Ancient Rome, showing detailed pictures of gilthead seabream or archaeological evidence of dried seabream trade 3,500 years ago from Bardawil lagoon in Egypt to the Middle East (Sisma-Ventura Guy et al, 2018.)
 

Traditionally, gilthead seabream was raised in extensive coastal lagoons, called “vallicoltura” in Italy or “hosha” in Egypt, in which the humans exploit their seasonal migrations from the sea into the lagoons by preventing any travel back to the sea. Thanks to its powerful jaws and teeth, the species is well adapted to extensive aquaculture as it is able to feed on various trophic niches, from soft prey like polychaetes or fishes to protected crustaceans or molluscs and even benthic plants (Chaoui et al. 2005).

In nature, young fish join the low water lagoons in spring, where the natural production and temperatures are high, and return in winter to the calm deep waters to reproduce. Nowadays, gilthead seabream is one of the two main species cultivated in Mediterranean, along with European seabass (Dicentrarchus labrax). In 2017 the aquaculture production in Mediterranean, based on sea cages, reached around 110,000 million tonnes (mt)

Cold temperatures: The gilthead seabream’s Achilles’ heel
Mediterranean farmers know it: compared to the European seabass, gilthead seabream is more sensitive to temperature drops. In nature, this sensitivity can be tackled by migratory behaviour. When temperatures drop, gilthead seabream leave their coastal areas to move to warmer and more stable deep waters, where they reproduce. Spawning occurs between December to January and juveniles join the coastal area to feed on more productive biotopes. Gilthead seabream is a protandrous hermaphrodite, meaning that they are functionally male in the first two years of their life before switching to females. Sex reversal occurs in around the second or third years and impacts the migratory behaviour: with age they tend to stay in deeper water.

Aquaculture in sea cages makes migration impossible and, therefore, gilthead seabream are facing challenging conditions during winter time as surface water parameters fluctuate with the weather conditions: temperature drop and unstable salinity generates a metabolic disruption characterised by an array of symptoms called the ‘winter disease’ or ‘winter syndrome’.

Read more, HERE.

The Aquaculturists

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