Changes in some morphometric relationships in Atlantic bluefin tuna (Thunnus thynnus thynnus Linnaeus, 1758) as a result of fattening process

The bluefin tuna business in Mediterranean coastal waters has increased substantially since the mid 1990s, following the demand from Asiatic markets. In addition, the fattening of captive bluefin tuna has developed greatly in a search for greater meat quality and better prices. The fattening process involves confinement, feeding ad libitum, and a suspected variation in some morphometric relationships. When the fork length (FL)-round weight (RW) relationship and condition index (K) of wild (n = 336) and fattened (n = 223) bluefin tuna (Thunnus thynnus thynnus Linnaeus, 1758) were compared, the fattened bluefin tuna became significantly heavier and their somatic condition also increased. These differences were not so clear below 180 cm FL. Small bluefin tuna do not seem to be as influenced by the fattening process as larger ones, since they are in a growth phase in which their metabolic rates may be a lot higher and would not permit them to become overweight. In a comparison of the equation used in fish biomass stereo-video estimation devices with the equation usually used to measure biometric relationships in fish, the alternative equation was more accurate for calculating the weight according to the size of fattened bluefin tuna.