Relationship between fork and intestine length in Atlantic bluefin tuna (Thunnus thynnus).

Fish fork length data provide necessary information for catch statistics, fisheries biology and population studies. However, in bluefin tuna sampling, it is not always possible to collect fish measurements and researchers have to resort to biometric relationships. Through a linear function, we estimated bluefin tuna straight fork length (SFL) from intestine length and found a strong relationship between these variables (SFL =1.58 IntestineL -1.98, r= 0.96). This linear function can be used in future SFL estimations. Furthermore, the inverse of the slope of this equation represents the Nikolsky index (Ii), which provides information about feeding habits and classifies fishes as carnivore, omnivore or herbivore. We have obtained a Nikolsky index value of 0.64, which points to Atlantic bluefin tuna as a carnivorous fish. This observation is in agreement with previous studies.