Fin spine bone resorption in atlantic bluefin tuna, Thunnus thynnus, and comparison between wild and captive-reared specimens.

Nicoletta Santamaria,Chrysovalentinos Pousis,Aldo Corriero,Fernando De La Gándara,Robert Vassallo-Agius,Giambattista Bello,Deepak Vashishth

doi:10.1371/journal.pone.0121924

Nicoletta Santamaria, Chrysovalentinos Pousis + Show 5 more

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https://doi.org/10.1371/journal.pone.0121924

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Abstract

Bone resorption in the first spine of the first dorsal fin of Atlantic bluefin tuna (ABFT) has long been considered for age estimation studies. In the present paper spine bone resorption was assessed in wild (aged 1 to 13 years) and captive-reared (aged 2 to 11 years) ABFT sampled from the Mediterranean Sea. Total surface (TS), solid surface (SS) and reabsorbed surface (RS) were measured in spine transverse sections in order to obtain proportions of SS and RS. The spine section surface was found to be isometrically correlated to the fish fork length by a power equation. The fraction of solid spine bone progressively decreased according to a logarithmic equation correlating SS/TS to both fish size and age. The values ranged from 57% in the smallest examined individuals to 37% in the largest specimens. This phenomenon was further enhanced in captive-reared ABFT where SS/TS was 22% in the largest measured specimen. The difference between the fraction of SS of wild and captive-reared ABFT was highly significant. In each year class from 1- to 7-year-old wild specimens, the fraction of spine reabsorbed surface was significantly higher in specimens collected from March to May than in those sampled during the rest of the year. In 4-year-old fish the normal SS increase during the summer did not occur, possibly coinciding with their first sexual maturity. According to the correlations between SS/TS and age, the rate of spine bone resorption was significantly higher, even almost double, in captive-reared specimens. This could be attributed to the wider context of systemic dysfunctions occurring in reared ABFT, and may be related to a number of factors, including nutritional deficiencies, alteration of endocrine profile, cortisol-induced stress, and loss of spine functions during locomotion in rearing conditions.

Highlights

The Atlantic bluefin tuna (ABFT), Thunnus thynnus (Linnaeus, 1758) (Osteichthyes: Scombridae), is one of the fastest, largest and long-lived teleost fish
This study aims to: 1) model the bone resorption progress in the first spine of the first dorsal fin of wild ABFT during growth; 2) describe seasonal differences in the bone resorption/deposition process and 3) compare the spine resorption process of wild and captive-reared Atlantic bluefin tuna
The integration of cross, frontal and sagittal sections indicates that the new bone material is deposed on the whole spine external surface as to progressively envelop it, so that the spine grows both in width and in length

Summary

Introduction

The Atlantic bluefin tuna (ABFT), Thunnus thynnus (Linnaeus, 1758) (Osteichthyes: Scombridae), is one of the fastest, largest and long-lived teleost fish. It can perform trans-Atlantic migrations and swim at 90 km per hour [1,2,3,4,5]. In the last 15 years, a capture-based aquaculture industry which concentrates on the capture of juvenile (tuna farming) or adult (tuna fattening) individuals and their rearing for a few years or a few months, respectively, before harvesting has developed in the Mediterranean Sea [11] Due to this industry, several European research institutions, in collaboration with the tuna farming and fattening industry, have participated in attempts to domesticate the ABFT since the early 2000’s [12,13,14,15,16,17,18,19,20,21,22,23,24]

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