Aquaculture of Atlantic Bluefin Tuna (Thunnus thynnus L. 1758): increasing morphological knowledge on larvae and juveniles

Introduction In the last decade, different European research Institutes and private operators have collaborated in order to close the biological cycle of Atlantic bluefin tuna (ABFT) in captivity. Since 2002, two National projects (MIPAF 6C82 and 6C138) allowed the creation of a ABFT broodstock in cage in Italy, in order i) to improve the knowledge on anatomy (Martini et al., 2007), reproductive biology (Caprioli et al., 2007a; 2007b), and stress response in captivity (Ferrante et al, 2003; 2007; 2008), ii) to develop a method for estimating numbers and weights of tuna in cages by means of image analysis (Costa et al., 2009), and iii) to train qualified personnel for tuna farming needs. In 2007, the regional research project ALLOTUNA was carried out in the same facility and the first ABFT induced spawning in captivity was recorded in 2008 (De Metrio et al., 2010) at first, and then in 2009 and 2010. The availability of ABFT viable and fertilized eggs from induced spawning in captivity moved the research efforts to the next step (larval rearing), and the enlargement of knowledge on ABFT larvae and juveniles, which represents an essential step in order to establish a reliable production of farmed BFT fingerlings. Material and Methods The sampled larvae and juveniles outcame from eggs obtained from hormonal induction of broodstock (De Metrio et al., 2010) maintained in a floating cage at the ABFT fattening facility Mare Nostro (Lat: 38°43'36.65" N; Lon: 16° 4'39.79" E, Calabria, Italy), during the spawning seasons 2008-2010. Eggs were split and larval rearing carried out in three different private Italian hatcheries: Panittica Pugliese (Apulia), Aquacoltura Lampedusa S.r.l (Sicily) and Civita Ittica S.r.l. (Latium). Some wild ABFT juveniles were also collected at maximum 4 miles far from the fattening facility. The following analyses were performed on 1-90 days post hatch (dph) larvae and juveniles from controlled spawning: 1) morphometric analysis, in order to describe the ontogenetic changes in shape and the pattern of morphological integration between body regions (head, trunk and tail) during growth; 2) histological observations on in toto 1-48 dph fish, in order to investigate on larval and juveniles ontogenesis; 3) scanning electronic microscopy (SEM) observations, in order to investigate on ontogenesis and equipment of sense organs; 4) observations on in toto stained individuals, in order to investigate on skeleton ontogenesis and anomalies. Each analysis was performed also on available wild samples. Results Some ontogenetic pattern in reared individuals vary accordingly with age (dph) (i.e., number of mucous cells in esophagus; gastric gland number in the stomach), other with size (teeth eruption; number and developmental stage of taste buds), other from individual to individual, independently from age or size (skeletogenesis). The shape trajectory evidences saturation plateau starting from 35-38 dph, where shape remains quite constant. In some lot, the 100% of reared larvae show abortive swim bladder and a very high frequency of individuals with skeletal deformities was observed. The main ontogenetic processes seem to be similar to those reported in literature on other tuna species.