Ivan Katavić

Temporal and spatial variability of pelagic wild fish assemblages around Atlantic bluefin tuna Thunnus thynnus farms in the eastern Adriatic Sea

The abundance and size structure of wild fishes aggregated around the sea-cages of two commercial Thunnus thynnus farms, including control locations, were assessed and compared over a 1 year period. The T. thynnus farms were located in the eastern Adriatic Sea, offshore of the islands of Ugljan and Brač. Fish assemblages were evaluated through visual census using scuba at 2 month intervals at two sites within each farm. The data suggest that wild fish assemblages at the study sites differed greatly; 20 species occurred at the Ugljan farm and 17 at the Brač farm, while only seven species were observed at the control locations. The abundance and diversity of wild fish assemblages were greater at the farms in comparison to control locations. The most abundant families were Sparidae and Belonidae (>80% of aggregated fishes). At both farms, the abundance and diversity of wild fishes were highest during summer, while diversity was lowest in winter and was mainly characterized by schools of bogue Boops boops and garfish Belone belone. Variability was also detected in spatial assemblages between farms; B. boops and B. belone were the most abundant species for the overall study at the Brač farm, while B. belone and saddled bream Oblada melanura were the most abundant at the Ugljan farm. The settlement also played a significant role in farm-associated fish assemblages, as both juveniles and advanced juveniles were common residents at farms. The majority of species which settled at the farms belonged to the sparids. Results indicate that aggregations of wild fishes at T. thynnus farms are persistent year-round, though the assemblage compositions and size structures of dominant species vary in respect to location and season.

Genetic characterization of wild and farmed European seabass in the Adriatic sea: assessment of farmed escapees using a Bayesian approach

&NA; Hybridizations between domesticated escaped farmed fish and wild conspecifics may increase genetic diversity or break down locally adapted gene complexes, thus reducing competitive ability and overall fitness. We examined the genetic structure of six farmed populations of European seabass, Dicentrarchus labrax, of different geographical origin, and ten neighbouring wild populations in the Adriatic Sea using 10 microsatellite loci. All loci were polymorphic, with mean expected heterozygosity >74% in all 16 populations. Overall number of alleles as well as short‐term effective population size were smaller in farmed (A = 18.7; Ne = 56.1) than in wild populations (A = 21.2; Ne = 180.6). The global FST of 0.0672 across loci showed significant population subdivision. Strong genetic differences between farmed fish and their wild conspecifics enabled the identification of seabass escapees back to their origins and the estimation of the extent of hybridization. Bayesian assignment analyses clustered wild populations together, whereas each farmed populations was assigned to a separate cluster. Intraspecific hybridization was highest in wild populations in areas impacted by fish farms, where highly admixed populations had decreased genetic diversity. The results of this study represent a solid foundation required to establish a genetic register of European seabass wild and farmed populations in the eastern Adriatic Sea that are required to establish a seabass DNA register.

Morphological and Genetic Identification of Spontaneously Spawned Larvae of Captive Bluefin Tuna in the Adriatic Sea

ABSTRACT The spawning behavior of captive Bluefin Tuna (Thunnus thynnus) was observed in cages at an Adriatic facility in summer 2011. Approximately 20,000 eggs were collected from cages and transferred to a land-based nursery, with an estimated fertilization success rate of 80%. Eggs were spherical with a diameter of 1,035.06 ± 20.16 μm and were pelagic with a single oil globule (227.63 ± 8.07 μm). Newly hatched larvae (3.08 ± 0.14 mm total length) followed scombrid larval development: melanophores were scattered over the body, head, notochord, and yolk, except finfold; eye pigmentation was observed 1.5 days posthatch, pectoral fins started to appear, and two-thirds of the yolk sac were absorbed; the mouth developed at 2.5 days posthatch, and larvae began feeding upon enriched rotifers. After mortalities occurred in the nursery (5 days posthatch), DNA was extracted from a sample of larvae. An 890 base pair fragment of the mitochondrial partial control region was amplified and sequenced to genetically con...

Embryonic and larval development of the tub gurnard Trigla lucerna (Pisces: Triglidae)

The embryonic and early larval development of the laboratory-reared tub gurnard, Trigla lucerna are described. The eggs ranged in diameter from 1.33 to 1.40 mm, with a mean of 1.36 ± 0.236 mm, were pelagic and spherical with a homogeneous and unsegmented yolk. There was single oil globule in the eggs. Globule ranged in diameter from 0.25 to 0.29 mm (mean 0.28 ±0.012 mm). Embryonic development lasted 115 h 2 min at mean temperature 13.5 °C. Newly-hatched larvae were 3.09 ±0.014 mm in total length. Absorption of the yolk sac was complete after the sixth day, when larvae reached 4.85±0.015 mm in total length. The only character for identifying eggs among species could be diameter, since the values obtained are lower than those obtained for Eutrigla gurnardus and Aspitrigla cuculus, but larger than those for Trigloporus lastoviza. The length of newly hatched yolk-sac larvae of tub gurnard is significantly lower (t-test, P<0.05) than those of most of the other gurnard species. Characters likely to help in identification of species will probably prove to be the length, shape and pigmentation of the pectoral fin, and the degrees of development of spiny armature on the head.