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 confirm fish species identity. Based on multiple sequence alignment, larval sequences showed no ambiguities to the T. thynnus mitochondrial control region, thereby confirming spontaneous spawning in captivity. Although such an event has previously been reported in the Mediterranean, this is the first report supported by both morphological and genetic data.

Marine Aquaculture Impacts on Marine Biota in Oligotrophic Environments of the Mediterranean Sea – A Review

“…This form of aquaculture activity has a range of both positive and negative impacts on marine biota within the ecosystem. Grubišić et al (2013) reported spontaneous spawning of bluefin tuna (Thunnus thynnus) during rearing practices within cages, which could possibly increase the abundance of juvenile tunas in the open sea (Džoić et al, 2017), and have a positive effect on the resilience of this species to intensive fishery exploitation.…”

The genetic population structure ofThunnus thynnus(Linnaeus, 1758) in the Mediterranean Sea, a controversial issue

“…Sampling sites included the Strait of Messina which is an important foraging area for ABFT (Battaglia et al, 2013) and where tunas are present throughout the year, raising the hypothesis that a portion of the ABFT stock might be non-migratory (Genovese, 1956;Potoschi & Sturiale, 1996). Furthermore, mitochondrial sequences of ABFT from the Gulf of Mexico (Carlsson et al, 2007) and from the Adriatic Sea (Grubišić et al, 2013) were retrieved from GenBank and analysed with the sequences obtained in the present study. Interestingly, nucleotide sequences of ABFT from the Adriatic Sea had never been investigated before in a genetic population study including ABFT samples from other geographic areas.…”

“…AS) JX273444-JX273467(Grubišić et al, 2013) and YOY from the Gulf of Mexico (GM)(Carlsson et al, 2007) DQ 087556-DQ 087592.…”

“…On the other hand the Adriatic Sea has been interested by ABFT aquaculture during the past 10-15 years, ABFT specimens are captured primarily in the central Adriatic and transferred into rearing cages along the Croatian coast(Katavić et al, 2017). Spontaneous spawning by reared ABFT specimens, as reported in literature by more than one author(Džoić et al, 2017;Gordoa et al, 2009;Grubišić et al, 2013), could result in a genetic profile of offspring scarcely representative of wild panmictic population, introducing therefore a statistical bias in the population genetic analysis. Nevertheless, the Adriatic Sea sequences analysed in the present work were obtained by Grubišić et al (2013) from wild F I G U R E 2 (a) Plot of the Log posterior probability versus K for YOY; (b) ΔK calculated with Evanno's method F I G U R E 3 Bar plot of the posterior probability of the coefficient of membership for K = 2 using YOY.…”

“…Map of sampling locations of analysed Thunnus thynnus, sampling data are described inTable 1. AS: Adriatic Sea(Grubišić et al, 2013); SM: Strait of Messina; TY: Tyrrhenian Sea; IO: Ionian Sea; SS: Strait of Sicily TA B L E 1 Atlantic bluefin tuna (ABFT) samples examined for each area, grouped for age (YOY = young of the year; Juveniles; Adults) and essayed molecular markers (CR = mtDNA Dloop; STR = microsatellites) Software (Applied Biosystem). Each locus was tested for technical artefacts such as null alleles, large alleles dropout and stutter peaks, using the programme MICROCHECKER 2.2.1 (van Oosterhout, Hutchinson, Wills, & Shipley, 2004) (1,000 randomizations).…”