Stereological assessment of the reproductive status of female Atlantic northern bluefin tuna during migration to Mediterranean spawning grounds through the Strait of Gibraltar

Abstract

The ovarian mass and gonadosomatic index (I G ) of bluefin tuna Thunnus thynnus, caught in the Strait of Gibraltar (Barbate) during migration to Mediterranean spawning grounds, were several times lower than those found in bluefin tuna from Mediterranean spawning grounds (Balearic Islands). Some of the bluefin tuna from Barbate (8·3%) were classified as immature (the most advanced oocytes present in the ovaries were early vitellogenic), and the majority (the remaining 91·6%) as non-spawning mature; the ovary contained late vitellogenic oocytes, but there was no sign of spawning activity. Stereological estimation indicated that the ovaries of spawning bluefin tuna from the Balearic Islands contained five-fold more highly yolked oocytes than bluefin tuna from Barbate. When breeding bluefin tuna cross the Strait of Gibraltar the gonad is at an incipient stage of maturation. The average batch fecundity estimated from stereological quantification of stage 4 (migratory-nucleus) oocytes in the specimens collected from Balearic was 92·8 oocytes g 1 of body mass, and the spawning frequency in this area was calculated to be 1·2 days. In specimens from Barbate a relative batch fecundity of 96·3 oocytes g 1 was estimated using stage 3 (late vitellogenic) oocyte counts. 2002 The Fisheries Society of the British Isles

On the Variability of the Length–Weight Relationship for Atlantic Bluefin Tuna,Thunnus thynnus(L.)

“…With the aim of ensuring that the samples selected from the traps belong to spawning ABFTs, we only selected fishes caught in April and May, which is confirmed by the studies of Rodríguez-Roda (1964, 1967 and Medina et al (2002). In the two cases (traps of Morocco and Spain) the mean value of the condition factor (K) of the selected samples was > 2, which, according to Rodríguez-Roda (1964) and Percin and Akyol (2009) The set of the three databases (N=673) will hereinafter be referred to as ALM+GBYP.…”

“…Con el fin de asegurarnos de que las muestras seleccionadas de las almadrabas pertenecen a ABFTs en fase reproductiva, hemos seleccionado sólo peces capturados en los meses de abril y mayo, algo que confirman los estudios de Rodríguez-Roda (1964, 1967 y Medina et al (2002). En los dos casos (almadrabas de Marruecos y de España) el valor medio del factor de condición (K) de las muestras seleccionadas es > 2, que según Rodríguez-Roda (1964) and Percin and Akyol (2009) El modelo EAST es la última adaptación hecha por los dos autores a los modelos publicados por Rodríguez-Marín et al (2013.…”

The paradox of the pelagics: why bluefin tuna can go hungry in a sea of plenty

“…This is in line with recent studies which identify benefits to growth and reproduction for species with foraging strategies that select a prey base with high energetic value and/or a broad size distribution , Sherwood et al 2002, Spitz et al 2012, Giacomini et al 2013, as opposed to one which relies entirely on abundance. Tunas, particularly bluefin, have elevated metabolic rates relative to other teleosts (Brill 1996), making them closer (in metabolic demand) to marine mammals and seabirds in that they require high rates of energy intake to satisfy their basal metabolic rates, large migratory (Block et al 2005, Wilson et al 2005, Galuardi et al 2010) and reproductive capacities (Medina et al 2002, Knapp et al 2014. Given these demands, it is not surprising that bluefin tuna consume a disproportionate amount of herring, which have high lipid content and energetic values relative to other abundant prey re sources on the Northwest Atlantic shelf (Lawson et al 1998).…”

“…During the summer foraging period, bluefin tuna build up large reserves of fat in their muscles and perigonadal mesenteric tissues. The quantity of fat determines migratory capacity (Chapman et al 2011) and reproductive output (Medina et al 2002, Knapp et al 2014, and is a primary factor that determines the market price of an individual fish (Bestor 2004). …”

Mechanisms of oocyte development in European sea bass (Dicentrarchus labrax L.): investigations via application of unilateral ovariectomy

“…Ovarian fragments were processed for plastic embedding and histological examination as described in García-Ló pez et al (2007), except that the tissue was fixed in 4% glutaraldehyde in PBS pH 7.4 at 4 8C for 24 h. To estimate the total number of oocytes at each developmental stage, the stereological method of Weibel (1979) as described in Medina et al (2002) and García-Ló pez et al Navas 2003). No significant differences in oocyte composition between the left and the right ovarian lobes were found in the fish of the INITIAL and SHAM groups (not shown) and thus the total oocyte number of the ULO-operated fish at 0 days was calculated by doubling the values obtained for the excised ovary.…”