Antonio Medina

Universidad de Cádiz | UCA · Department of Biology

ABSTRACT. Two distinct contingents of Atlantic bluefin tuna (ABFT), Thunnus thynnus (Linnaeus, 1758), occur in the Strait of Gibraltar (SoG): long-term residents and migrants. Long-term residents are commercially exploited all year round, while migrants are caught by traps on their migratory route towards Mediterranean spawning grounds. Although mi...

Foraging patterns and trophic interactions of young-of-the-year Atlantic bluefin (Thunnus thynnus, ABFT) and skipjack (Katsuwonus pelamis, SKJ) tunas co-occurring in coastal waters off the Gulf of Cadiz (GoC, East Atlantic Ocean) were investigated using stomach content and stable isotope analyses. Both species fed primarily on epipelagic fishes suc...

Chemical fingerprints in otoliths are commonly used as natural habitat markers in fishes. Alternatively, the first dorsal fin spine can provide valuable chemical information and may be more suitable for studying (i) endangered fish species that cannot be sacrificed for their otoliths or (ii) fishes for which otoliths might not be available because...

Two distinct contingents of Atlantic bluefin tuna (ABFT), migrants and residents, occur in the Strait of Gibraltar (SoG). Long-term residents are commercially exploited all year round using hook and line gears, whereas migrants are caught by traps in springtime as they pass through the SoG towards Mediterranean spawning grounds. While reproductive...

The Canary archipelago, which is part of the Atlantic biogeographical region of the Macaronesia, provides an appropriate habitat for tropical and temperate-water large pelagics. Atlantic bluefin tuna (ABFT, Thunnus thynnus) occur all year round in the Canary Islands. Life history traits of ABFT, specifically foraging patterns, have not been studied...

This study presents information about trophic relationships between juvenile albacore (ALB, Thunnus alalunga) and skipjack tuna (SKJ, Katsuwonus pelamis) in the Gulf of Cadiz (East Atlantic Ocean). Data on stomach contents (SCA) and stable isotope ratios of carbon and nitrogen (SIA) were analyzed to ascertain foraging patterns and trophic niche bre...

We examined late atretic follicles in ovaries of Atlantic bluefin tuna, Thunnus thynnus (Linnæus 1758), at different times of the year using transmitted light and epifluorescence microscopy. Atresia (degeneration and resorption of developing ovarian follicles) is a natural process involved in fecundity downregulation in teleosts, and is substantial...

The reproductive success of fish populations depends on their reproductive potential and offspring survival to maturity. The reproductive potential affects recruitment and hence populations’ resilience and productivity. Extensive research carried out throughout the current century has improved our understanding of the reproductive biology of the At...

We provide sound evidence of common dolphinfish (Coryphaena hippurus) spawning activity in the Gulf of Cadiz (SW Spain) during summer months. Along with waters off Ivory Coast, this area adjacent to the Mediterranean Sea is the easternmost Atlantic spawning ground documented for the species. All the fish analysed (5 males and 15 females) were at sp...

This report describes the 2020 ICCAT workshop on small tunas biology studies for growth and reproduction, hosted by the Instituto Español de Oceanografía, Málaga, Spain. The major objectives of the workshop were: 1) starting the creation of ageing and reproduction reference sets and, 2) providing more training for the ongoing sample collection and...

Foraging habits of skipjack tuna, SKJ (Katsuwonus pelamis), were investigated in three Spanish marine regions (Balearic Sea, Alboran Sea and Gulf of Cadiz) using stomach content (SCA), stable isotope (SIA), and fatty acid (FA) analyses. The three methodological approaches yielded significant differences among locations. All the studied areas appear...

The Strait of Gibraltar (SoG) houses a large diversity of marine species including large pelagic animals that use this area as permanent or temporary habitat. In particular, the SoG is home to a population of adult and sub-adult Atlantic bluefin tuna (Thunnus thynnus) that occurs there for most of the year. To gain further insight into the life his...

Atlantic bluefin tuna (ABFT) stocks have been considered overfished over the last decades, especially the western stock, whose main spawning grounds are in the Gulf of Mexico (GoM). Despite the current measures implemented, spawner bycatch by the longline fleet targeting yellowfin tuna (YFT) may explain the lack of recovery of local stock. This sit...

In this manuscript, we test how an understanding of geographical variation in larval fitness in relation to temperature and habitat use could be a useful method to improve our understanding of recruitment and develop better indices of annual recruitment. On the basis of the assumption that growth and survival of tuna larvae are influenced by temper...

The Alboran Sea holds one of the highest biological productivity rates in the Mediterranean, and thus represents an important nursing area for pelagic fishes including tunas. Trophic interactions between sympatric populations of age-0 bluefin tuna (ABFT) and Atlantic bonito (BON) were investigated in Alboran by integrating stomach content analysis...

Keywords: Thunnus Diet Feeding ecology Stomach content analysis (SCA) Bulk stable isotope analysis (BSIA) Amino acid stable isotope analysis (AA-CSIA) A B S T R A C T The trophic biology of age-0 Thunnus thynnus (ABFT) was investigated at two locations off the Iberian Mediterranean coast (Cambrils and Valencia) between 2012 and 2014 using stomach c...

Underwater PSAT tagging of bluefin tuna in purse-seine nets 2013

Underwater PSAT tagging of bluefin tuna in purse-seine nets 2009

Stable isotope analysis (δ13C and δ15N from liver and muscle) was used to assess trophic relationships between Atlantic bluefin tuna (ABFT) (Thunnus thynnus) and striped dolphin (SC) (Stenella coeruleoalbla) in the Strait of Gibraltar (SoG). δ15N values from ABFT muscle and liver tissues were significantly different from those of dolphin samples, b...

Life-history traits such as spawning migrations and timing of reproduction are adaptations to specific environmental constraints and seasonal cycles in many organisms' annual routines. In this study we analyse how offspring fitness constrains spawning phenology in a large migratory apex predator, the Atlantic bluefin tuna. The reproductive schedule...

The diet of Atlantic bluefin tuna (ABFT), Thunnus thynnus, caught in the Strait of Gibraltar area (SoG) from late summer through fall was assessed by stomach content (SCA) and stable isotope (SIA) analyses. Our results show that the SoG provides suitable food resources for sub-adult and adult ABFT. The SCA did not show inter-annual differences, and...

Mediterranean tuna farms account for > 60% of the eastern Atlantic bluefin tuna (ABFT) catch quota. Besides the direct impact of purse seining on wild stocks, ABFT farming practices may have environmental implications that are still poorly known. An unexplored potential source of interactions of ABFT farms with wildlife is the release of eggs into...

Knowing how migratory pelagic predators use food web resources during early life stages is essential for understanding population dynamics and recruitment. Feeding habits of ~3 to 4 mo old Atlantic bluefin tuna (ABFT) Thunnus thynnus from 2 Mediterranean nearshore areas (Cartagena and Cambrils, Spain) showing distinct oceanographic features were in...

El atún rojo del Atlántico (Atlantic Bluefin tuna, ABFT), Thunnus thynnus (Linnaeus, 1758), es un gran pez migratorio que habita en el Océano Atlántico Norte y el Mar Mediterráneo, y presenta adaptaciones fisiológicas y morfológicas que le permiten explotar una gran variedad de ecosistemas pelágicos. Desde la década de 1990 las poblaciones de ABFT...

The diet of young Atlantic bluefin tuna (Thunnus thynnus) in the Bay of Biscay foraging ground was assessed using stomach-content analysis (SCA) and stable-isotope analysis coupled with isotope mixing model. Whereas SCA showed that the young tuna fed mainly on horse mackerel (Trachurus trachurus), the estimation of liver and muscle mixing model ana...

The present chapter deals with the estimation of female fecundity in fishes, mostly teleosts. The chapter is organized in three main blocks. The first block is devoted to technical issues of fish fecundity measurements from fixation, preservation and treatment of ovarian material to automatic oocyte counts. The use of certain staining protocols for...

Despite attention focused on the population status and rebuilding trajectory of Atlantic bluefin tuna (Thunnus thynnus), the reproduction and spawning biology remains poorly understood, especially in the NW Atlantic. At present, the eastern and western spawning populations are believed to exhibit different reproductive characteristics and, conseque...

The present chapter deals with the estimation of female fecundity in fishes, mostly teleosts. The chapter is organized in three main blocks. The first block is devoted to technical issues of fish fecundity measurements from fixation, preservation and treatment of ovarian material to automatic oocyte counts. The use of certain staining protocols for...

Spawning behaviour of Atlantic bluefin tuna (Thunnus thynnus) was investigated using electronic satellite tags deployed in the western Mediterranean spawning ground, around the Balearic Islands (years 2009-2011). All the fish were tagged underwater and released within schools. In general, the fish tagged in the same year/school displayed common mig...

Ovarian tissue samples of Atlantic bluefin tuna (ABFT) spawners (n = 49) caught by purse seine in the Balearic Sea (western Mediterranean) were used to assess the stock reproductive characteristics. The frequency of spawning females estimated by the postovulatory follicle method was 84% and the spawning periodicity 1.2 days. Using an unbiased stere...

Stomach content analysis (SCA) and stable isotope analysis (SIA) coupled with isotopic mixing model analysis were used to estimate diet composition of pre-spawning Atlantic bluefin tuna (ABFT), Thunnus thynnus, caught by trap in the Strait of Gibraltar area. SCA provided poor information on diet as most of the stomachs appeared empty or contained o...

Lipid class, fatty acid and POP levels were measured in migrating Atlantic bluefin tuna (ABT) tissues caught off the Barbate coast, Spain. Tissue lipids were largely characterized by triacylglycerol, reflecting large energy reserves accumulated prior to reproductive migration. Fatty acid compositions of muscle, liver and adipose exhibited similar p...

Stable isotope analysis (SIA) has become a useful tool in trophic ecology research, but experimental studies are essential for their correct application in field studies. Young-of-the-year (YOY) Atlantic bluefin tuna (ABFT) caught in the Mediterranean Spanish coast were reared on a common natural prey to determine prey-muscle and prey-liver discrim...

A controlled-release implant loaded with GnRH agonist (GnRHa) was used to induce spawning in Atlantic bluefin tuna (Thunnus thynnus) during two consecutive reproductive seasons. The fish were implanted underwater and sampled between days 2 and 8 after treatment. At the time of GnRHa treatment, females were in full vitellogenesis and males in spermi...

The effect of a delivery system (implant) loaded with gonadotropin-releasing hormone agonist (GnRHa) on the spawning performance in captive-reared Atlantic bluefin tuna (Thunnus thynnus) was assessed by means of stereological quantification of ovarian post-ovulatory follicles (POF). Among untreated control fish no follicles were observed at the ooc...

The numbers of different types of ovarian follicles (developing, degenerating and postovulatory follicles) were estimated in bluefin tuna Thunnus thynnus using two stereological procedures: the model-based method of Weibel & Gomez, which has become a tool of broad application in the quantification of oocytes in fishes, and the assumption-free 'dise...

The effects of administration of gonadotropin-releasing hormone agonist (GnRHa) on proliferation and apoptosis of male germ cells were evaluated on Atlantic bluefin tuna (Thunnus thynnus L.) reared in captivity. Fish (n=19) were treated with a sustained-release delivery system loaded with GnRHa during the natural spawning season of 2004 and 2005 (J...

The presence, distribution, and histological features of lipofuscin granules were investigated in brains of the dendrobranchiate decapods Marsupenaeus japonicus Bate, 1888, Melicertus kerathurus (Forskål, 1775), Parapenaeus longirostris (Lucas, 1846) (family Penaeidae), and Aristeus antennatus (Risso, 1816) (family Aristeidae). Autofluorescent lipo...

The effects of gonadotropin-releasing hormone agonist (GnRHa) administration on testicular maturation and apoptosis of male germ cells of Atlantic bluefin tuna (Thunnus thynnus L.) reared in captivity were evaluated. Individuals classified at early and late spermatogenesis were equally present among untreated and GnRHa-treated fish. A lower rate of...

Atlantic bluefin tuna (BFT; Thunnus thynnus) is a migrating species straddling the North Atlantic Ocean and Mediterranean Sea. It is assumed that this species is divided into a western and an eastern stock, which spawn in the Gulf of Mexico and the Mediterranean Sea, respectively. To learn more about the reproductive behavior of the eastern BFT sto...

The effects of gonadotropin-releasing hormone agonist (GnRHa) administration on the gonads of 66 Atlantic bluefin tuna (Thunnus thynnus L.) reared in floating cages (La Azohía, Murcia, Spain) were evaluated using histological analyses. During two consecutive reproductive seasons (June–July 2004 and 2005), about half of the fish in each cage were ad...

Mature migrating Atlantic bluefin tuna (Thunnus thynnus thynnus) were captured in the Mediterranean Sea with a purse seine and reared in floating cages for 2 to 3 years. During the natural spawning period (June–July) of two consecutive years, fish were randomly implanted underwater with a controlled-release delivery system (implant) loaded with gon...

Comparative histological and stereological analysis of gonads from longline- and purse seine-caught Atlantic bluefin tuna Thunnus thynnus was undertaken to assess the reproductive potential of the population in the western Mediterranean breeding area. Bluefin tuna sampled by purse seine clearly had higher gonadosomatic index values (GSI) than those...

The spermatozoal ultrastructure in three solenocerid shrimps (Solenocera membranacea, S. africana, and Pleoticus muelleri) from different Atlantic locations was examined with the aim of increasing understanding of the phylogenetic relationships in the Dendrobranchiata. A considerable structural similarity between the sperm of these species and thos...

The acrosome-less spermatozoon of Aristaeopsis edwardsiana (Crustacea, Aristeidae), which consists of a central non-membrane bound nuclear region surrounded by a thin peripheral cytoplasm, much resembles that of the previously studied aristeid Aristaeomorpha foliacea. The marked spermatozoal similarities between these two species appear to indicate...

The Atlantic bluefin tuna (BFT; �Thunnus thynnus�) is a migrating species straddling the North Atlantic Ocean and Mediterranean Sea. The BFT population appears to be divided into a western and an eastern stock, which spawn, respectively, in the Gulf of Mexico and the Mediterranean Sea. To extend our understanding of the reproductive activity of the...

The Atlantic bluefin tuna (BFT; Thunnus thynnus) is a migrating species straddling the North Atlantic Ocean and Mediterranean Sea. It is assumed that BFT is divided into two populations: a western and an eastern stocks, which spawn, respectively, in the Gulf of Mexico (during April to June) and in the Mediterranean Sea (during June to August). To e...

The spermatozoal morphology of Loxopagurus loxochelis exhibits characters shared by other paguroids: complex concentrically zoned acrosome vesicle, capped by an electron-dense operculum and posteriorly penetrated by a large perforatorial chamber, and three microtubular arms emanating from the cytoplasm. The gen-eral sperm cell dimensions and arrang...

Ovarian ultrastructure of the Atlantic bluefin tuna (Thunnus thynnus) was investigated during the reproductive season with the aim of improving our understanding of the reproductive biology in this species. The bluefin, like the other tunas, has an asynchronous mode of ovarian development; therefore, all developmental stages of the oocyte can be fo...

The ovarian mass and gonadosomatic index (IG) 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...

The spermatozoa of Thunnus thynnus and Euthynnus alletteratus consist of an acrosome-less head (comprising the ovoid nucleus and the short midpiece) and a long flagellar tail that contains the conventional 9 + 2 axoneme and lacks lateral fins. The centrioles are arranged at approximately right angles and lie outside of a shallow nuclear groove. The...