Adelino V. M. Canario

Thyroid hormones in growth and development of fish

The thyroid hormones (THs), thyroxine (T(4)) and triiodothyronine (T(3)) are products of the thyroid gland in all vertebrates. Their role in early development and metamorphosis is well established in mammals and amphibians, respectively, and recently several studies in fish have highlighted the importance of THs during flatfish metamorphosis. THs are present in high quantities in fish eggs and are presumably of maternal origin. During embryogenesis the concentration of T(4) and T(3) in the eggs decrease until endogenous production starts. Thyroid hormone receptors (TR) have been isolated from several teleosts and in common with tetrapods two receptor isoforms have been identified, TR alpha and TR beta. Both the receptors are expressed in early embryos and larvae of the Japanese flounder (Paralichthys olivaceus), zebrafish (Danio rerio) and seabream (Sparus aurata) although a different temporal pattern is apparent. The role of THs and TRs in fish embryogenesis, larval development and during metamorphosis will be discussed.

Weight-length relationships for selected fish species of the small-scale demersal fisheries of the south and south-west coast of Portugal

Abstract Weight-length relationships were estimated for 31 fish species from the south and south-west coasts of Portugal. These species, which are mainly sea breams (Sparidae), dominate the catches of the main fixed gears used in this region and account for more than 50% and 40% of the total fish landings by weight and by value.

Watching fights raises fish hormone levels.

Cichlid fish wrestling for dominance induce an androgen surge in male spectators.

Social modulation of sex steroid concentrations in the urine of male cichlid fish Oreochromis mossambicus.

The relationship between urinary concentrations (free + sulfates + glucuronides) of the steroids testosterone (T), 11-ketotestosterone (11KT), 17 alpha, 20 beta-dihydroxy-4-pregnen-3-one (17, 20 beta-P) and 17 alpha, 20 alpha-dihydroxy-4-pregnen-3-one (17, 20 alpha-P), and the social behavior of males of the cichlid fish Oreochromis mossambicus was investigated. After 8 days of isolation none of the steroids were good predictors of social dominance developed after subsequent formation of all-male groups. One day after group formation dominance indexes were good predictors of the urine concentrations of all sex steroids. Dominance indexes and androgen concentrations measured after all-male group formation were positively correlated with territoriality, courtship rate, and nest size. Similar relationships were found for progestins with the exception that they were not correlated with courtship rate. All-male group formation was also accompanied by an increase in urinary sex steroid concentrations in fish that became territorial and a decrease in non-territorial fish with the exception of T, which increased in both groups. Addition of ovulating females caused steroid concentrations to return to levels near isolation, except for 17, 20 alpha-P in territorials, which underwent a large increase. Thus, social interactions may have an important modulatory effect on sex steroid concentrations in O. mossambicus.

Why do winners keep winning? Androgen mediation of winner but not loser effects in cichlid fish

Animal conflicts are influenced by social experience such that a previous winning experience increases the probability of winning the next agonistic interaction, whereas a previous losing experience has the opposite effect. Since androgens respond to social interactions, increasing in winners and decreasing in losers, we hypothesized that socially induced transient changes in androgen levels could be a causal mediator of winner/loser effects. To test this hypothesis, we staged fights between dyads of size-matched males of the Mozambique tilapia (Oreochromis mossambicus). After the first contest, winners were treated with the anti-androgen cyproterone acetate and losers were supplemented with 11-ketotestosterone. Two hours after the end of the first fight, two contests were staged simultaneously between the winner of the first fight and a naive male and between the loser of first fight and another naive male. The majority (88%) of control winners also won the second interaction, whereas the majority of control losers (87%) lost their second fight, thus confirming the presence of winner/loser effects in this species. As predicted, the success of anti-androgen-treated winners in the second fight decreased significantly to chance levels (44%), but the success of androgenized losers (19%) did not show a significant increase. In summary, the treatment with anti-androgen blocks the winner effect, whereas androgen administration fails to reverse the loser effect, suggesting an involvement of androgens on the winner but not on the loser effect.

A test of the ‘challenge hypothesis’ in cichlid fish: simulated partner and territory intruder experiments

In male birds, the responsiveness of androgens to sexual and territorial behaviour is predicted to vary with mating system and the degree of paternal investment (‘challenge hypothesis’, CH; Wingfield et al. 1990, American Naturalist, 136, 829–846). The CH predicts a higher and longer lasting ‘breeding baseline’ androgen level in males of polygynous species with no or only short-term paternal investment than in males of monogamous species with a high degree of paternal investment. Since the applicability of the CH to nonavian vertebrates has been unclear, we experimentally tested its predictions in several cichlid fish (Neolamprologus pulcher, Lamprologus callipterus, Tropheus moorii, Pseudosimochromis curvifrons and Oreochromis mossambicus) using a simulated territorial intruder protocol. Androgens (11-ketotestosterone: 11-KT; testosterone: T) were measured from fish-holding water. In all species sampled, the 11-KT patterns confirmed the predictions of the CH originating from the avian literature, but T patterns did not. Males of all species sampled were highly responsive to territorial intrusions; however, the magnitude and duration of this response, that is, the rapid return to baseline 11-KT levels, could not clearly be explained by the degree of paternal care. 11-KT responses to interactions with ovulating females were observed in maternal mouthbrooders but not in biparental species (e.g. Lamprologini). At the interspecific level, androgen responsiveness was greater among males of monogamous species, as predicted, but also in species with more intense pair bonding (e.g. Tropheus moorii). Thus, this study confirms the predictions of the CH in cichlid fish at both the intraspecific and the interspecific levels.

European sea bass genome and its variation provide insights into adaptation to euryhalinity and speciation

The European sea bass (Dicentrarchus labrax) is a temperate-zone euryhaline teleost of prime importance for aquaculture and fisheries. This species is subdivided into two naturally hybridizing lineages, one inhabiting the north-eastern Atlantic Ocean and the other the Mediterranean and Black seas. Here we provide a high-quality chromosome-scale assembly of its genome that shows a high degree of synteny with the more highly derived teleosts. We find expansions of gene families specifically associated with ion and water regulation, highlighting adaptation to variation in salinity. We further generate a genome-wide variation map through RAD-sequencing of Atlantic and Mediterranean populations. We show that variation in local recombination rates strongly influences the genomic landscape of diversity within and differentiation between lineages. Comparing predictions of alternative demographic models to the joint allele-frequency spectrum indicates that genomic islands of differentiation between sea bass lineages were generated by varying rates of introgression across the genome following a period of geographical isolation.

Behavioural endocrinology: no hormonal response in tied fights.

Androgens are the principal sex steroids controlling reproduction and aggression in male fish, but their production can also be affected by social interactions. Here we show that androgen concentrations are not significantly increased in cichlid fish (Oreochromis mossambicus) that are fighting their own image in a mirror, despite their aggressive behaviour towards the virtual intruder. Our results indicate that the hormonal response normally triggered in male contests is not induced under these circumstances by the act of fighting itself, and that it may therefore depend on some indicator of relative fighting ability that cannot be delivered by a mirror-image challenger.

Non-invasive measurement of steroids in fish-holding water: important considerations when applying the procedure to behaviour studies

Fish behaviourists are increasingly turning to non-invasive measurement of steroid hormones in holding water, as opposed to blood plasma. When some of us met at a workshop in Faro, Portugal, in September, 2007, we realised that there were still many issues concerning the application of this procedure that needed resolution, including: Why do we measure release rates rather than just concentrations of steroids in the water? How does one interpret steroid release rates when dealing with fish of different sizes? What are the merits of measuring conjugated as well as free steroids in water? In the ‘static’ sampling procedure, where fish are placed in a separate container for a short period of time, does this affect steroid release—and, if so, how can it be minimised? After exposing a fish to a behavioural stimulus, when is the optimal time to sample? What is the minimum amount of validation when applying the procedure to a new species? The purpose of this review is to attempt to answer these questions and, in doing so, to emphasize that application of the non-invasive procedure requires more planning and validation than conventional plasma sampling. However, we consider that the rewards justify the extra effort.

Morphometric changes and sex steroid levels during the annual reproductive cycle of the Lusitanian toadfish, Halobatrachus didactylus

The Lusitanian toadfish has group synchronous oocytes, which grow from November until June-July when they are released probably as a single batch. Blood plasma levels of estradiol-17beta (E(2)) and testosterone (T) increase during vitellogenesis and drop rapidly during final maturation and ovulation, when 17,20beta, 21-trihydroxy-4-pregnen-3-one (17,20beta,21-P) levels increase. The male reproductive apparatus is composed of paired testes and multichambered accessory glands, which secrete mucosubstances and are connected to the spermatic duct. Changes in the gonadosomatic index of males paralleled the females but started to drop slightly earlier. The swimbladder and accessory glands also underwent important seasonal changes in weight reaching a maximum at spawning. T, 11-ketotestosterone (11-KT) and 17,20alpha-dihydroxy-4-pregnen-3-one (17,20alpha-P) were generally low except for a sharp peak in June. 17,20beta,21-P also peaked in June and then declined slowly. 17,20beta-dihydroxy-4-pregnen-3-one (17,20alpha-P) was undetectable in males and females. As with other species of the family two types of males were identified: type I males with smaller testes (ca. 7-fold) and larger accessory glands (ca. 3-fold) and swimbladders than type II. Type I males also had significantly higher (ca. 6-fold) 11-KT levels than type II males. This suggests a role for 11-KT in the development of structures important for reproductive behaviour.