Thyroid and pituitary gland development from hatching through metamorphosis of a teleost flatfish, the Atlantic halibut

Fish larval development, not least the spectacular process of flatfish metamorphosis, appears to be under complex endocrine control, many aspects of which are still not fully elucidated. In order to obtain data on the functional development of two major endocrine glands, the pituitary and the thyroid, during flatfish metamorphosis, histology, immunohistochemistry and in situ hybridization techniques were applied on larvae of the Atlantic halibut (Hippoglossus hippoglossus), a large, marine flatfish species, from hatching through metamorphosis. The material was obtained from a commercial hatchery. Larval age is defined as day-degrees (D =accumulated daily temperature from hatching). Sporadic thyroid follicles are first detected in larvae at 142 D (27 days post-hatch), prior to the completion of yolk sack absorption. Both the number and activity of the follicles increase markedly after yolk sack absorption and continue to do so during subsequent development. The larval triiodothyronine (T3) and thyroxine (T4) content increases, subsequent to yolk absorption, and coincides with the proliferation of thyroid follicles. A second increase of both T3 and T4 occurs around the start of metamorphosis and the T3 content further increases at the metamorphic climax. Overall, the T3 content is lower than T4. The pituitary gland can first be distinguished as a separate organ at the yolk sack stage. During subsequent development, the gland becomes more elongated and differentiates into neurohypophysis (NH), pars distalis (PD) and pars intermedia (PI). The first sporadic endocrine pituitary cells are observed at the yolk sack stage, somatotrophs (growth hormone producing cells) and somatolactotrophs (somatolactin producing cells) are first observed at 121 D (23 days post-hatch), and lactotrophs (prolactin producing cells) at 134 D (25 days post-hatch). Scarce thyrotrophs are evident after detection of the first thyroid follicles (142 D ), but coincident with a phase in which follicle number and activity increase (260 D ). The somatotrophs are clustered in the medium ventral region of the PD, lactotrophs in the anterior part of the PD and somatolactotrophs are scattered in the mid and posterior region of the pituitary. At around 600 D , coinciding with the start of metamorphosis, somatolactotrophs are restricted to the interdigitating tissue of the NH. During larval development, the pituitary endocrine cells become more numerous. The present data on thyroid development support the notion that thyroid hormones may play a significant role in Atlantic halibut metamorphosis. The time of appearance and the subsequent proliferation of pituitary somatotrophs, lactotrophs, somatolactotrophs and thyrotrophs indicate at which stages of larval development and metamorphosis these endocrine cells may start to play active regulatory roles.This work has been carried out within the projects ‘‘Endocrine Control as a Determinant of Larval Quality in Fish Aquaculture’’ (CT-96-1422) and ‘‘Arrested development: The Molecular and Endocrine Basis of Flatfish Metamorphosis’’ (Q5RS-2002-01192), with financial support from the Commission of the European Communities. However, it does not necessarily reflect the Commission’s views and in no way anticipates its future policy in this area. This project was further supported by the Swedish Council for Agricultural and Forestry Research and Pluriannual funding to CCMAR by the Portuguese Science and Technology Council

SPELMED : Evaluation of the population status and specific management alternatives for the small pelagic fish stocks in the Northwestern Mediterranean Sea : D. 2.2.1. Report on feeding ecology of small pelagic fish and their predators

SC NR. 02 - TENDER EASME/EMFF/2016/32 - SPELMED.-- 43 pages, 13 figures, 5 tables, 2 appendixesFeeding habits and trophic interactions are essential information in order to understand the functioning of marine food webs. Changes in the feeding habits or in prey quality or quantity may influence the body condition of the organisms and ultimately the growth and reproduction potential. Moreover, processes of competition with close related species can also influence the fitness of the species in a context of food limitation. We compiled and analyzed the published information on stomach content analyses, stable isotopes and indicators of ecosystem models for European sardine, European anchovy, round sardinella and European sprat. Moreover, published data on stomach content and stable isotope analysis of predators of SPF was also compiled and main predators of sardine and anchovy were identified. [...]Peer reviewe

Composition and structure of the larval fish community in the NW Iberian upwelling system during the winter mixing period

16 páginas, 11 figuras, 2 tablas.-- Open Access under Creative Commons by Attribution LicenceThe composition and structure of the larval fish community (LFC) in the NW Iberian upwelling system in late winter 2012 were examined, and the influence of abiotic and biotic factors on the horizontal distribution of fish larvae and on the horizontal structure of the LFC was investigated. The LFC, composed of 62 taxa (59 species and 3 genera) in 28 families, was dominated by Micromesistius poutassou followed by Scomber scombrus, Merluccius merluccius and Maurolicus muelleri. Multivariate analyses identified depth, sea surface temperature, geostrophic velocity and mesozooplankton biomass as the environmental factors involved in explaining variability in the LFC parameters (larval fish abundance, species richness and diversity) and revealed that the LFC was structured into coastal and slope larval fish assemblages. The main factor defining these assemblages was depth. However, the unusual coastal downwelling that occurred during the study would have participated in creating them and in maintaining assemblage boundaries, so that the importance of depth to the cross-shelf structuring of the LFC may have been overestimated. Our results suggest that larval fish assemblages in regions of coastal upwelling are driven by coastal downwelling during the winter mixing period and support the idea that fish larvae act as short-term (~10 d) biological tracers of the hydrography of the region during that periodThis work was funded by the Spanish research project CRAMER (CTM2010-21856-CO3-02) and by the Galician research project ECOPREGA (10MMA602021PR). The open access publication of this paper was funded by the Principado de Asturias research project GRUPIN14-144.Peer reviewe

GH/IGF Axis gene expression profile in developing atlantic bluefin tuna (Thunnus thynnus)

Resumen del trabajo presentado en el XIII Congreso de la Asociación Ibérica de Endocrinología Comparada - AIEC, celebrado online los días 16 y 17 de septiembre de 2021Atlantic bluefin tuna (ABFT), Thunnus thynnus (Linnaeus, 1758), is a large migratory oceanic top predator, considered as an important worldwide fishery source and a key species in pelagic ecosystems. Survival during the early life stages is crucial for future recruitment success, with larval growth being a determining process. Fish growth and development are mainly controlled by the GH/IGF axis, being involved in skeletal and soft tissue growth, as well as in immune function, appetite control, behavior (including foraging, aggression, and predator avoidance). To characterize the ontogenetic development profile of the GH/IGF axis at the level of gene expression, an ABFT larval rearing experiment (under controlled feeding conditions) was performed in the aquaculture facilities of the Spanish Institute of Oceanography (IEO), in Mazarrón during June 2019. Eggs and larvae from 3 replicates were collected regularly every 2-3 days from 0 until 30 days post-hatching (dph). In a total of 14 sampling points (n = 6-12 larvae) along the ontogeny, growth hormone (gh) and two forms of insulin growth factor (igf1 and igf2) were analyzed by real-time RT-PCR. A sigmoidal gh expression profile was observed, with higher values at 5 and 23 (maximum) dph, and lower values at 0 (minimum), 12 and 30 dph. Nevertheless, igf1 and igf2 showed a gradual increase from early days, also with lower values at 0 and 12 dph, but with maximum levels at 30 dph. Results are discussed considering growing rates and transition from larvae to juvenile, underlining the importance of gh/ igf axis during the ABFT early development and growthResearch funded by ECOLATUN CTM2015-68473-R (MINECO/FEDER). The authors wish to thank the technicians from the culture facilities of the Aquaculture Experimental plant in Mazarrón, Murcia (IEO-CSIC)

Dynamics of scale regeneration in seawater - and brackish water-acclimated sea bass, Dicentrarchus labrax

Scale loss is a common occurrence in both wild fish and those in aquaculture production systems, and regeneration of scales has been described in several freshwater species. Relatively little information exists about this process in marine fish, and in the present study, the chronology of scale regeneration was characterized in juvenile sea bass Dicentrarchus labrax, maintained in full seawater (SW; 36 %, 11.2 mM Ca2?) or brackish water (BW; 3.5 %, 1.1 mM Ca2?). Despite the significant differences in plasma osmolality, plasma calcium (Ca) and phosphorus (P) were similar between SW and BW.The authors thank Elisabete Caldas for technical assistance and Mr. Joa˜o Reis and Ms. Adriana Silva for care of animals. Fish provided by Viveiros Vilanova, S.A., V.N. Milfontes, Portugal. Funded by Fundac¸a˜o para a Cieˆncia e a Tecnologia, project No POCI/CVT/61052/2004 to DMP. PMG was in receipt of FCT grant SFRH/BPD/9464/2002

Involvement of growth hormone-insulin-like growth factor I

The role of growth hormone (GH) and insulinlike growth factor-I (IGF-I) in the tissue remodeling associated with the transition of a symmetrical larva to an asymmetrical juvenile during flatfish metamorphosis is unknown. In order to investigate the potential role of these hormones in the remodeling of cranial bone and soft tissue that accompanies eye migration during metamorphosis of Atlantic halibut (Hippoglossus hippoglossus) larvae, tissuespecific gene expression was monitored by in situ hybridization for Atlantic halibut type I growth hormone receptor (hhGHR), type II hhGHR, and insulin-like growth factor-I receptor (hhIGF-IR). Polyclonal antibody generated against the extracellular domain of type I hhGHR was used for the immunohistochemical localization of type I GHR protein. Type I hhGHR, type II hhGHR, and hhIGF-IR mRNA were expressed in fibroblasts, frontal bone osteocytes, and dorsal chondrocytes at the onset of metamorphosis (stage 8),during metamorphic climax (stage 9), and in fully metamorphosed juveniles (stage 10). Type I GHR protein showed similar expression patterns to those of type I hhGHR mRNA, except in chondrocytes in which little GHR protein was detected. The localization of GHR and IGF-IR transcripts and GHR protein in cranial structures that undergo remodeling is intriguing and suggests that, in addition to thyroid hormones, the GH-IGF-I system is involved in morphological transformations during metamorphosis in Atlantic halibut.We thank Heiddis Smáradóttir, Arnar Jónsson, and Øystein Saele for larval sampling, and Nádia Silva for methodological assistance