Immunocytochemical demonstration of close relationships between neuropeptidergic nerve-fibers and hormone-producing cell-types in the adenohypophysis of the sea bass (Dicentrarchus labrax)

Light microscopic double immunocytochemical stainings, performed on sea bass hypothalamo-hypophysial sections, revealed the projection of different neuropeptide-immunoreactive neurons innervating the hormone-producing cell populations in the pituitary gland. In the rostral pars distalis (PD) the ACTH cells were found in close proximity to fibers immunoreactive for somatostatin (SRIF), growth hormone-releasing hormone (GRF), corticotropin-releasing hormone (CRF), vasotocin (VT), isotocin (IT), substance P (SP), neurotensin, and galanin (GAL), while the PRL cell zone seemed only innervated by nerve fibers immunopositive for GAL. In the proximal PD, fibers immunoreactive for SRIF, GRF, VT, IT, cholecystokinin, SP, neuropeptide Y, and GAL formed a close relationship with the growth hormone cells. The gonadotrophs were observed near nerve fibers immunostained for gonadotropin-releasing hormone, IT, and less obviously GRF and VT, while fibers positive for GRF, CRF, VT, IT, SP, and GAL penetrated between and formed a close association with the thyrotrophs. In the pars intermedia the MSH cells and the PAS-positive (PAS+) cells seemed both innervated by separate nerve fibers immunoreactive for GRF, CRF, melanin concentrating hormone, VT, IT, and SP. All these results suggest a functional role of the neuropeptides in the adenohypophysis of the sea bass, possibly in the synthesis and/or release of hypophysial hormones from the different cell types.status: publishe

Ecological relevance and sensitivity depending on the exposure time for two biomarkers

Biomarkers are widely used to assess pesticide stress, but their ecological relevance and exposure time dependent sensitivity is still heavily debated. We studied both aspects in larvae of the damselfly Coenagrion puella, comparing the impact of low doses of atrazine, carbaryl, and enclosulfan on two key biomarkers (acetylcholinesterase [AChE] activity and fluctuating asymmetry [FA]) and their relationship with life history traits (mortality, development time, growth rate, and body size). Larvae exposed to the pesticides had, in general, longer development times. Size, growth rate, and mortality were not affected by any of the pesticides. In the long-term exposure, AChE activity was diminished by atrazine treatments and stimulated by carbaryl treatments, and was not affected in the enclosulfan treatments. FA decreased with increasing enclosulfan concentrations and showed no reaction to atrazine or carbaryl. Overall, short-term exposure tended to overestimate the results of long-term exposure decreasing growth rates and enhancing inhibition of AChE activity in atrazine and carbaryl treatments. In line with its ecological relevance, relationship between biomarkers and life history traits showed that AChE inhibition was positively correlated with mortality, while FA was traded off with size. These results show that caution should be exerted when using these biomarkers to assess pesticide pollution in field situations. (C) 2007 Wiley Periodicals, Inc.status: publishe

Gynogenesis in the African catfish Clarias gariepinus (Burchell, 1822) III. Induction of endomitosis and the presence of residual genetic variation

Gynogenesis is thought to be a useful method to generate fully inbred lines in teleost fish. Endomitosis, which refers to the inhibition of first mitosis, should lead to fully homozygous offspring. In this study, the optimal conditions to induce mitogynogenesis (endomitosis) by heat shocking of the eggs were determined in the African catfish Clarias gariepinus. Comparable survival rates were obtained with a shock of 40 degrees C applied for 1 min and a shock of 39 degrees C applied for 1.5-2 min. Applying the shock around 20 or 37 min after activation resulted in the highest survival rates (ca. 5% relative to the positive control). The amount of inbreeding (homozygosity) and paternal contamination were assayed by using polymorphic microsatellite DNA markers. In less than 1% of the offspring paternal alleles were present, indicating a true gynogenic background for most of the progeny. Meiogynogenetic and mitogynogenetic C. gariepinus showed a fair amount of residual heterozygosity (respectively 86% and 75% for one of the markers). Heterozygous catfish obtained through mitogynogenesis were attributed to the (simultaneous) presence of meiogynogens. In addition, we prove that the sex determining system of African catfish C, gariepinus is heterogametic in the male (XY/XX).status: publishe

Development of a lag time coating for drug-layered fish feed pellets

The purpose of this work was to develop a release-delaying coat for drug-layered fish pellets, in order to prevent a premature release of the drug in the tank water but allowing a rapid release after uptake by the fish. Blank pellets were prepared in a rotary processor and drug layered in a Wurster coater with bovine serum albumin or riboflavin using hydroxypropyl methyl cellulose (HPMC) as a binder. On the drug-loaded pellets, different mixtures of ethyl cellulose (EC) and HPMC were applied as the release-delaying coat. The aim was to obtain less than 10% drug release during the first 10 min followed by a fast release after the "lag" period, resulting in a sigmoidal release profile. In order to prevent coat bursts it was necessary to increase the amount of plasticizer from 20 to 40% triethylcitrate. To have a complete coat around the pellets, the thickness of the coat (amount EC) was important up to a certain level. The EC/HPMC ratio had a decisive influence on optimizing the permeability of the coating and realizing a sigmoidal release profile. The release rate was studied as a function of several formulation variables and physicochemical parameters (salinity, pH, and temperature) of the dissolution medium as the coating system is intended for different fish species. Salinity of the water proved to be important as well as the temperature. The developed system seems to be promising for a lot of ichthyologic applications, although it has to be evaluated for each intended drug, keeping in mind the properties of the particles to be coated, the fish species, and the environment.status: publishe

Analysis of the genetic structure of European eel (Anguilla anguilla) using microsatellite DNA and mtDNA markers

The spawning population of European eel (Anguilla anguilla L.) has been considered panmictic on the basis of genetic markers and morphometric studies. This hypothesis was tested by screening glass eel from five locations (Ireland, Italy, Morocco, Sweden and U.K.), belonging to two cohorts at the cytochrome b (cyt b) locus (392 bp) of the mitochondrion and at five nuclear microsatellite loci. Seventeen cyt b haplotypes were detected, of which ten were singletons; the most common haplotype occurred in 47% of all fish. Haplotype number increased significantly with latitude. Phylogeographical structure based on the cytoplasmic marker was weak (F-ST = 0.014) and non-significant. Close similarity was revealed between British and Irish glass eel populations, and weak differentiation among the British/lrish, Atlantic Moroccan, Italian and Swedish Baltic populations, respectively. No hierarchical genetic structure was obvious. Levels of genetic variation detected with five microsatellites were much higher levels than found with allozymes in previous studies (mean number of alleles per locus = 11.1; mean expected heterozygosity = 0.68). Overall among-population microsatellite variance was low but significant (F-ST = 0.004), and caused by the linked microsatellite loci Aan03 and Aan04. The Hardy-Weinberg-Castle equilibrium and the absence of gametic disequilibria at these loci in the Moroccan population might point to its genetic isolation, although the impact of just two out of five loci is puzzling. Given the weak differentiation typical for marine species and the limitations of our data, the results should be interpreted with caution. However, combined with recent evidence from a related study, the paradigm that the European eel constitutes a panmictic population becomes difficult to maintain.status: publishe

Mucosal response in African catfish after administration of Vibrio anguillarum O2 antigens via different routes

The aim of this study was to investigate the possibility of mucosal vaccination in African catfish (Clarias gariepinus) with Vibrio anguillarum O2 bacterins. The antigen was administered via different routes: anal intubation, oral administration, intraperitoneal injection and immersion. To monitor the antigen uptake, a competitive ELISA was used. The antibody response was measured using an indirect ELISA. Increased antibody levels were found in bile and mucus upon anal intubation, which was not the case after intraperitoneal injection. The data indicate that oral vaccination of fish may be possible when antigens can reach the second gut segment in sufficient quantities and in the right form as confirmed by the recorded substantial induction of systemic and mucosal immunity. The results obtained are a strong indication for mucosal immune response and the two compartmental models for immune response in fish.status: publishe