Miklós Bercsényi

Duplication of fgfr1 Permits Fgf Signaling to Serve as a Target for Selection during Domestication

The genetic basis of morphological variation both within and between species has been a lasting question in evolutionary biology and one of considerable recent debate. It is thought that changes in postembryonic development leading to variations in adult form often serve as a basis for selection . Thus, we investigated the genetic basis of the development of adult structures in the zebrafish via a forward genetic approach and asked whether the genes and mechanisms found could be predictive of changes in other species. Here we describe the spiegeldanio (spd) zebrafish mutation, which leads to reduced scale formation in the adult. The affected gene is fibroblast growth factor receptor 1 (fgfr1), which is known to have an essential embryonic function in vertebrate development. We find that the zebrafish has two paralogs encoding Fgfr1 and show that they function redundantly during embryogenesis. However, only one paralog is required for formation of scales during juvenile development. Furthermore, we identify loss-of-function alleles changing the coding sequence of Fgfr1a1 that have been independently selected twice during the domestication of the carp (Cyprinus carpio). These findings provide evidence for the role for gene duplication in providing the raw material for generation of morphological diversity.

The effect of initial stocking density on growth and survival of pike-perch fingerlings reared under intensive conditions

Pond-nursed pike-perch (Sander lucioperca) fry were trained to artificial diet and reared under controlled conditions maintained in aquaria using three stocking densities (1.25, 1.66 and 2.08 g/l). Two replicates per treatment were applied. The survival during the 4-week period of the experiment ranged from 44.2 to 49.6%. The majority of the losses were caused by cannibalism; only 8–14% could be attributed to natural mortality. Both cannibalism and natural mortality occurred in the first 2–3 weeks of rearing. The differences in the rate of cannibalism were independent of the stocking density. Natural mortality decreased with increasing density, consequently the highest survival was observed under the highest stocking density. Stocking density did not significantly influence growth, feed consumption and feed conversion ratio of the pike-perch fingerlings (p < 0.05).

Induced oogenesis of the European eel (Anguilla anguilla L.) in freshwater condition.

European eel is a catadromous fish species, which means that after living in freshwater premature individuals adapt to sea water, and migrate to the Sargasso Sea for spawning. Although male eel can be sexually matured even in freshwater, to date, it was believed that female eel can be matured only in seawater. Here we show that the process of sexual maturation may be induced in freshwater by treating female eels with carp pituitary (GSI = 9.87 ± 1.55%). It is thus proposed that seawater condition is not an obligatory environment for stimulating gametogenesis and for artificial maturation of the European eel in neither gender.

Disappearing scales in carps: Re-visiting Kirpichnikov's model on the genetics of scale pattern formation

The body of most fishes is fully covered by scales that typically form tight, partially overlapping rows. While some of the genes controlling the formation and growth of fish scales have been studied, very little is known about the genetic mechanisms regulating scale pattern formation. Although the existence of two genes with two pairs of alleles (S&s and N&n) regulating scale coverage in cyprinids has been predicted by Kirpichnikov and colleagues nearly eighty years ago, their identity was unknown until recently. In 2009, the ‘S’ gene was found to be a paralog of fibroblast growth factor receptor 1, fgfr1a1, while the second gene called ‘N’ has not yet been identified. We re-visited the original model of Kirpichnikov that proposed four major scale pattern types and observed a high degree of variation within the so-called scattered phenotype due to which this group was divided into two sub-types: classical mirror and irregular. We also analyzed the survival rates of offspring groups and found a distinct difference between Asian and European crosses. Whereas nude × nude crosses involving at least one parent of Asian origin or hybrid with Asian parent(s) showed the 25% early lethality predicted by Kirpichnikov (due to the lethality of the NN genotype), those with two Hungarian nude parents did not. We further extended Kirpichnikovs work by correlating changes in phenotype (scale-pattern) to the deformations of fins and losses of pharyngeal teeth. We observed phenotypic changes which were not restricted to nudes, as described by Kirpichnikov, but were also present in mirrors (and presumably in linears as well; not analyzed in detail here). We propose that the gradation of phenotypes observed within the scattered group is caused by a gradually decreasing level of signaling (a dose-dependent effect) probably due to a concerted action of multiple pathways involved in scale formation.

Flow cytometric detection of oxidative DNA damage in fish spermatozoa exposed to cadmium - Short communication

The aim of the present pilot study was to apply a flow cytometric assay, the so-called OxyDNA test, to determine the level of oxidative DNA damage in fish spermatozoa exposed to different concentrations (0.01-10,000 mg/L) of cadmium. Milt was collected from three randomly selected Prussian carp (Carassius auratus gibelio) males. Oxidative DNA damage was assessed with the OxyDNA kit and using flow cytometry. The ratio of OxyDNA-positive events increased significantly at higher cadmium concentrations. The results indicate that direct contact of fish spermatozoa with cadmium-polluted water initiates genotoxic damage.

The complete mitochondrial genome of perch Perca fluviatilis (Perciformes: Percidae).

Abstract In this study, we cloned and sequenced the complete mitochondrial genome of Perca fluviatilis. It was a circular double-stranded DNA molecule of 16,537 base pairs (bp) in length and consists of 13 protein-coding genes, 22 tRNA genes, two ribosomal RNA genes and two main non-coding regions (the control region and the origin of the light strand replication). The mitogenome of shared common features with those of other toleosts in terms of gene order and base composition. All protein-coding genes were initiated with ATG except for COX 1, which began with GTG instead. However, the termination codons of 13 protein-coding genes are varied with TAG, TAA or T. This mitogenome sequence data would contribute to better understanding phylogenetic relationships and population genetics of the family Percidae.

In vivo tracking of maturation in male European eel, Anguilla anguilla (L.), by computed tomography

The present study aimed in vivo tracking of maturation of male eel by computed tomography (CT). Additionally, individually monitored testes sizes were correlated with the conventionally used external maturity indicators (i.e. eye and nose indexes) in order to test and improve their usefulness at individual level. Testes could be clearly identified with the CT from the end of the third week of hCG administration routinely used to induce maturation in fish. The volume of testes increased exponentially during hormone treatment, and by the end of the sixth week of maturation procedure all males produced motilable spermatozoa. Present results prove that testes size can noninvasively be monitored with CT from maturity level where testes size rich 3000 mm3 volume. Eye and nose indexes are in close correlation with testes volume and thus can also be effectively used to monitor maturity level of male eel, but preferably only at stock level. However, due to their high individual variability, these indexes can be applied only with caution at individual level and should be supplemented with other noninvasive techniques such as CT.

Effects of high ambient temperature on fish sperm plasma membrane integrity and mitochondrial activity — A flow cytometric study

Local extreme climatic conditions occurring as a result of global climate change may interfere with the reproduction of animals. In the present study fish spermatozoa were incubated at different temperatures (20, 25, 30 and 40 °C) for 10 and 30 minutes, respectively and plasma membrane integrity and mitochondrial membrane potential changes were evaluated with flow cytometry using SYBR-14/PI and Mitotracker Deep Red FM fluorescent dyes. No significant differences were found in plasma membrane integrity at either incubation temperatures or time points. Mitotracker Deep Red FM histogram profiles indicating mitochondrial activity showed significant (p < 0.001) alterations in all cases of higher (25, 30 and 40 °C) temperature treatments as compared to the samples incubated at 20 °C. Our results indicate that fish spermatozoa exposed to high temperatures suffer sublethal damage that cannot be detected with conventional, vital staining techniques.

The complete mitochondrial genome of pike-perch, Sander lucioperca (Perciformes: Percidae)

Abstract The complete mitochondrial genome of Sander lucioperca has been sequenced and analyzed in this study. It was a circular double-stranded DNA molecule of 16,541 base pairs (bp) in length and exhibited 37 typical animal mitochondrial genes. The gene order and base composition were similar to those of other percid species. All protein-coding genes were initiated with ATG except for COX 1, which began with GTG instead. However, the termination codons of 13 protein-coding genes varied with TAG, TAA, TA or T. Within CR, we detected five copies of 10 bp tandemly repeated sequences domain, which immediately followed the tRNAPro. These mitogenome sequence data would contribute to better understanding phylogenetic relationships and population genetics of the family Percidae.