Tamás Müller

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).

Description of the song of the bush-cricket Saga rammei Kaltenbach, 1965 (Orthoptera: Tettigoniidae)

A detailed description of the spectrographic and oscillographic features of the male calling song of Saga rammei is presented for the first time. The study is based on Macedonian specimens. The song of S. rammei is a mainly amplitude-modulated signal having wide-band frequency spectrum containing well detectable frequency components between 15 kHz and 80 kHz (intensity maximum between 20–30 kHz). The male song is a sequence of echemes, which are composed of evenly and quickly repeated diplo-hemisyllabic syllables. Echemes begin with a gradually crescending initial part that leads to the main part of the echeme, where the peak amplitude of the syllables is nearly constant. This structure is similar to those described in other European Saga species (S. hellenica, S. campbelli, S. natoliae). However, the results suggest that amongst the European Saga species S. rammei produces the shortest echemes composed of the lowest number of syllables repeated with the highest syllable repetition rate and that the species sings with the shortest echeme repetition period. Those quantitative features make the song of S. rammei distinct and easily recognisable, and therefore could be used by females or males for species recognition.

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.

Intraovarian transplantation of stage I-II follicles results in viable zebrafish embryos

Maternal gene products drive early embryogenesis almost exclusively until the mid blastula transition (MBT) in many animal models including fish. However, the maternal contribution to embryogenesis does not stop at MBT, but continues to be an essential regulator of key developmental processes. The extent to which maternal effects contribute to embryonic and larval development is hard to estimate due to the technical difficulty of interfering with maternal gene products by conventional forward and reverse genetic tools. Therefore, novel methods to manipulate maternal factors in oocytes need to be developed. Here, we provide a proof of principle protocol for transplanting stage I-II zebrafish follicles into recipient mothers where donor stage I oocytes can develop to stage IV in 2 weeks and in 3 weeks they develop into mature eggs and produce viable offspring. Moreover, we show that simple microinjection of stage I-II follicles with RNA results in reporter gene expression in oocytes and paves the way for developing tools for interfering with maternal gene activity. This early stage oocyte transplantation protocol provides a means to study cellular and molecular aspects of oocyte development in the zebrafish.

Impact of environmental and genetic factors on the scale shape of zebrafish, Danio rerio (Hamilton 1822): A geometric morphometric study

Intraspecific morphological variability may reflect either genetic divergence among groups of individuals or response of individuals to environmental circumstances within the frame of phenotypic plasticity. Several studies were able to discriminate wild fish populations based on their scale shape. Here we examine whether the variations in the scale shape in fish populations could be related to genetic or environmental factors, or to both of them. In the first experiment, two inbred lines of zebrafish, Danio rerio (Hamilton 1822) reared under identical environmental conditions were compared. Secondly, to find out what effect environmental factors might have, offsprings were divided into two groups and reared on different diets for 12 weeks. Potential recovery of scales from an environmental effect was also assessed. Experimental groups could successfully be distinguished according to the shape of scales in both experiments, and the results showed that both genetic and environmental factors may notably influence scale shape. It was concluded that scale shape analysis might be used as an explanatory tool to detect potential variability of environmental influences impacting genetically homogeneous groups of fish. However, due to its sensitivity to environmental heterogeneity, the applicability of this technique in identifying intraspecific stock membership of fish could be limited.

Re-visiting phylogenetic and taxonomic relationships in the genus Saga (Insecta: Orthoptera).

Twelve of the 13 bushcricket species of the Saga genus are bisexuals and diploids, except the parthenogenetic and tetraploid bush cricket, Saga pedo. Despite a continuous research effort stretching through the 1900s, the taxonomic relationships of the Saga species are still disputed. In this study, our primary aim was to reveal natural relationships of the European Saga species and three of their Asian relatives, with special attention to the problematic taxonomy of two subspecies: S. campbelli campbelli and S. c. gracilis. Following a phylogenetic analysis of eight species, a comprehensive study was carried out on the above three taxa by using acoustic and morphometric approaches in parallel. Our phylogenetic data showed that European Saga species evolved from a monophyletic lineage. The geographical transitional species S. cappadocica was positioned between European and Asian lineages supporting the idea that the European Saga lineage originated phylogeographically from the Asian clade. The above results showed better agreement with the morphological data than with earlier ones based either on karyology or acoustic information only. After reviewing our data, we concluded that Saga pedo has most likely evolved from S. c. gracilis and not from S. rammei or S. ephippigera, as proposed by earlier studies. S. c. gracilis shares the same ITS2 haplotype with S. pedo, indicating that the latter could have evolved from populations of the former, probably through whole genome duplication. Based on acoustic and morphometric differences, we propose to elevate the two subspecies, S. campbelli campbelli and S. c. gracilis, to species level status, as Saga gracilis Kis 1962, and Saga campbelli Uvarov 1921. The present work sets the stage for future genetic and experimental investigations of Saginae and highlights the need for additional comprehensive analysis involving more Asian Saga species.

Habitat establishment, captive breeding and conservation translocation to save threatened populations of the Vulnerable European mudminnow Umbra krameri

In Europe 37% of freshwater fish are threatened. However, conservation activity is less widespread for fish compared to other vertebrate groups. The Vulnerable European mudminnow Umbra krameri is a marshland fish endemic to the Carpathian Basin. Its range and population have declined significantly since the 1990s. The main threats to the species are habitat loss and the invasive Chinese sleeper Perccottus glenii. During 2008–2012 a species conservation programme was established to rescue broodstocks from threatened populations, breed them under controlled conditions, translocate both rescued fish and their laboratory-reared offspring to surrogate habitats, and finally reintroduce offspring to their original habitats. Broodstocks from three threatened habitats were bred in the laboratory and produced offspring appropriate for stocking. Six artificial ponds were created in the pilot study area according to the environmental needs of the species, four of which proved to be suitable surrogate habitats in which translocated fish survived and reproduced successfully. Populations in the original habitats were supplemented with fish from laboratory breeding and from the natural recruitment of surrogate habitats, with special care of the corresponding broodstocks. Future challenges include improving our knowledge about the ecological processes in which the European mudminnow participates, identifying the most threatened populations, habitats suitable for restoration and potential areas for creation of surrogate habitats, and enhancing induced propagation methodology.

Ex situ protection of the european mudminnow (Umbra krameri walbaum, 1792): Spawning substrate preference for larvae rearing under controlled conditions

Captive breeding programs of endangered fish species, such as the European mudminnow Umbra krameri , are essential for population restoration. To improve captive spawning and larvae rearing under controlled conditions, two experiments were carried out. In the first, the spawning substrate preference was tested in triplicate, where five different types of artificial surface were provided for mudminnow pairs: (i) sand, (ii) artificial plants, (iii) gravel, (iv) sand + artificial plants and (v) gravel + artificial plants. All fish preferred the gravel + artificial plant combination, which indicates that this type of surface could be the most appropriate for spawning in captivity. In the second trial, three feeding protocols were tested in triplicate under controlled conditions. In the first treatment fish were fed exclusively with Artemia nauplii; in the second treatment fish were fed with Artemia for the first ten days then Artemia was gradually replaced with dry feed; for the third group the transition period started after 5 days of Artemia feeding. Although the survival rate of larvae could be maintained at a high level in some of the feeding protocols, a strong decrease in the growth rate was obvious in all diets containing dry food, which means that live food is essential for the first three weeks of mudminnow larvae rearing.

A note on the special fillet fatty acid composition of the dwarf carp (cyprinus carpio carpio) living in thermal Lake Hévíz, Hungary

Fatty acid (FA) composition of the fillet and the intestinal content of dwarf common carp (Cyprinus carpio carpio) living in Lake Hévíz was determined in wintertime collected samples and results were compared to widespread literature data on carp. Fillet FA profile of the thermally adapted (28 °C) Hévíz dwarf carps differed from profiles originated from divergent culture and feeding conditions in the overall level of saturation. Fillet myristic acid proportions largely exceeded all literature data in spite of poor dietary supply. Fillet fatty acid results indicate the effects of thermal adaptation (high saturation level) and the correlative effects of feed components rich in omega-3 fatty acids, with special respect to docosahexaenoic acid. With the application of discriminant factor analysis the Hévíz sample was accurately differentiated from the literature data on carp fillet fatty acid profile, mostly based on C14:0, C18:1 n9, C18:2 n6, C20:1 n9 and C20:4 n6 FAs. In summary, fillet FA profile suggested thermal adaptation, location specificity and the ingestion of algal and bacterial material.

Fusiform vateritic inclusions observed in European eel (Anguilla Anguilla L.) sagittae

Microscopic inclusions have been observed in 7 out of 106 European eel (Anguilla anguilla L.) sagittae using polarizing microscope and scanning electron microscope meanwhile the annual increments were studied to characterize the age structure of the population living in Lake Balaton. The presence of vaterite, a rare calcium carbonate polymorph was observed in these inclusions using Raman spectroscopy. Vateritic sagittae in wild fish are usually considered as symptom of physiological stress. The observed fusiform inclusions represent a new morphological type of vaterite inclusions in eel otolith. Two alternatives are hypothesized to explain their formation: 1) metabolic disorder, such as erroneous protein synthesis; 2) introduction of an alien protein into the eels inner ear. The origin and physiological significance of this new morphological type of vateritic inclusions is still an open question. Same as whether it can be found in other species or specific only to eel otoliths.