Stable isotopes and gut contents indicate differential resource use by coexisting asp (Leuciscus aspius) and pikeperch (Sander lucioperca)

Differential use of habitat and prey resources is an important mechanism that may allow coexistence of sympatric species. Unlike interactions between smaller cyprinid and percid fishes, the resource use by coexisting predatory asp (Leuciscus aspius) and pikeperch (Sander lucioperca) is relatively unknown. Here, gut content and stable isotope analyses were used to study ontogenetic dietary shifts and interspecific trophic niche overlap between asp and pikeperch coexisting in two reservoirs. The hypothesis that both species show an ontogenetic dietary shift from small invertebrates to large fish prey, but at the same time use different prey resources to reduce potential competitive interactions, was validated. The isotopic niches of the two predators showed no, or only a moderate, degree of overlap (0%–65%). The ontogenetic changes in the degree of interspecific isotopic niche overlap were different in the two reservoirs, suggesting that trophic segregation can be dynamic and variable among systems. Gut contents revealed that small (<100 mm standard length) asp consumed mostly terrestrial invertebrates and emerged aquatic insects, whereas small pikeperch foraged on zooplankton, larval and pupal stages of aquatic insects and fish. Larger individuals (>100 mm) of both species were predominantly piscivorous, with asp consuming more cyprinid prey and pikeperch more percid prey. Coexisting asp and pikeperch populations are able to utilise different prey resources, thereby reducing potential negative competitive interactions.     

Immunolocalisation of oestrogen receptors alpha (ERalpha) and beta (ERbeta) in porcine embryos and fetuses at different stages of gestation

The sites of oestrogen action can be shown by the localisation of their receptors in the target tissues. The aim of the present study was to show the localisation of oestrogen receptors in porcine embryos and fetuses obtained on days 18, 22, 32, 40, 50, 60, 71 and 90 post coitum (p.c.). The visualisation of proteins was conducted in embryos and various fetal organs such as gonads, uterus, lung, kidney, intestine and adrenal gland. Both ERs were observed in the blastocysts on day 18 p.c. In the male, ERbeta was detected in the testis and epididymis, whereas ERalpha was present in the efferent ductules. In the female, ERbeta was detected in the ovarian stromal cells investing the oocyte nests, while ERalpha protein was detected in the surface epithelium. In the uterus, ERs were present in the stromal cells, while ERbeta was present in the luminal epithelium. In the non-reproductive fetal porcine tissues ERbeta was localised in the lungs, kidneys, adrenal glands and in the umbilical cords. Both ERs were observed in the intestine. It is possible that ERbeta may play important roles in the development of the adrenal gland, testis, kidney and lungs, while both ERs are involved in the development of the ovary, uterus, epididymis and intestine of the porcine fetus.     

Circadian dynamics of locomotor activity and deltamethrin susceptibility in the pine weevil,Hylobius abietis

Rhythmic locomotor activity and daily susceptibility to deltamethrin were tested in the pine weevil,Hylobius abietis (L.) (Coleoptera, Curculionidae), a pest of young conifer plants. In constant darkness, beetles revealed a free-running circadian pattern of locomotor activity (average period 22h : 20min). Under long photoperiod, L:D 18:6, entrainment of motor activity was observed. In the entrained population of the weevils, a peak of locomotor activity occurred at about the beginning of the dark phase, and the minimum occurred in the middle of the light phase. Fluctuations of susceptibility to a standard dose of deltamethrin (0.5 μg/g body weight) varied across the day, and were inversely correlated to the changes in locomotor activity. The importance of considering the daily organization of insect biology in studying insect resistance to pesticides is re-emphasized. 3 www.csa.com. The following databases were screened: Animal Behaviour Abstracts, AGRICOLA, Aquatic Science and Fishery Abstracts, Biological Sciences, Ecology Abstracts, Entomology Abstracts, Environmental Science and Pollution Abstracts, Health and Safety Science Abstracts, Pollution Abstracts, Water Resource Abstracts, Toxicology Abstracts, TOXLINE.     

Sperm quality in male <Emphasis Type="Italic">Barbus barbus</Emphasis> L. fed different diets during the spawning season

Sperm quality of Barbus barbus L. was compared among the three following dietary regimes: Group A, fed 100% commercial diet (Karpico™ containing 33% crude protein and 6% fat), Group B, fed 78% commercial diet and 22% frozen chironomid (Chironomus plumosus) larvae, and Group C, fed 56% commercial diet and 44% frozen chironomid larvae. Concentrations of polyunsaturated fatty acids (PUFAs) in Group A, B, and C were 39.1, 42.0, and 44.6, respectively, as a percentage of total fatty acids. Sperm morphology, volume, concentration and motility, total number of spermatozoa, and osmolality of the seminal plasma were compared during the spawning season. Dietary regime did not influence sperm volume, concentration, or total number of spermatozoa, osmolality of seminal plasma, or the percentage of motile sperm, but significantly affected sperm morphology (except for anterior and posterior parts of the midpiece) and sperm velocity (P < 0.05). Groups B and C showed similar sperm characteristics during the spawning season compared to Group A. Almost all parameters changed either among or within groups during the spawning season, suggesting differences in terms of the optimal time for sperm collection. The best time for sperm collection was March for Group A, but April for Groups B and C, when the osmolality of the seminal plasma measured 289 mOsmol kg⁻¹ and sperm motility was maximal. Spermatogenesis, hydration, and cell decomposition were confirmed as the three major parameters controlling sperm characteristics during the spawning season. The possible correlation between sperm morphology and motility requires further study.     

Novel technique for definite blastomere inhibition and distribution of maternal RNA in sterlet Acipenser ruthenus embryo

Fisheries Science - The cleavage pattern of a vertebrate’s embryo is either holoblastic (complete) or meroblastic (partial). Sturgeon and other basal bony fishes represent a transition of the...     

Neuropeptides isotocin and arginine vasotocin in urophysis of three fish species

In this study, for the first time, both neuropeptides isotocin (IT) and arginine vasotocin (AVT) have been identified and measured in urophysis, the neurohaemal organ of the caudal neurosecretory system of teleost fish. So far, AVT, but not IT, was quantified by radioimmunoassay (RIA) in urophysis of several fish species. We have used high-performance liquid chromatographic assay with fluorescence detection (HPLC-FL) preceded by solid-phase extraction (SPE) and liquid chromatography-electrospray ionization triple-quadrupole tandem mass spectrometry (LC-ESI MS/MS) technique to determine both neuropeptides in urophysis of three fish species. The efficiency of peptide’s SPE extraction was 79–85 %. In HPLC-FL method, the limits of detection (LOD) and quantification (LOQ) were estimated as 1.0 and 3.4 pmol/mL for IT and 0.25 and 2.20 pmol/mL for AVT. In LC–MS/MS method, LOD and LOQ were estimated as 0.4 and 1.2 pmol/mL for IT and 0.06 and 0.2 pmol/mL for AVT. The chromatographic methods are good alternative for RIA, because enable to measure both nonapeptides simultaneously in one sample. In round goby (Neogobius melanostomus), three-spined stickleback (Gasterosteus aculeatus) and sea bream (Sparus aurata), urophysial IT concentrations ranged between 0.056 and 0.678 pmol/mg tissue and AVT concentrations ranged between 0.0008 (or even below detection threshold) and 0.084 pmol/mg tissue.     

The antioxidant system of sterlet seminal fluid in testes and Wolffian ducts

Oxidative stress is a possible source of spermatozoa function deterioration. Seminal fluid (SF) protects spermatozoa against reactive oxygen species (ROS) attack during development in testes and transit through the reproductive tract. Spermatozoa curvilinear velocity and percent of motile cells as well as changes in thiobarbituric acid-reactive substance (TBARS) content, superoxide dismutase, and catalase activity, and uric acid concentration in SF were evaluated in sterlet sperm collected from testes 24 h after hormone induction of spermiation and from Wolffian ducts at 12, 24, 36, and 60 h after hormone injection (HI). While testicular spermatozoa motility was not initiated in activating medium, Wolffian duct sperm showed low motility at 12 h, significant increase at 24 and 36 h, and decrease at 60 h. Testicular SF was characterized by the highest level of TBARS and activity of studied enzymes compared with SF from Wolffian duct sperm at 24 h post-HI. In fluid from Wolffian duct sperm, a significant increase in TBARS content was shown at 36–60 h post-HI. In contrast to testicular SF, in SF from Wolffian duct sperm, this increase was not counterbalanced by changes in the studied variables of antioxidant system. This may be the source of the observed decrease in spermatozoa motility parameters 60 h post-HI. The results may confirm a dual role of ROS in fish sperm physiology. The data with respect to decrease in sturgeon spermatozoa motility parameters at 60 h post-HI should be taken into account in artificial sturgeon propagation.