Bibliothek

Notizen: Melatonin (MLT) was isolated from water samples using solid phase extraction cartridges and measured by radioimmunoassay. In tanks of rainbow trout Oncorhynchus mykiss, concentrations of MLT in water increased rapidly from 〈0·1 ng l−1 in the light phase to 0·7 ng l−1 in the dark giving calculated release rates of 〈1 ng kg−1 h−1 and 15 ng kg−1 h−1, respectively. This cycle in water MLT values corresponds to reported changes in plasma MLT concentrations. The colour of the tanks and a daytime acute handling stress did not affect concentrations of MLT in either the light or dark phase.

Notizen: Behavioural and electrophysiological responses of reproductive and non-reproductive female round gobies Neogobius melanostomus to water previously occupied by male round gobies (reproductive male water) were compared. Reproductive females spent more time than non-reproductive females in a tank near the input of water conditioned from reproductive males. Also, reproductive females swam significantly faster than non-reproductive females, suggesting that reproductive male odour may have activated spawning behaviour. Olfactory epithelial field potential measurement (electro-olfactogram, EOG) showed that reproductive male water was a potent olfactory stimulus to reproductive females, but not to non-reproductive females. Reproductive females responded significantly more than non-reproductive females to solid-phase (octadecylsilane) extracts of reproductive male water. Also, when these extracts were separated on reverse phase high performance liquid chromatography (HPLC), reproductive females showed noticeably greater responses than non-reproductive females to the fractions that eluted between 30 and 40 min. The behavioural data support the hypothesis that reproductive male round gobies release compounds into the water that attract potential mates. The EOG data indicate that these compounds can be quantitatively extracted from the water and be partially purified by HPLC. The evidence is not sufficient to indicate whether or not the compounds are steroids. The relatively early elution time on HPLC, however, suggests that if these compounds are steroids, then it is more likely that they will be conjugated rather than free steroids.

Notizen: In order to gain a better understanding of the reproductive cycles of male and female tench (Tinca tinca), gonadosomatic index, gonad histology and plasma concentrations of estradiol-17β (E2), testosterone, an drostenedione, 11-ketotestosterone (11-KT), 17,20β, 21-trihydroxy-4-pregnen-3-one (17,20β,21-P), 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P) and 17,20α-dihydroxy-4-pregnen-3-one (17,20α-P) were measured at the four seasons of the year, plus a further sampling coincident with the peak of spawning in early July. As expected, in both males and females, the plasma concentrations of androgens (excluding 11-KT in females – undetectable) and C21 steroids were significantly more elevated in the spring and summer (when most gonadal development took place) than in the autumn and winter. The only unexpected finding was that 17,20β-P and 17,20β,21-P, the steroids that are normally associated with oocyte final maturation in females and spermiation in males, were found in substantial amounts in both pre-vitellogenic, pre-spermatogenic and post-spawning fish. This suggests that these steroids may have other as yet unidentified roles in this species.

Notizen: The bile of sexually mature female rainbow trout Oncorhynchus mykiss has pheromonal activity which causes a significant increase in concentrations of 17,20β-dihydroxy-4-pregnen-3-one in the plasma of males. Bile from male trout is inactive. The activity in the female bile binds to octadecylsilane and can be eluted with methanol. The synthetic bile acids, taurocholic acid and taurolithocholic acid, are inactive.

Notizen: A procedure previously used for sex steroids was adapted to extract free cortisol and cortisone from water samples taken from rainbow trout Oncorhynchus mykiss tanks. Both corticosteroids could be readily detected by radioimmunoassay (RIA), with cortisol being predominant. All stages of the sampling, extraction and RIA procedure were validated for cortisol. An intermittent problem with poor replication was traced to the use of diethyl ether during the extraction procedure, and was overcome by the use of ethyl acetate. Other modifications were also introduced to speed up the procedure. The concentration and time course of release of both corticosteroids were shown to be related to the degree of stress that the fish had been subjected to. It was confirmed that cortisol concentrations in water and estimated cortisol release rates increased in response to handling stress, and that both were correlated with plasma cortisol concentrations. The potential for using water cortisol concentration and release rates to assess the primary stress response of fishes as a non-invasive alternative to blood sampling is discussed.

Notizen: Electro-olfactogram (EOG) recordings of the olfactory epithelium of both male and female roach Rutilus rutilus demonstrated that both sexes were able to detect free and glucuronidated 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P) with high sensitivity. Male, but not female, roach were also sensitive to androstenedione. Sexually mature female roach were shown to release free 17,20β-P, glucuronidated 17,20β-P and androstenedione into the water; for all three steroids, the rate of release was significantly enhanced by injection of carp pituitary extract (CPE). A series of trials was also carried out which showed that mature males, and to a lesser extent immature males and females, were able also to release free and glucuronidated 17,20β-P, both before and after CPE treatment. Water extracts from containers that had held CPE-treated mature male and female roach were examined for the presence of other steroids. This revealed that free and glucuronidated 17,20β-P plus free and glucuronidated 17,20β,21-trihydroxy-4-pregnen-3-one (17,20β, 21-P) predominated in water extracts from both sexes. The free moieties of 17,20α-dihydroxy-4-pregnen-3-one, 17-hydroxyprogesterone and 11-deoxycortisol were found at concentrations which were between four and 20 times lower than those of free 17,20β-P. Androstenedione was found at concentrations which were 25-fold lower than those of 17,20β-P. Despite its apparent high rate of release by sexually mature male and female roach, free 17,20β,21-P was found not to exhibit any EOG activity at the highest dose tested (10−7 M).

Notizen: There is increasing public, governmental and commercial interest in the welfare of intensively farmed fish and stocking density has been highlighted as an area of particular concern. Here we draw scientific attention and debate to this emerging research field by reviewing the evidence for effects of density on rainbow trout. Although no explicit reference to ‘welfare’ has been made, there are 43 studies which have examined the effects of density on production and physiological parameters of rainbow trout. Increasing stocking density does not appear to cause prolonged crowding stress in rainbow trout. However, commonly reported effects of increasing density are reductions in food conversion efficiency, nutritional condition and growth, and an increase in fin erosion. Such changes are indicative of a reduced welfare status—although the magnitude of the effects has tended to be dependent upon study-specific conditions. Systematic observations on large scale commercial farms are therefore required, rather than extrapolation of these mainly small-scale experimental findings. There is dispute as to the cause of the observed effects of increasing density, with water quality deterioration and/or an increase in aggressive behaviour being variously proposed. Both causes can theoretically generate the observed effects of increasing density, and the relative contribution of the two causes may depend upon the specific conditions. However, documentation of the relationship between density and the effects of aggressive behaviour at relevant commercial densities is lacking. Consequently only inferential evidence exists that aggressive behaviour generates the observed effects of increasing density, whereas there is direct experimental evidence that water quality degradation is responsible. Nevertheless, there are contradictory recommendations in the literature for key water quality parameters to ensure adequate welfare status. The potential for welfare to be detrimentally affected by non-aggressive behavioural interactions (abrasion, collision, obstruction) and low densities (due to excessive aggressive behaviour and a poor feeding response) have been largely overlooked. Legislation directly limiting stocking density is likely to be unworkable, and a more practical option might be to prescribe acceptable levels of water quality, health, nutritional condition and behavioural indicators.

Notizen: The plasma concentrations of testosterone (T) of cultured jundiáRhamdia quelen increased progressively during spermatogenesis and reached a peak at the beginning of spermiation (e.g. fluidization of the sperm and production of milt). Plasma peaks of T occurred simultaneously to the highest production of T by the testis, however, both plasma concentrations and testis production of T decreased progressively during spermiation. Concentrations of 11-ketotestosterone (11-KT) peaked c. 1 month after the peak of T, concomitant with enhanced production of 11-KT by the testis. The concentrations of 11-KT during the first cycle were extremely high (〉 1 μg ml−1), but less during the second and third cycles, suggesting that this steroid is most important during the pubertal phase in male jundiá. Plasma concentrations of both 17-hydroxy-4-pregene-3,20-dione (17-P) and 17,20β-dihydroxy-4-pregen-3-one (17,20β-P) were significantly higher during spermiation than at any other times, and showed little variation. The pattern of steroid changes was cyclical and consistent with their proposed roles in male fish reproduction.