Relative Gonad Size Research Articles

Patterns of biogeographic and regional life-history trait variation in four large-bodied tropical wrasses

Ectotherms display substantial demographic variation across latitudinal gradients of temperature. Higher temperatures are often associated with smaller size, rapid initial growth rates, and early maturation, generally described as the Temperature-Size Rule (TSR). The longevity of most ectotherms also declines at warmer, lower latitudes. However, these patterns may be modified by increases in food resources that can flow on to continuous growth and large adult size. The present study estimates age-based demographic parameters of large-bodied tropical wrasses (Hemigymnus melapterus, H. fasciatus, Cheilinus fasciatus, and Oxycheilinus digramma) collected from Philippine fish markets (9–11°N) and sampled from Palm (18.53–18.70°S) and Whitsunday (20.05–20.21°S) reefs on the Great Barrier Reef, Australia (GBR). Differences in longevity, initial growth rates, and the age at sexual maturation at a biogeographic scale, between the Philippines and GBR, conformed to predictions of the TSR. However, Philippine specimens exhibited greater relative body condition and sustained periods of growth beyond sexual maturity resulting in larger adult size than GBR samples. Size-structure data from Philippine marine reserves and fished sites indicated that these differences were not confounded by fishery-dependent sampling. Moreover, latitudinal length–weight relationships could not be explained by lower densities of the focal wrasses in the Philippines or by relative gonad size. Less pronounced patterns of demographic variation that differed across species were evident at a regional scale, among Palm and Whitsunday reefs. Patterns of demographic variation between the Philippines and GBR strongly suggest that differences in food resource levels will be important in explaining the observed geographic variation.

Effects of laboratory salmon louse infection on mortality, growth, and sexual maturation in Atlantic salmon

Abstract Elevated salmon louse infection pressure generated by salmon farming represents a major threat for wild Atlantic salmon (Salmo salar). This study explored the effect of salmon lice on mortality, and body and gonad growth in F1 wild Atlantic salmon. Mature males (jacks) and immature fish were either infected with two different louse infection intensities (LIIs, 0.08 or 0.35 lice g−1) or kept as uninfected controls. Fish maturation was thereafter environmentally stimulated in seawater, followed by transfer to freshwater for 38 d to simulate river ascendance. No females matured, while 99% of the initially immature males started puberty. Jacks had high, and immature and maturing fish low, seawater mortality, independent of lice. The parasites had an LII-dependent negative effect on growth in length, weight, and condition factor in seawater. In freshwater, after the lice had detached, fish that were previously infected in seawater had reduced growth in length but not weight when compared to the uninfected control. The parasites did not affect relative gonad size in any fish phenotypes. The present results show that Atlantic salmon has a complex, and unexplored, regulation of growth when recovering from lice infection under laboratory settings. Further, the results suggest that possible negative effects of salmon louse on reproductive success in Atlantic salmon is most likely governed by the reduced body size and condition. However, further work on possible effects of salmon louse on semen quality is encouraged.

Spatial and environmental effects on Coho Salmon life history trait variation.

Adult size, egg size, fecundity, and mass of gonads are affected by trade‐offs between reproductive investment and environmental conditions shaping the evolution of life history traits among populations for widely distributed species. Coho salmon Oncorhynchus kisutch have a large geographic distribution, and different environmental conditions are experienced by populations throughout their range. We examined the effect of environmental variables on female size, egg size, fecundity, and reproductive investment of populations of Coho Salmon from across British Columbia using an information theoretic approach. Female size increased with latitude and decreased with migration distance from the ocean to spawning locations. Egg size was lowest for intermediate intragravel temperature during incubation, decreased with migration distance, but increased in rivers below lakes. Fecundity increased with latitude, warmer temperature during the spawning period, and river size, but decreased in rivers below lakes compared with rivers with tributary sources. Relative gonad size increased with latitude and decreased with migration distance. Latitude of spawning grounds, migratory distance, and temperatures experienced by a population, but also hydrologic features—river size and headwater source—are influential in shaping patterns of reproductive investment, particularly egg size. Although, relative gonad size varied with latitude and migration distance, how gonadal mass was partitioned gives insight into the trade‐off between egg size and fecundity. The lack of an effect of latitude on egg size suggests that local optima for egg size related to intragravel temperature may drive the variation in fecundity observed among years.

Reduced lactate dehydrogenase activity in the heart and suppressed sex hormone levels are associated with female-biased mortality during thermal stress in Pacific salmon.

Female-biased mortality has been repeatedly reported in Pacific salmon during their upriver migration in both field studies and laboratory holding experiments, especially in the presence of multiple environmental stressors, including thermal stress. Here, we used coho salmon (Oncorhynchus kisutch) to test whether females exposed to elevated water temperatures (18°C) (i) suppress circulating sex hormones (testosterone, 11-ketotestosterone and estradiol), owing to elevated cortisol levels, (ii) have higher activities of enzymes supporting anaerobic metabolism (e.g. lactate dehydrogenase, LDH), (iii) have lower activities of enzymes driving oxidative metabolism (e.g. citrate synthase, CS) in skeletal and cardiac muscle, and (iv) have more oxidative stress damage and reduced capacity for antioxidant defense [lower catalase (CAT) activity]. We found no evidence that a higher susceptibility to oxidative stress contributes to female-biased mortality at warm temperatures. We did, however, find that females had significantly lower cardiac LDH and that 18°C significantly reduced plasma levels of testosterone and estradiol, especially in females. We also found that relative gonad size was significantly lower in the 18°C treatment regardless of sex, whereas relative liver size was significantly lower in females held at 18°C. Further, relative spleen size was significantly elevated in the 18°C treatments across both sexes, with larger warm-induced increases in females. Our results suggest that males may better tolerate bouts of cardiac hypoxia at high temperature, and that thermal stress may also disrupt testosterone- and estradiol-mediated protein catabolism, and the immune response (larger spleens), in migratory female salmon.

Red operculum spots, body size, maturation and evidence for a satellite male phenotype in non‐native European populations of pumpkinseed Lepomis gibbosus

AbstractCarotenoid‐based pigmentation is a striking feature of many taxa, yet the function, if any, of colour traits is often unclear. Pumpkinseed Lepomis gibbosus, a widely introduced freshwater sunfish that exhibits alternative male mating strategies, express a striking, red operculum spot. To investigate the potential function of this red spot as a signal in this species' mating system, we determined the presence and measured the size of red operculum spots in fish collected from 12 populations in five European countries in which pumpkinseed is an established non‐native species. We subsequently related the presence and size of the red spot to body size and mating strategy, based on an analysis of relative gonad size (gonado‐somatic index, GSI), using a mixed modelling approach. The study demonstrated that the presence of a red operculum spot in pumpkinseed is associated with sexual maturation, with GSI frequency distributions suggesting that cuckolders in some non‐native populations comprised both sneaker and satellite males, the latter not having previously been reported for this species. Further, the size of red spot correlated strongly with body size in parental and cuckolder males, although there was no difference in the presence or size of the red operculum spot between male mating strategies. The function of a red operculum spot in females is not clear but may be partly mediated by pleiotropic genetic mechanisms. Red operculum spots appear to function as signals of male maturation and body size in pumpkinseed, irrespective of mating strategy.

Impact of rising temperature on reproductive investment in a capital breeder: The lesser sandeel

Capital breeding, whereby adult's build-up energy reserves at times when food is abundant in order to invest in reproduction during a time of low prey availability, is common in seasonal environments. A dependence on stored energy for reproductive investment may make capital breeders sensitive to rising temperatures during winter when activity and energy demands are typically low. The lesser sandeel, Ammodytes marinus (Raitt, 1934), is an extreme capital breeder, as gonad development is entirely dependent on stored energy whilst the fish remains buried in sand overwinter. In this laboratory study, the energetic consequences of high and low overwintering temperatures on energy allocation to reproduction in A. marinus were examined. The laboratory conditions led to growth and mass changes that were consistent with previously published field observations. Loss in wet mass was greater in the high temperature treatment, consistent with the higher metabolic cost predicted. Despite this, somatic energy loss did not differ between the two temperatures, the difference in mass being related to the lower relative gonad size in the high temperature treatment. The negative effect of temperature on reproductive investment in A. marinus highlights that although temperature can have a permissive effect on reproductive development it is limited by available energy reserves. Based on these findings it seems likely that warming will lead to a change in reproductive investment in A. marinus that mature but will not impact their overwinter survival.

A study of temporal effects of the model anti-androgen flutamide on components of the hypothalamic-pituitary-gonadal axis in adult fathead minnows

The aim of this study was to investigate temporal changes in the hypothalamic-pituitary-gonadal (HPG) axis of fathead minnows (Pimephales promelas) treated with the model androgen receptor (AR) antagonist flutamide. Reproductively-mature fish were exposed in a flow-through test to analytically-confirmed concentrations of either 50 or 500μg flutamide/L for 8 d, followed by an 8-d recovery period in clean water. Fish were sampled at 1, 2, 4 and 8days during each phase of the experiment. Flutamide (500μg/L) caused significant reductions in relative gonad size of the females on day 8 of the exposure and day 1 of the recovery, and reduced expression of secondary sex characteristics in males during the exposure phase of the experiment. Ex vivo gonadal synthesis of testosterone in both sexes (and 17β-estradiol in females) was reduced in the 500μg/L treatment within 2 d of exposure; however, steroid synthesis returned to levels comparable to controls by the end of the exposure portion of the test. Ex vivo testosterone synthesis in males exposed to 50μg flutamide/L was greater than in controls on days 4 and 8 of the exposure. Both the enhanced steroid production in the low treatment males, and return to control levels in the high treatment males and females during chemical exposure are indicative of a compensatory HPG response. One contributor to this response could be increased expression of genes responsible for enzymes involved in steroid synthesis; for example, transcripts for both cytochrome P450 side- chain cleavage and 11β-hydroxysteroid dehydrogenase were significantly elevated in flutamide-exposed males. Overall, responses of the HPG axis in adult male and female fathead minnows exposed to flutamide were both dynamic and comparatively rapid during exposure and recovery. These observations have ramifications both for the development of short-term fish assays to detect endocrine-active chemicals, and the derivation of robust adverse outcome pathways for AR antagonists in fish.

Physiological and condition-related traits in the gynogenetic-sexual Carassius auratus complex: different investments promoting the coexistence of two reproductive forms?

BackgroundCarassius auratus complex is an extraordinary species complex including the diploid and polyploid forms exhibiting asexual and sexual reproduction modes. The coexistence of both forms in the same habitats is currently reported. The stable coexistence of asexual and sexual forms assumes some disadvantages for asexuals that balance the costs of sex. In our study, we hypothesized and tested the differences in physiological (including heamatological and immunological), growth-related, condition-related, and fitness-related traits between gynogenetic females and sexuals.ResultsOur results revealed similar growth performance in gynogenetic females and sexuals measured by body size and weight, or expressed by condition factor. The energy allocation in reproduction measured by the relative size of gonads revealed no difference between gynogenetic and sexual females; in addition, both females in spawning expressed the same estradiol levels in blood plasma. We found a gender specific trade-off between investment in reproduction and immunocompetence (measured by the spleen-somatic index). Higher aerobic performance expressed by the heart index and higher oxygen-carrying capacity were found in sexual males, with increasing values before and during spawning. Our study evidenced significantly lower aerobic performance but higher oxygen-carrying capacity per erythrocyte in gynogenetic females when compared to sexuals. IgM production differed between gynogens and sexuals of C. auratus complex.ConclusionsOur study indicates that a similar amount of energy is invested by both gynogenetic and sexual females of C. auratus complex in reproductive behaviour. We suggest that lower aerobic performance in gynogens may represent their physiological disadvantage balancing the cost of sexual reproduction. A trade-off between the number of erythrocytes and the oxygen-carrying capacity per erythrocyte in sexual males and gynogenetic females may contribute to the coexistence of gynogenetic and sexual forms. In addition, the differences in specific immunity between gynogens and sexuals may also reduce the evolutionary disadvantage of sexual reproduction. In conclusion, we propose that several mechanisms contribute to the coexistence of the gynogenetic-sexual C. auratus complex.

Transcript variability and physiological correlates in the fathead minnow ovary: Implications for sample size, and experimental power.

Fundamental studies characterizing transcript variability in teleost tissues are needed if molecular endpoints are to be useful for regulatory ecotoxicology. The objectives of this study were to (1) measure transcript variability of steroidogenic enzymes and steroid receptors in the fathead minnow (FHM; Pimephales promelas) ovary to better determine normal variability and the sample sizes needed to detect specific effect sizes and to (2) determine how expression patterns related to higher level endpoints used in some regulatory ecotoxicology programs (e.g. relative gonad size). Estrogen receptor 2b (esr2b) and 5α-reductase a3 (srd5a3) showed high variability in the ovary (CV>1.0) while progesterone receptor (pgr), androgen receptor (ar), and esr2a showed comparatively low variability (CV=~0.5--0.7). Using these estimates, a power analysis revealed that sample sizes for real-time PCR experiments would need to be>20 to detect a 2-fold change for 7 of the transcripts examined; thus many molecular studies conducted in the fish ovary may have insufficient power to detect smaller effects. Two transcripts were correlated to steroid production in the ovary; cyp19a1 levels were positively correlated to in vitro E2 production, while ar levels were negatively correlated to in vitro T production. Thus, these transcripts may be informative molecular surrogates for ovarian steroid production. No transcript investigated showed any correlation to GSI, condition, or body weight/length. Molecular approaches in fish are increasingly used to assess biological impacts of chemical stressors; however additional studies are required that determine how molecular variability relates to higher level biological endpoints.

Reproductive strategies and seasonal changes in the somatic indices of seven small-bodied fishes in Atlantic Canada in relation to study design for environmental effects monitoring.

Small-bodied fishes are more commonly being used in environmental effects monitoring (EEM) studies. There is a lack of understanding of the biological characteristics of many small-bodied species, which hinders study designs for monitoring studies. For example, 72% of fish population surveys in Canada's EEM program for pulp and paper mills that used small-bodied fishes were conducted outside of the reproductive period of the species. This resulted in an inadequate assessment of the EEM program's primary effect endpoint (reproduction) for these studies. The present study examined seasonal changes in liver size, gonad size, and condition in seven freshwater and estuarine small-bodied fishes in Atlantic Canada. These data were used to examine differences in reproductive strategies and patterns of energy storage among species. Female gonadal recrudescence in all seven species began primarily in the 2-month period in the spring before spawning. Male gonadal development was concurrent with females in five species; however, gonadal recrudescence began in the fall in male three-spined stickleback (Gasterosteus aculeatus) and slimy sculpin (Cottus cognatus). The spawning period for each species was estimated from the decline in relative ovary size after its seasonal maximum value in spring. The duration of the spawning period reflected the reproductive strategy (single vs multiple spawning) of the species. Optimal sampling periods to assess reproductive impacts in each species were determined based on seasonal changes in ovary size and were identified to be during the prespawning period when gonads are developing and variability in relative gonad size is at a minimum.

Infection ecology of Philometra ovata (Nematoda: Philometridae) in a wild European minnow (Phoxinus phoxinus) population in Finland.

Seasonal life cycle of body cavity dwelling (BCD) Philometra ovata (Nematoda: Philometridae) has been reported in southern and central European countries, but its swim bladder dwelling (SBD) stage and northern populations have remained unstudied. In this study, we investigated the seasonal life cycle and infection ecology of P. ovata in both swim bladder and body cavity in the European minnow (Phoxinus phoxinus) in Finland. The larval P. ovata infected the swim bladder of minnows mainly in August. Female SBD P. ovata emigrated to body cavity mostly in September, grew to their full size by the end of the next June, and evacuated from minnows in July. In addition, female SBD P. ovata retarding their development and staying in swim bladder were found commonly in minnows, thus the mean monthly prevalence (6·7±3·9%) and mean intensity (1·4±0·8) of BCD P. ovata was lower than that of SBD P. ovata (37·8±15·1% and 2·0±1·5, respectively). Finally, despite the large size of BCD individuals, infection of P. ovata did not impair body condition and relative gonad size of minnows, but increased the mortality and caused physical damages in their hosts during the evacuation period.

Effects of Triclosan and Triclocarban, Two Ubiquitous Environmental Contaminants, on Anatomy, Physiology, and Behavior of the Fathead Minnow (Pimephales promelas)

Triclosan (TCS) and triclocarban (TCC) are two common antimicrobial agents found in many personal care products and subsequently are detected ubiquitously in wastewater effluent and receiving waters. Both compounds are of recent regulatory interest due to their omnipresence in the environment, including in humans. Although TCS and TCC have been suggested to be endocrine active, little information exists about their effects on organismal end points in development (growth, escape performance), anatomy (morphological indices, histology), physiology (vitellogenin), and behavior of exposed aquatic organisms. In this study, newly hatched fathead minnows were exposed for 12 days, and mature male and female fathead minnows (Pimephales promelas) were exposed for 21 days to environmentally realistic concentrations (nanograms per liter) of these two compounds singularly and in mixtures. At the end of the exposure, larvae were assessed for growth and predator-avoidance performance, and a subset of mature fish was assessed for plasma vitellogenin induction, expression of secondary sexual characteristics, relative size of liver and gonads, and histopathological changes to both organs. The remaining exposed mature fish were placed in breeding pairs of one male and one female minnow from the same treatment to assess their ability to defend a nest site and reproduce. Exposure to either antimicrobial compound, alone or as a mixture, caused no changes to larval fish, gonad size, or vitellogenin concentrations in mature fathead minnows. In contrast, decreased aggression was seen in adult male fathead minnows exposed to TCC (1.6 μg/l) or a mixture (560 ng/l TCS + 179 ng/l TCC and 1.6 μg/l TCS + 450 ng/l TCC). Decreased aggression would likely decrease their ability to defend and hold a nest site needed for spawning and reproduction. Substantial variability was found in the severity of observed effects within treatments, suggesting that environmentally realistic concentrations of these compounds may only affect particularly sensitive individuals.

Survival and iono-regulatory performance in Atlantic salmon smolts is not affected by atrazine exposure

This study was conducted to determine the potential effects of atrazine exposure on survival and physiological performance in Atlantic salmon ( Salmo salar) during the period of smoltification. This study involved two separate experiments in which juvenile Atlantic salmon were exposed to atrazine for a four day period in freshwater after which the fish were transferred to 50% seawater for two days and then to 100% seawater for five more days. The nominal concentrations of atrazine tested (1, 10 and 100 μg/L) were representative of and exceeded the levels measured in the North American freshwater environment. After seven days in seawater, fish were weighed, bled for the determination of plasma electrolyte levels, euthanized and samples collected for the determination of gonadosomatic index, muscle water content and gill Na+/K + -ATPase activity. Measured atrazine concentrations during the freshwater exposure period were 76–99% of nominal levels. There were no mortalities attributed to atrazine exposure. There were also no statistically significant differences in body weight, plasma sodium, potassium, magnesium and chloride levels, muscle water content or gill Na+/K + -ATPase activity between control and atrazine treated fish. Measurement of testis and ovary weights showed that there were no treatment effects on relative gonad size in male or female fish. These studies have shown that short term exposure to atrazine during the freshwater phase of their lifecycle had no effects on subsequent survival, body weight, relative gonad size or various measures of iono-regulatory performance in juvenile Atlantic salmon upon transfer to seawater. The concentrations of atrazine tested exceed those likely to be experienced in the natural aquatic environment suggesting that short term exposure to atrazine does not pose a risk to Atlantic salmon during the period of smoltification.

Population level effects of reduced fecundity in the fish species perch (Perca fluviatilis) and the implications for environmental monitoring

A 40% reduction in relative gonad size in perch (Perca fluviatilis) has been observed over that past two decades at the Swedish national reference site Kvädöfjärden. This biomarker response could be interpreted as a reduction in fecundity and increased risk of local extinction. However, abundance estimates from the same area has not provided any evidence of a reduction in population size. In the present study, a matrix population model was developed to investigate if a reduction in fecundity can be expected to have long term effects on population viability for perch and to evaluate the probability to detect such effects through abundance estimates. The model was parameterized from 17 years of population data from Kvädöfjärden as well as from other studies on perch. The model included density dependence and environmental stochasticity. The results indicated that a reduction in fecundity that is in level with the observed reduction in relative gonad size in Kvädöfjärden will cause a substantial risk for local extinction. The risk that the population will fall below 20% of the carrying capacity within 50 years is 44% when the fecundity is reduced by 40%. However, due to variability in abundance measurements it will take some time before a reduction in gonad size leads to statistically significant effects on the population. If the fecundity is reduced by 40% successively over a 10-year period, the probability to detect this through abundance estimates within 10 years is less than 50%. The results of the present study clearly show that relevant biomarkers have an important role in environmental monitoring as early warning signals, preferably in combination with measurements at higher levels of biological organization.

Influence of seasonal changes in relative liver size, condition, relative gonad size and variability in ovarian development in multiple spawning fish species used in environmental monitoring programmes

Basic biological information was collected to assist in understanding the biology of selected small‐bodied fishes for use in environmental monitoring programmes. Gonado‐somatic index (IG) and hepato‐somatic index (IH) profiles of female blacknose dace Rhinichthys atratulus, mummichog Fundulus heteroclitus and golden shiner Notemigonus crysoleucas were similar, decreasing gradually during the spawning season. IG and IH profiles of female northern redbelly dace Phoxinus eos peaked twice suggesting oocyte recruitment was continuous throughout the spawning season. Regressions of ovary mass to adjusted body mass (MA) were more variable in dace relative to the other fish species. For female blacknose dace, variability in the relationship between ovary mass and MA was minimized by selecting either 2 year‐old fish and fish that weighed 2–4 g.

Long-term monitoring of the health status of female perch ( Perca fluviatilis) in the Baltic Sea shows decreased gonad weight and increased hepatic EROD activity

Annual investigations of the health status of female perch ( Perca fluviatilis) were performed during 8–13 years in order to detect long-term, large-scale changes in the Baltic Sea. These background data are also meant to be used as baselines in recipient investigations at various point sources in the Baltic Sea. Fish were sampled at three coastal sites in Sweden: two in the Baltic Proper (since 1988) and one in the Bothnian Bay (since 1993). In all, 19 biochemical, physiological and histopathological variables were measured. By reflecting central functions of life, such as red blood cell functions, immune defence, liver function, biotransformation processes, intermediary metabolism, ion balance, and reproduction, the selected variables give a good picture of the health status of the fish. The most important observations were strong trends towards decreased gonadosomatic index (relative gonad size) and increased hepatic EROD activity in female perch in the Baltic Proper. Most of the other variables varied little between the years. The reduced gonad size and the EROD induction indicate that factors in the environment, e.g. the occurrence of pollutants, affect important physiological functions, such as reproduction and biotransformation processes, in fish even in a reference area in the Baltic Proper. It is urgent to make further studies in order to identify which pollutant(s) or other possible cause(s) are responsible for the observed biological effects.

Three Decades of Swedish Experience Demonstrates the Need for Integrated Long-Term Monitoring of Fish in Marine Coastal Areas

Abstract The first attempts to monitor coastal fish in Sweden were made in the 1960s and 1970s. Ecological, physiological, biochemical and environmental chemistry data were collected in separate projects. When the National Marine Monitoring Programme was revised in 1992, a new strategy was introduced for assessments of long-term trends in coastal fish communities. Annual integrated monitoring of contaminants, biomarkers and population and community indicators of ecosystem health was started in selected areas using common sentinel species. Data from one monitoring area at the coast of the Baltic proper are analyzed in this paper. The results have shown a shift in fish community structure indicating changes in ecosystem productivity. Trends have been detected in growth rate (positive) and relative gonad size (negative) in perch (Perca fluviatilis), suggesting a metabolic disturbance according to the predictive response model developed for interpretations. One factor which may have contributed to the reduced GSI was a decrease in mean age of sampled fish during the period of study. Chemical exposure was indicated by a 3-fold increase of EROD activity during the monitored 15-year period. However, concentrations of most measured contaminants in perch have decreased during the same period. The experience of the integrated approach has shown that a tentative analysis of cause and environmental significance could be made, improving the assessment, but there still remain unsolved questions to be answered in follow-up studies. The analysis has also shown the importance of long-term monitoring at several levels of biological organization to distinguish between natural variation and low-level effects on ecosystems.

Variation in Plasma Steroids and Reproductive Traits in Dimorphic Males of Corkwing Wrasse (Symphodus melops L.)

Differences in plasma steroid levels may reflect behavioral, gonadal, or morphological specializations that characterize different male reproductive phenotypes in teleost fishes. In the present study, we investigated whether differences in plasma steroid levels exist between two distinct male morphs shown in the corkwing wrasse Symphodus melops. In addition, we examined differences in male reproductive traits, including gonad mass, sperm motility, and sperm concentration, between the two male types. Possible associations between plasma steroid levels and reproductive traits were also investigated. The results indicated that males with typical male secondary sexual characters (territorial males) had higher plasma levels of 11-ketotestosterone (11kT) compared to smaller males with female secondary sexual characters (female mimics). The female mimics in turn had higher plasma levels of both testosterone (T) and 17β-estradiol. In addition, female mimics had relatively larger gonads and longer-lived sperm than territorial males. Relative gonad mass covaried significantly with the plasma levels of 11kT and T among the morphs, indicating that the relative gonad size correlates positively with the plasma level of these two steroids. However, there was no significant covariance between sperm traits and plasma steroids for the two male morphs. Hence, our results do not indicate any causal link between sperm quality and hormones.

Some data on the biology of common bream, Abramis brama (L., 1758), from the Międzyodrze waters

Growth rate (based on fry length measurements and back calculations), condition, relative gonad size, and length at first maturity were determined in the common bream population inhabiting Międzyodrze, a deltaic area situated in the vicinity of Szczecin.

Effects of temperature and food ration on gonad growth and oogenesis of the green sea urchin, Strongylocentrotus droebachiensis

To assess the effects of both temperature and food ration on gonad growth and oogenesis of the green sea urchin, Strongylocentrotus droebachiensis (O.F. Muller), individuals collected December 1996 (winter experiment) and June 1997 (summer experiment) were maintained for 3 months in one of four experimental treatments: (1) 3 °C and fed ad libitum (high ration), (2) 3 °C and fed one-seventh of the maximum ration (low ration), and (3) 12 °C and fed the high ration; (4) 12 °C and fed the low ration. All individuals were fed an artificial diet and exposed to only 1 h of light every day. At the end of both experiments, mean gonad indices of sea urchins fed the high ration had increased significantly (11–24% and 6–19% in the winter and summer experiments, respectively), while the gonad indices of individuals fed the low ration did not change. At the high ration (both experiments), the increase in gonad index of sea urchins occurred primarily as the result of a significant increase in the mass of nutritive phagocytes, as revealed by histological analyses. Primary oocytes were significantly larger in individuals held at 3 °C than at 12 °C throughout the winter experiment, regardless of food ration; during the summer experiment, primary oocytes were significantly larger in individuals receiving the high ration, regardless of the temperature at which they were held. These results suggest that: (1) food availability is the most important factor regulating energy storage and the relative size of gonads throughout the year, (2) temperature affects the rate of growth and maturation of primary oocytes during the later stages of oogenesis, and (3) once gametogenesis has been initiated, mature ova will be produced, even under conditions of low food availability. Conditions of high food availability in summer and low temperature in winter would thus favor reproductive output in sea urchin populations.