Sand Goby Research Articles

Should females prefer males with elaborate nests?

It is widely assumed that when males alone are responsible for nest building, nest characteristics should reflect the quality of its owner and that the nest itself should be an important cue in female choice. This, however, does not always have to be the case if, for example, nest attributes are an unreliable reflection of male quality. Here, we investigate whether females should prefer nest characteristics in a small marine fish, the sand goby, Pomatoschistus minutus. Previous findings suggest that female sand gobies prefer males that possess well-built nests (based on the amount of sand piled on top). It was unclear, however, whether females chose males based on the quality of the nest per se or some other, correlated quality of the builder. In the current study, we found conflicting evidence of whether males in good condition are able to bring a greater percentage of eggs to the hatching stage. In a field investigation, we also found that the relationship between body condition and the degree of nest construction was temporally unstable. Furthermore, when we experimentally disentangled nest quality from other male traits, we showed that females did not prefer to spawn with males that had the most elaborate nests. Together, these results suggest that females do not necessarily prefer males based on nest characteristics and may, instead, rely on multiple cues when choosing mates, the relative importance of which should vary depending on context. Copyright 2009, Oxford University Press.

Relative costs of courtship behaviours in nest-building sand gobies

Courting males often use multiple signals to advertise their quality to females. Assuming that courtship traits are energetically costly, one would expect a limit to the overall courtship effort of an individual and that a high courtship effort takes its toll on individual condition. We tested this experimentally using a small marine fish, the sand goby, Pomatoschistus minutus, whose males attract females through courtship displays and well-built nests (mussel shells covered with sand). At the end of a 5-day period of supplemental food, or repeatedly induced courtship or construction of nests (or none of these, as a control), we tested whether male display intensity, nest quality (nest cover and nest opening size) and body condition were affected. Males provided with food in excess were in significantly better condition and had significantly higher nest quality than control males. Display rate, however, was not significantly affected by feeding regime. Fish that had been manipulated to perform increased courtship or nest building did not suffer in terms of reduced condition, display rate or nest quality. However, individual fish that displayed intensely after treatment also built better-covered nests. Both of these traits are important in female choice. Moreover, fish that displayed intensely before the treatment continued to do so after treatment, a result that is compatible with signalling of genetic or phenotypic quality. Our results suggest that (1) nest cover is an honest signal of male condition, although we found no cost of nest building per se and (2) courtship display does not signal male condition.

Females decide whether size matters: plastic mate preferences tuned to the intensity of male–male competition

Recent studies have indicated that mating success of large males may improve under increasing levels of mating competition. This outcome is explained 1) if male mating competition is overriding female preferences for male traits that are unrelated to, or negatively correlated with, male size and dominance and, in so doing, dictates the distribution of matings or 2) if females alter their preferences with respect to large males when male–male competition is intense. Under both hypotheses, one could expect large, dominant males to be more successful under intense competition than under weak competition. However, only the first explanation predicts that male mating success under intense competition should be determined by dominance; traits that are unrelated to male dominance should be uncorrelated to mating success. In contrast, if females change their preferences (explanation 2), males with traits beneficial to females independent of the competitive environment can maintain a high mating success under all levels of male–male competition. We tested these alternatives using a small marine fish, the sand goby, Pomatoschistus minutus. The mating success of large males increased under conditions allowing intense male competition, whereas females showed a preference for good nest building independent of the level of competition. These findings suggest that females are in control of their choice by altering their preference for male size in response to the intensity of male–male competition rather than female preference being overshadowed by male dominance. This plasticity of preferences implies that the strength of sexual selection is not constant at the population level. Key words: adaptive mate choice, mating competition, phenotypic plasticity, Pomatoschistus minutus, sexual selection. [Behav Ecol]

Estuarine recruitment of a marine goby reconstructed with an isotopic clock

Information on movement patterns of marine fishes between estuarine populations and stocks at sea is fundamental to understanding their population dynamics, life history tactics and behavior. Furthermore, understanding estuarine habitat use by marine fishes is crucial for their effective conservation and integrated estuarine management. Although large numbers of young marine fish make use of temperate estuaries in highly predictable abundance patterns, very little is known about how estuarine populations interact with the populations at sea. Recruitment of sand goby Pomatoschistus minutus (Pallas, 1770) into the low salinity zone of the Scheldt estuary (Belgium) was reconstructed over an entire year by means of an isotopic clock. These results were combined with a growth model to yield age and length at immigration. Sand gobies entered the upper Scheldt estuary almost continuously from May onwards, except in July when they appeared to avoid the estuary due to warm summer temperatures. About 70% of the fish caught in the upper estuary resided there for less than 1 month, which indicates a strong temporal overlap of immigration and emigration. This complex migration pattern suggests that estuarine residence is caused by trade-offs made at the individual level, whereby migration is probably triggered by temperature. The high turnover of individuals in the estuarine population leads us to question the functional role of the estuary for marine fishes. Sand gobies entering the upper estuary had a wide range of ages and body sizes, although they were at least 2 months old and had a minimum standard length of approximately 20 mm. This study shows that the use of an isotopic clock strongly complements catch data and is useful to describe the connectivity between populations.

Male Nest Choice in Sand Gobies, Pomatoschistus minutus

AbstractAlthough material resources can have a direct bearing on the fitness of both sexes, few studies have actually examined resource‐based preferences from a male choice perspective. In sand gobies, Pomatoschistus minutus, the size of a male’s nest influences his attractiveness to females and also dictates the number of eggs he can receive. Thus, one might expect males to prefer larger nests. However, an earlier study of marine sand gobies from a population with a surplus of nest sites and high nest predation found that males exhibited size‐assortative nest preferences. Here, we investigated male nest preferences from a brackish population characterised by a chronic nest shortage but lower predation risk. A survey of naturally settled nests in the field (shells and rocks) showed a pattern of size‐assortative nest occupancy consistent with the previously studied population, with larger males occupying larger (i.e. rock) nests. However, when offered a choice of potential nests in the absence of male competition, we found that all male gobies in our population, irrespective of their own body size, actually preferred larger nests. Moreover, a predilection towards large nests superseded any preferences based on nest colour. Our results not only indicate the existence of male preferences for material resources but, considered in the light of previous work, also suggest that such preferences may vary among populations and, importantly, may not necessarily be realised in a competitive setting.

Cannibalize or care? The role of perceived paternity in the sand goby, Pomatoschistus minutus

Parental care is a costly part of reproduction. Hence, natural selection should favor males which avoid caring for unrelated young. However, the decision to abandon or reduce care requires cues which are evaluated to give information on potential reproductive value of the offspring. The prediction that male sand gobies, Pomatoschistus minutus, care for foreign eggs as long as they were spawned in their own nest and at least some of such cues are fulfilled was tested. Egg-guarding males that had recently taken part in a spawning event were given a clutch of eggs that was sired either by themselves or another male, in either their own or another male’s aquarium. Males that had not taken part in a spawning event were used as controls and were given eggs sired by another male. We measured the amount of filial cannibalism and nest building. Control group males did not care for eggs and ate them all before rebuilding the nest. In the other treatments, there were no significant effects of paternity, though males moved to another male’s aquarium increased their clutch area threshold and completely consumed larger clutches than males that were not moved. There was no intermediate response in any treatment in the form of increased partial filial cannibalism or less well-constructed nests. Our results suggest that egg-guarding males cannot distinguish between eggs sired by themselves and those sired by other males but are able to react to cues indicating paternity state. Males do not adopt eggs to attract females in P. minutus.

Hurry-up and hatch: selective filial cannibalism of slower developing eggs

Filial cannibalism (the consumption of one's own offspring) is thought to represent an adaptive strategy in many animals. However, little is known about the details of which offspring are consumed when a parent cannibalizes. Here, we examined patterns of within-brood filial cannibalism in the sand goby (Pomatoschistus minutus). Males spawned sequentially with two females, and we asked whether males cannibalized selectively with regard to egg size or the order in which eggs were received. Males preferentially consumed the larger eggs of the second female they spawned with. Because larger eggs took longer to hatch, and because female 2's eggs were up to 1 day behind those of female 1, such preferential cannibalism might allow males to decrease the time spent caring for the current brood and re-enter the mating pool sooner. More work is needed to understand the fitness consequences of such selective cannibalism.

Daily activity pattern of the sand goby, Pomatoschistus minutus (Pisces), at low light intensity

In autumn and winter, the sand goby (Pomatoschistus minutus) in the Baltic Sea is to a large extent found on soft bottoms deeper than the summer thermocline. Although P. minutus are numerous during a large part of the year in these areas, most studies on this species have been performed on very shallow bottoms. Here we study the activity of P. minutus in autumn using video recordings in the laboratory, under light (1.5-2 lux) and temperature conditions prevailing at ca. 30 m depth. We propose that the results can be used to evaluate in situ abundance censuses. P. minutus had the same nocturnal activity pattern in low light intensity as described for light intensities found in shallow water. The fish swim significantly more in darkness than in light, and bury in the sediment mainly at day. These behaviours, recorded in the absence of predators, are suggested to be adaptations to avoid predators.

Paternal care behaviour of sand gobies is determined by habitat related nest structure

Summary This study examines the effects of habitat-dependent nest structure on male parental behaviour in a small marine fish, the sand goby (Pomatoschistus minutus). In the northern Baltic, the sand goby breeds in two different habitats: on soft sand bottoms and on rocky beaches. We compared in laboratory conditions the behaviour of nest-guarding males occupying either a typical sand or rock habitat nest. We found that males with a rock habitat nest fanned their eggs considerably less and with shorter bouts than males in the sand habitat treatment. Hence, our study shows that nest structure can be an important factor determining parental care behaviour. The differences in nest structure may result in divergent selection pressures on male sand gobies occupying the two habitats.

Male painted gobies (Pomatoschistus pictus) vocalise to defend territories

Summary Many fish species emit sounds in agonistic contexts. During direct confrontations sounds are typically produced during the display phase in conjunction with visual exhibitions. Here we studied sound production during territorial defence in captive painted gobies, Pomatoschistus pictus, and related acoustic parameters with male traits and the date of recording (Julian day, i.e., with the approach of the peak of the breeding season). Territorial males emitted drumming sounds during displays that involved darkening the chin and fins, spreading fins and quivering the body. Drums were trains of low frequency pulses (≈23 pulses) repeated every 27 ms and usually lasting under a second. Drums were produced in short sequences of sounds (bursts). All acoustic parameters differed significantly among males. Drum and burst duration, and drum number of pulses increased significantly with male size. Calling duration (including drum, burst duration and drum number of pulses) also increased significantly with Julian date and presented a high intra-male variability, suggesting that these parameters may also depend on the individual’s motivation. We provide the first report for agonistic sound production in sand gobies and give evidence that sound parameters contain information that can be used during mutual assessment in contests over territories.

Effect of digestion on the δ13C and δ15N of fish‐gut contents

Gut contents of sand goby Pomatoschistus minutus showed higher C and N isotope values than the food before consumption. This enrichment was more pronounced in the hindgut than in the foregut, probably because of preferential assimilation of 12C and 14N along the gastro‐intestinal tract. The results indicated that the shift towards higher values in the alimentary canal occurs in the first 2 h after feeding.

Estuarine production of resident and nursery fish species: Conditioning by drought events?

The production of resident ( Pomatoschistus minutus and Pomatoschistus microps) and marine juvenile fish species using the Mondego estuary (central Portugal) as nursery grounds ( Dicentrarchus labrax, Platichthys flesus, Solea solea), was assessed in order to: (1) understand the potential of the estuary for fish production; (2) know the production of nursery fish species likely to be exported to the coastal stocks; and (3) how anthropogenic and natural stress could influence the estimated production. Sampling occurred from June 2003 to May 2006 and together the 5 species in study comprised around 70% of the whole fish community numbers and biomass. Increasing drought conditions were observed, starting with a normal hydrological year in 2003 until attaining a severe drought in 2005, which resulted in low river discharges (1/3 of the mean river discharges in 2003). Additionally, high water temperatures were observed in 2003 and 2005 (24 and 26 °C, night temperatures). The secondary production was estimated using the increment summation method, after recognition of the cohorts. Production was in general lower in the Mondego estuary when compared to other systems, which was associated to the estuary's small area (only 3.4 km 2, less than 1/4 of area compared to other studied systems). Dicentrarchus labrax was among the most productive species. Production decreased in the drought year for all species, especially evident for D. labrax, P. minutus and P. flesus. No direct effects could be attributable to the salinity and temperature variations and to the low freshwater discharges (resulting from the drought and high temperatures), yet these were pointed as probable major reasons for the decreased production. A significant reduction (15–45% reduction in the estuarine production) was also concluded for the potential production to be exported for coastal areas by the nursery species in the drought conditions.

Repeatability of mating preferences in the sand goby

Variation among individuals in mate choice has important implications for the evolution of sexually selected traits. For example, it offers an explanation for the continued existence of heritable genetic variation in sexually selected male traits. In this study, we first tested the suitability of association tests for assessing female mate preferences in the sand goby, Pomatoschistus minutus. Sand goby females showed sexually motivated association preferences that were repeatable and corresponded to actual mating decisions. We then compared the correlation between the preferences of two different females presented to the same male pair with the correlation between preferences of single females tested twice. We found a weak correlation between preferences in the two-female treatment, while the correspondence between preferences was much higher for the single-female treatment. These results are in accordance with the possibility that sand goby females show genetically based, individual differences in mate preferences.

The fish assemblage of the Mondego estuary: composition, structure and trends over the past two decades

The fish assemblage of the Mondego estuary was studied from June 2003 to May 2004. Five areas with different environmental conditions were sampled monthly, using a 2 m beam trawl (5 mm mesh size at the cod end). To complement information, sampling was also performed, seasonally, using a 7 m otter trawl with a 10 mm mesh size. Thirty-two species were identified. Dicentrarchus labrax, Pomatoschistus microps, Pomatoschistus minutus, Solea solea, Platichthys flesus and Diplodus vulgaris were the most abundant species. Marine juvenile migrants had the highest number of species, thirteen, followed by estuarine residents with eight species. Marine species that use the estuary as nursery grounds were the most abundant in terms of density and biomass. In spring and summer, juveniles occur in the upper, oligohaline areas, but afterwards, in autumn and winter, they tend to disperse to the middle and lower areas, with higher marine influence. Comparing the results obtained in this study with those reported in the early 1990’s, a marked decrease in species richness can be noticed, which is probably due to anthropogenic factors, namely an increase in depth of the main channel and intense euthrophication processes in the middle and upper areas.

Strategies of Pomatoschistus minutus and Pomatoschistus microps to cope with environmental instability

The populations of Pomatoschistus minutus and Pomatoschistus microps were studied from June 2003 to May 2006 in the Mondego estuary, in order to understand the ability of these species to withstand environmental variability. During this period a severe drought occurred (2005), with consequent lower freshwater runoff and higher salinity incursion into the estuary. Occasional abnormal high water temperatures were observed in 2003 and 2005. The fish populations were sampled monthly along an estuarine gradient, from which population density, structure, growth and biomass production was assessed. Pomatoschistus minutus distributed mainly at the most saline downstream area, while P. microps distributed within the whole estuary, in accordance to the salinity and temperature tolerances for the species. A clear decrease in density and production was observed for P. minutus in the dry year, with non-expressive recruitments and the quick disappearance of the parental cohort. For P. microps, the decrease was not so pronounced. No direct effects were attributable to the salinity and temperatures variations (resulting from the drought and high temperatures). Yet, higher predation pressure on P. minutus hypothesis was raised, as the salinity incursion increased the piscivorous marine adventitious species in the downstream areas. Pomatoschistus microps benefited from a wider temperature and salinity range tolerance, allowing the species to occupy different areas in the estuary and by this seemed better able to cope with the environmental conditionings during the 3-year studied period.

Mate preference for multiple cues: interplay between male and nest size in the sand goby, Pomatoschistus minutus

Female mating preferences are often based on more than one cue. In empirical studies, however, different mate choice cues are typically treated separately ignoring their possible interactions. In the current work, we studied how male body size and size of the male’s nest jointly affect mate preferences of female sand gobies, Pomatoschistus minutus. The females were given a binary choice between males that differed either in body size or size of their nest or both. We found that neither body size nor size of the nest alone affected male attractiveness, but together these 2 cues had a significant effect. Specifically, large males were more popular among females when they had a large nest than when they occupied a small nest. The results suggest that if interaction effects between multiple mate choice cues are not considered, there is a danger of ignoring or underestimating the importance of these cues in sexual selection by female choice. Key words: mate choice, multiple cues, nest size, Pomatoschistus minutus, sexual selection. [Behav Ecol]

Visual pigments of Baltic Sea fishes of marine and limnic origin

Absorbance spectra of rods and some cones were measured by microspectrophotometry in 22 fish species from the brackish-water of the Baltic Sea, and when applicable, in the same species from the Atlantic Ocean (3 spp.), the Mediterranean Sea (1 sp.), or Finnish fresh-water lakes (9 spp.). The main purpose was to study whether there were differences suggesting spectral adaptation of rod vision to different photic environments during the short history (<10(4) years) of postglacial isolation of the Baltic Sea and the Finnish lakes. Rod absorbance spectra of the Baltic subspecies/populations of herring (Clupea harengus membras), flounder (Platichthys flesus), and sand goby (Pomatoschistus minutus) were all long-wavelength-shifted (9.8, 1.9, and 5.3 nm, respectively, at the wavelength of maximum absorbance, lambda(max)) compared with their truly marine counterparts, consistent with adaptation for improved quantum catch, and improved signal-to-noise ratio of vision in the Baltic light environment. Judged by the shape of the spectra, the chromophore was pure A1 in all these cases; hence the differences indicate evolutionary tuning of the opsin. In no species of fresh-water origin did we find significant opsin-based spectral shifts specific to the Baltic populations, only spectral differences due to varying A1/A2 chromophore ratio in some. For most species, rod lambda(max) fell within a wavelength range consistent with high signal-to-noise ratio of vision in the spectral conditions prevailing at depths where light becomes scarce in the respective waters. Exceptions were sandeels in the Baltic Sea, which are active only in bright light, and all species in a "brown" lake, where rod lambda(max) lay far below the theoretically optimal range.

Effect of Triiodothyronine and Cortisol on Development, Growth and Survival Rate of Sand Goby (Oxyeleotris marmorata, Blkr.) Larvae

&lt;p class="MsoBodyText2" style="text-indent: 0cm;"&gt;&lt;span style="font-size: 10pt;" lang="in" xml:lang="in"&gt;ABSTRACT&lt;br /&gt;&lt;/span&gt;&lt;/p&gt;&lt;p class="MsoBodyText2" style="text-indent: 0cm;"&gt;&lt;span style="font-size: 10pt;" lang="in" xml:lang="in"&gt;This experiment was conducted to investigate the effect of triiodothyronine and cortisol on the development, growth, and survival rate of sand goby larvae.&lt;span&gt; &lt;/span&gt;The experiment was carried out at Kolan Percobaan Babakan, Faculty of Fisheries and Marine Sciences, IPB Bogor.&lt;span&gt; &lt;/span&gt;The larvae were immersed in solution of A (T&lt;sub&gt;3&lt;/sub&gt; 2 mg/1 + C 1 mg/1), B (T&lt;sub&gt;3&lt;/sub&gt; 2 mg/1 + C 0, 1 mgll), C (T&lt;sub&gt;3&lt;/sub&gt; 2 mg/1 + C 0,0 1 mg/1) dan D (without hormone) for one hour.&lt;span&gt; &lt;/span&gt;After treatment, larvae were reared in aquarium (50x50x50 cm).&lt;span&gt; &lt;/span&gt;Larvae were fed by rotifer and phytoplankton, three times a day.&lt;span&gt; &lt;/span&gt;Larval development, growth and survival rate were observed.&lt;span&gt; &lt;/span&gt;Result showed that T&lt;sub&gt;3&lt;/sub&gt; 2 mg/1 +C 1 nig/1 and T&lt;sub&gt;3&lt;/sub&gt; 2 mg/1 + C 0, 1 mg/1 could accelerated development of swim bladder and eyespot of larvae.&lt;span&gt; &lt;/span&gt;Treatment did not effect body pigmentation and growth; but effect survival rate of sand goby larvae.&lt;/span&gt;&lt;/p&gt;&lt;p class="MsoNormal" style="text-align: justify;"&gt;&lt;span lang="in" xml:lang="in"&gt;Key words :&lt;span&gt; &lt;/span&gt;Triidothyronine, cortisol, larvae, sand goby fish, development, growth, survival rate&lt;/span&gt;&lt;/p&gt;&lt;p class="MsoNormal" style="text-align: justify;"&gt;&lt;span lang="in" xml:lang="in"&gt; &lt;/span&gt;&lt;/p&gt;&lt;p class="MsoNormal" style="text-align: center;" align="center"&gt;&lt;span lang="in" xml:lang="in"&gt;ABSTRAK&lt;/span&gt;&lt;/p&gt;&lt;p class="MsoNormal" style="text-align: justify;"&gt;&lt;span lang="in" xml:lang="in"&gt;Penelitian ini bertujuan untuk mengetahui pengaruh pemberian hormon triidotironin dan kortisol terhadap perkembangan, pertumbuhan dan kelangsungan hidup larva ikan betutu.&lt;span&gt; &lt;/span&gt;Penelitian ini dilakukan di Kolam Percobaan Babakan, Fakultas Perikanan dan Ilmu Kelautan, Institut Pertanian Bogor.&lt;span&gt; &lt;/span&gt;Larva direndam selama satu jam dalam larutan A (T&lt;sub&gt;3&lt;/sub&gt; 2 mg/1 + C 1 mg/1), B (T&lt;sub&gt;3&lt;/sub&gt; 2 mg/1 + C 0, 1 mg/1), C (T&lt;sub&gt;3&lt;/sub&gt; 2 mg/1 + C 0,0 1 mg/1) dan D (tanpa hormon).&lt;span&gt; &lt;/span&gt;Setelah perlakuan, larva dipelihara dalam akuariun berukuran 50x50x50 cm.&lt;span&gt; &lt;/span&gt;Selama pemeliharaan larva diberi pakan berupa rotifer dan fitoplankton dengan frekuensi tiga kali sehari.&lt;span&gt; &lt;/span&gt;Perkembangan, petumbuhan, dan kelangsungan hidup larva diamati.&lt;span&gt; &lt;/span&gt;Perendaman larva ikan betutu dalam larutan A dan B dapat mempercepat pembentukan gelembung renang dan bintik mata.&lt;span&gt; &lt;/span&gt;Perlakuan yang diberikan tidak mempengaruhi kecepatan terjadinya pigmentasi tubuh dan pertumbuhan, tetapi mempengaruhi derriat kelangsungan hidup larva.&lt;/span&gt;&lt;/p&gt;&lt;p class="MsoNormal"&gt;&lt;span lang="in" xml:lang="in"&gt;Kata kunci :&lt;span&gt; &lt;/span&gt;Triidotironin, kortisol, larva, ikan betutu, perkembangan, pertumbuhan, kelangsungan hidup&lt;/span&gt;&lt;/p&gt;

Mate compatibility, parental allocation and fitness consequences of mate choice in the sand goby Pomatoschistus minutus

Recent theory and empirical work suggests that there may be variation among females in mate preferences that is adaptive. One of the possible mechanisms maintaining variability in preferences and preferred traits is that the benefits of mate choice may depend on compatibility with potential mating partners. We examined fitness consequences of mate choice in a species of fish, the sand goby, Pomatoschistus minutus with a special focus on mate compatibility. Females were given the opportunity to establish their mate preferences in a dichotomous mate choice experiment. This information was then applied by mating the focal or control female with either the preferred or the non-preferred male. The parental performance of the males of these four mating combinations was then measured. In a separate experiment, we assessed the female differential allocation by determining the residual gonad weight of spawned females as a measure of the proportion of eggs spawned. We also estimated the amount of filial cannibalism separately for both sexes. Our results show that preferred males provided benefits in the form of an increased number of hatching eggs. This benefit was the same when the male was mated with a focal or a control female. Hence, we found no support for benefits that depend on mate compatibility. Neither did we find support for the hypothesis that females would lay a different number of eggs depending on the male status. The results also indicate that male filial cannibalism has a strong role in determining hatching success in this species.

Bioindicators and reproductive effects of prolonged 17β-oestradiol exposure in a marine fish, the sand goby ( Pomatoschistus minutus)

The effects of 17β-oestradiol (E2) on mortality, growth rates, sexual maturation, hepatic vitellogenin (VTG) mRNA expression and reproductive success were investigated during an 8-month, water-borne exposure of a marine fish, the sand goby ( Pomatoschistus minutus). Indicators of oestrogenic exposure were investigated as predictors of population-level reproductive success. E2 exposure concentrations were <5 (below limit of detection), 16 ± 3, 97 ± 20 and 669 ± 151 ng l −1 (bootstrap means and standard errors). The carrier solvent (<20 μl l −1 propan-2-ol) significantly reduced the rate of egg production compared to untreated fish, but did not significantly affect male VTG mRNA expression, brood size, or the other studied parameters. Fish exposed to 16 ng l −1 E2 showed few adverse effects compared with solvent only-exposed fish. Exposure to 97 ng l −1 E2 significantly inhibited male sexual maturation, induced male VTG mRNA expression and delayed spawning. The 97 ng l −1 E2 exposed population also produced fertile eggs at a significantly slower rate than solvent controls; however, brood size, fertility and overall reproductive success were not significantly affected. Exposure to 669 ng l −1 E2 significantly increased mortality, adversely affected haematological parameters and caused an almost total lack of reproductive activity, with both sexes failing to mature. Reproductive failure following exposure to 669 ng l −1 E2 was evident in both sexes when crossed with untreated animals. This work indicates that marine fish are similarly as sensitive to oestrogenic exposure as freshwater fish, that exposure biomarkers such as VTG are more sensitive to exposure than are reproductive effects, and that the use of carrier solvents in long-term reproductive studies should be avoided.