Participatory fishery monitoring is successful for understanding the reproductive biology needed for local fisheries management

Tropical fisheries management should rely on reproductive biology to inform management regulations; however, this information is often lacking and can be highly variable over in space and time. It is unfeasible for many fisheries, especially data-poor ones that are typical of tropical reefs to collect the necessary information on reproductive biology. One solution is a participatory approach where local fishers, scientists, and regulating agencies gather the necessary information to assess population variability for important management metrics such as size at maturity, reproductive output, and spawning seasons. Through collaborations with local fishers, we developed a monitoring program to gather population-level information on the reproductive characteristics of the convict tang, Acanthurus triostegus sandvicensis. We examined four locations across the main Hawaiian Islands and found size at maturity [size at which 50% of individuals are mature (L₅₀)] to vary among locations, with interpopulation differences in maturity?~?20% of the fish’s total length. Larger individuals produced more eggs and spawned more often than smaller individuals. A semilunar spawning pattern was observed, with group spawning occurring near the new and full moons. However this pattern was variable by year and location, likely resulting from different seasonal peaks in spawning by location. Gonadosomatic index (t?=?2.41, p-value?=?0.02) and spawning fraction (z?=?2.92, p-value?<?0.01) were both significantly higher in 2014 compared to 2013, suggesting annual variability in reproductive output. Participatory fishery monitoring proved successful in collecting biological needed for management and improved understanding of population reproductive variability.     

Ulva lactuca and U. flexuosa (Chlorophyta,Ulvophyceae) cultivation in Brazilian tropical waters: recruitment,growth, and ulvan yield

Ulva spp. are used in a wide range of commercial applications, including bioremediation, food, bioenergy, pharmaceuticals, and agriculture. The sulfated polysaccharide ulvan obtained from Ulva spp. is of interest for triggering plant defenses against disease. However, the cultivation of Ulva spp. is still in its infancy. This study verified the feasibility of cultivating Ulva lactuca and Ulva flexuosa at two sites on the tropical Brazilian coast. We investigated the following: (a) methods to induce sporulation, (b) comparison of seeding ropes inoculated in vitro versus seeding at sea over 40 days, (c) production and harvest cycles at 15 and 30 days, (d) growth productivity of U. flexuosa at sea and in outdoor tanks, and (e) comparison of ulvan yields from biomass cultivated in tanks and the sea. High nutrient treatment was the most efficient method to induce sporulation (7,540?±?3,133 spores m^?1). Sea-based cultivation of U. flexuosa was only successful at one site. Seeding of ropes in vitro was more efficient than seeding at sea (0.31?±?0.20 g m^?2 day^?1), and 15-day harvest cycles were most efficient (20.1?±?1.8 % day^?1; 0.46?±?0.11 g m^?2 day^?1). Despite differences in plant growth in tanks (27.9?±?4.4 % day^?1) and at sea (20.1?±?1.8 % day^?1), the dry biomass and ulvan yields (17.7?±?5.0 %) did not differ between these systems. Cultivation of U. flexuosa was feasible at sea using in vitro seeding with a production cycle of 15 days in Brazilian tropical waters and tanks with high irradiance and enriched seawater.     

Mass spawning of corals on a high latitude coral reef

Evidence is presented that at least 60% of the 184 species of scleractinian corals found on reefs surrounding the Houtman Abrolhos Islands (Western Australia) participate in a late summer mass spawning. These populations are thus reproductively active, despite most species being at the extreme southern limit of their latitudinal range (28° 29°S). In the present study, coral mass spawning occurred in the same month on both temperate (Houtman-Abrolhos) and tropical (Ningaloo) reefs of Western Australia, despite more than two months difference in the timing of seasonal temperture minima between the two regions. This concurrence in the month of spawning suggests that temperature does not operate as a simple direct proximate cue for seasonal spawning synchrony in these populations. Seasonal variation in photoperiod may provide a similar and more reliable signal in the two regions, and thus might be more likely to synchronize the seasonal reproductive rhythms of these corals. Also there is overlap in the nights of mass spawning on the Houtman Abrolhos and tropical reefs of Western Australia, despite significant differences in tidal phase and amplitude between the two regions. This indicates that tidal cycle does not synchronize with the night(s) of spawning on these reefs. Spawning is more likely to be synchronised by lunar cycles. The co-occurrence of the mass spawning with spring tides in Houtman Abrolhos coral populations may be evidence of a genetic legacy inherited from northern, tropical ancestors. Micro-tidal regimes in the Houtman Abrolhos region may have exerted insufficient selective pressure to counteract this legacy.     

Reproductive Aspects of a Tropical Population of the Fiddler Crab Uca annulipes (H. Milne Edwards, 1837) (Brachyura: Ocypodidae) at Costa Do Sol Mangrove, Maputo Bay, southern Mozambique

Uca annulipes(H. Milne Edwards) is the dominant fiddler crab inhabiting mangrove forests in East Africa. However, several aspects concerning its reproduction are poorly known. Such information is necessary for a better understanding of several biological aspects occurring in this species. The aim of this study was to assess the reproductive biology of Uca annulipes as well as some factors determining its breeding season. Samplings were undertaken from January to December 2002 at Costa do Sol, a tropical mangrove forest around Maputo Bay, southern Mozambique. Crabs were randomly sampled, measured for carapace width (CW) and checked for the presence of eggs on female pleopods. Like most tropical brachyurans, Uca annulipes follows a continuous reproduction throughout the year with peaks of spawning during summer season and low frequency of egg-bearing females during winter. The frequency of ovigerous females was correlated with the air temperature (r ²= 0.652, p < 0.05) and rainfall (r ²= 0.897, p < 0.001), with the last parameter being the most important factor regulating the reproductive activity of this crab.     

Effect of seawater temperature on reproductive seasonality and fecundity of Pseudoplexaura porosa (Cnidaria: Octocorallia): latitudinal variation in Caribbean gorgonian reproduction

Abstract. The majority of tagged colonies of Pseudoplexaura porosa in Bermuda were reproductive over 2 months in the summer. They spawned 5–8 d after the full moon, with a peak on the sixth day, similar to colonies in Panama. The months of spawning were August and September in 1998, but July and August in 1999 and 2000. This temporal difference between the months of spawning corresponded to inter-annual variations in seawater temperature profiles. Initial gamete development each year occurred only when the daily mean seawater temperature during the month before spawning exceeded 27°C. There was a significant positive relationship between reproductive effort (gamete volume) of colonies and rising seawater temperature in the month preceding spawning; this was true for both the initial and the second spawning months. The end of the reproductive season each year was triggered by the decline in seawater temperature past the summer maximum. The duration of the reproductive season of conspecifics at the central Caribbean reef of Panama is 2 months longer than in Bermuda. This can be explained by the smaller annual temperature range at the lower latitude and the earlier onset of temperatures favorable for gamete development. Fecundity estimates for members of P. porosa (mean oocyte and spermary densities) in Bermuda were lower than for conspecifics in Panama. The shorter reproductive season in Bermuda, in addition to the lower fecundity of colonies, indicates that reproduction in P. porosa is compromised at this high latitude reef.     

Phenotypic plasticity in age and size at maturity and its effects on the integrated phenotypic expressions of life history traits of Cardamine flexuosa (Cruciferae)

We analyzed variation in phenotypic plasticity of life history traits between two Cardamine flexuosa populations based on differences in plasticity of age and size at maturity. C. flexuosa (Cruciferae) is a facultative, vernalization-sensitive, long-day annual, and its phenology and the phenotypic expressions of many life history traits are largely controlled by photoperiod and vernalization in natural populations. We used plants from two populations which differed in their responses to chilling and photoperiod treatments. The timing of developmental processes was changed by controlling temperature and photoperiod regimes in growth chambers. Plasticity in size at maturity was analyzed as changes in a growth trajectory using two parameters, age at maturity (Δt) and growth rate (k). Both traits showed plasticity, but differences between the populations were found mostly for Δt. Distinctive differences in size at maturity of individuals in the two populations were mainly due to different amounts of plasticity in Δt. Variations in plasticity of nine other life history traits and their associations to age and size at maturity were also analyzed. Variation for eight of the traits can be described, at least in part, as a function of age and size at maturity for both populations, and most of the variation in the total number of seeds was explained by age and size at maturity. Only age at maturity had any effect on changes in resource allocation. The nine life history traits were integrated through associated character expressions with age and size at maturity. Changes in the association between a trait and age and/or size at maturity were rather conservative compared to changes in the plasticity of a trait between the two populations. Associations with age and size at maturity are mostly explicable in terms of inherent relationships in the developmental processes, and they may limit the ecological range expansion and the adaptive evolution of plasticity in C. flexuosa. The negative correlation between reproductive allocation and age at maturity can be a cost of delaying maturation in C. flexuosa.     

Age,growth and reproduction of non‐native largemouth bass Micropterus salmoides (Lacépède, 1802) populations in two temperate African impoundments

This study aims to improve the understanding of the establishment success of Micropterus salmoides by assessing growth, maturity and reproductive seasonality of two populations from the temperate region in South Africa. Results are compared to those from other populations to test previously proposed hypotheses that the (i) extent of the spawning season, (ii) longevity, and (iii) growth performance are environmentally temperature dependent. Micropterus salmoides were sampled monthly between March 2010 and March 2012 from Wriggleswade and Mankazana impoundments using either angling or multi‐meshed (35, 45, 47, 57, 65, 73, 77, 93, 106, 118, 150 and 153 mm) multifilament gillnet fleets, and a 1 m seine net. The assessed populations in South Africa performed as expected compared to other introduced populations. Age at maturity (1.3–2 years) and length at maturity (232–254 mm FL) were similar to other temperate populations. A well‐defined, spring spawning season conformed to findings in other temperate populations. Using sectioned sagittal otoliths it was shown that fish were long‐lived (14 years). Growth rates differed significantly between the two assessed populations but both were slower growing than tropical and subtropical introduced populations. Growth performance (Φ′: 2.77–2.99) was similar to other temperate populations. These results indicate that the biology of introduced M. salmoides populations in South Africa is comparable to those of other temperate populations and supports the environmental temperature‐dependent hypothesis.     

A phylogenetic analysis of egg size,clutch size,spawning mode,adult body size,and latitude in reef fishes

Theoretical treatments of egg size in fishes suggest that constraints on reproductive output should create trade-offs between the size and number of eggs produced per spawn. For marine reef fishes, the observation of distinct reproductive care strategies (demersal guarding, egg scattering, and pelagic spawning) has additionally prompted speculation that these strategies reflect alternative fitness optima with selection on egg size differing by reproductive mode and perhaps latitude. Here, we aggregate data from 278 reef fish species and test whether clutch size, reproductive care, adult body size, and latitudinal bands (i.e., tropical, subtropical, and temperate) predict egg size, using a statistically unified framework that accounts for phylogenetic correlations among traits. We find no inverse relationship between species egg size and clutch size, but rather that egg size differs by reproductive mode (mean volume for demersal eggs = 1.22 mm³, scattered eggs = 0.18 mm³, pelagic eggs = 0.52 mm³) and that clutch size is strongly correlated with adult body size. Larger eggs were found in temperate species compared with tropical species in both demersal guarders and pelagic spawners, but this difference was not strong when accounting for phylogenetic correlations, suggesting that differences in species composition underlies regional differences in egg size. In summary, demersal guarders are generally small fishes with small clutch sizes that produce large eggs. Pelagic spawners and egg scatterers are variable in adult and clutch size. Although pelagic spawned eggs are variable in size, those of scatterers are consistently small.     

Genetic divergence and isolation by distance in the West Atlantic sea anemone Actinia bermudensis (McMurrich, 1889)

The sea anemone Actinia bermudensis [Proc. Acad. Nat. Sci. Philadelphia 41 (1889) 102] has a widespread distribution over the Western Atlantic, where it has been reported from Bermuda and Bahamas to southern Brazil. Nonetheless, reproductive features of this species, which broods asexually produced offspring, suggest that it has low dispersal capabilities. This raises a question about the specific status of the Brazilian population of A. bermudensis. The aim of this paper was to evaluate the taxonomic status of the Brazilian population, by genetically comparing it with the type locality (Bermuda) population. For this, we used allozyme electrophoresis to analyze samples from both populations. Thirteen enzyme systems (16 loci) yielded interpretable results for all populations. A high differentiation was encountered for the Western Atlantic A. bermudensis population (F_ST=0.434), partially due to the presence of a diagnostic locus (LAP) between Bermuda and Brazilian populations. This result could be taken as an indication that the Brazilian population should be elevated to a specific status. We do expect some genetic differentiation, however, between natural populations separated over wide geographic distances. Finally, since Mantel and regression analyses did not rule out the isolation by distance model, we have conservatively decided to maintain the specific status of A. bermudensis from Brazil.     

Sex steroid levels,oocyte maturation and spawning performance in Waigieu seaperch (Psammoperca waigiensis) exposed to thyroxin,human chorionic gonadotropin,luteinizing hormone releasing hormone and carp pituitary extract

In the present study, we have investigated the sex steroid hormone levels, oocyte maturation and spawning performance in Waigieu seaperch (Psammoperca waigiensis) exposed to different doses (0, (control), 0.05, 0.25 and 0.5 mg/kg fish) of thyroxin (T₄) both through diet (continuously) and injection (single injection). In addition, we also studied plasma steroid hormone levels and spawning performances in female fish injected with a single dose of D-Ala⁶, Pro⁹-Net-mGnRH (LHRHa: 50 µg/kg), human chronic gonadotropin (HCG: 1,500 IU/kg) and carp pituitary extract (CPE: 10 mg/kg). In all experiments, samples were collected at 0, 6, 12, 24 and 48 h after exposure. T4 exposure via dietary route produced differential and enhanced effects, compared with when the compound was injected to the broodstock. A significant association between exposure to dietary T4, elevated plasma steroid hormone levels, maturation-, spawning-, fertilization- and hatching rate, egg diameter, embryogenesis and larval growth were observed. Interestingly, we observed that broodstock groups fed with T4 doses spawned 20 days earlier than the control group. Thus, we propose that these differences may be attributed to higher systemic availability of T4 due to dietary exposure that is easily transferable to eggs and embryos, as opposed to injection that require absorption to increase bioavailability. Furthermore, our results show that LHRHa, CPE and HCG produced significant increase in spawning rate, but significantly reduced fertilization- and hatching rates. Waigieu seaperch is a new candidate for marine aquaculture in Vietnam and relatively little is known about the reproductive biology and endocrinology of this species. Therefore, the present study forms an integral basis for understanding the reproductive endocrinology of a tropical marine finfish with increasing aquaculture prospects and may also contribute in the development of sustainable aquaculture of this species in a developing country such as Vietnam.     

Quantitative studies on the reproduction of black scallop,Chlamys varia (L.) from lanveoc area (Bay of Brest)

The values of gonad index calculated by the allometric relationships of dry gonad weight over dry body weight of the black scallop, Chlamys varia (L.), gave peak values for May and September during 1976 and 1977. Histological studies on gonads from natural populations and periodic biopsies of gonads from marked animals in experimental cages showed that, in addition to intermittent spawnings between May and September, two peak spawning periods were noteworthy. These were a partial spawning in May–June and a complete spawning in September–October. The energy spent as gametes for these two spawnings has been calculated for individual males and females in each age group of the population and the cost of spawning by the whole population has been estimated. The population spent more energy for spawning in 1977 (144.49 kcal/100 m²) than in 1976 (83.70 kcal/100 m²) and the reproductive effort of an average adult was 0.04 in 1976 and 0.10 in 1977.     

Thermohaline tolerance and embryonic development in capelin eggs (Mallotus villosus) from the Northeast Atlantic Ocean

Capelin (Mallotus villosus) displays alternative reproductive modes throughout its circumpolar distribution. This predicts divergent thermohaline tolerance of eggs because they are incubated in either a steady offshore or variable intertidal environment. We investigate herein thermohaline tolerance of eggs from the offshore spawning Barents Sea capelin. Subsequently, we compare our data with those previously published on other offshore and intertidal spawning capelin populations across the Northeast Atlantic Ocean, with the aim of determining possible patterns in the thermohaline tolerance of eggs from the alternative reproductive modes. In a 2?×?4 factorial design various combinations of salinities and temperatures had only negligible effect on the survival of eggs until first hatch. The embryonic development rate from fertilisation until first hatch across populations and between the two reproductive modes suggested non-local thermohaline tolerance towards the physical factors during development. Finally, no differences were observed in salinity tolerance from fertilisation to first hatch between populations representing different reproductive modes. The present findings demonstrate wide thermohaline tolerance of capelin eggs regardless of population origin and reproductive mode.     

Coral spawning in the western Pacific Ocean is related to solar insolation: evidence of multiple spawning events in Palau

Coral reproductive schedules have long been related to concomitant increases in regional sea surface temperature (SST). Yet, corals also mass spawn in the tropics, where SSTs vary little throughout the year. Here we show that the rise toward and fall from solar insolation maxima, which is the electromagnetic energy incident on the surface of the earth, coincide with coral spawning events in tropical Palau. Two insolation maxima (a consequence of the vernal and autumnal equinoxes) in the tropics lead to multiple spawning events per year. SSTs are poor predictors of coral spawning in the tropics. Multiple spawning events increase the rate of genetic recombination, which in turn may facilitate the likelihood of speciation and explain, in part, the high coral diversity in the tropics. We also show that mass spawning coincides with near-maximum solar insolation (5.0–7.2 kWh/m²/day) events from 33°N to 30°S in the western Pacific Ocean, and should be considered as one of the primary variables driving coral reproductive cycles.     

The genetic structure of populations of the sea urchin Strongylocentrotus intermedius from the northwestern Sea of Japan in connection with a shift in spawning time

Usin seven allozyme loci as gene markers, we studied the genetic structure of ten natural populations of the sea urchin Strongylocentrotus intermedius in the northwestern Sea of Japan that differ in the proportion of individuals with different spawning seasonality (early spawning at the end of May?CJune and late spawning in September-early October). This study revealed the spatial genetic heterogeneity of the sea-urchin populations (F _st = 0.051); its degree was independent of the geographic distance between populations. Out of the seven loci that were surveyed, four loci (peptidase Pep-1, Pep-2, mannose phosphate isomerase Mpi, and inorganic pyrophosphatase Ipp) accounted for the differences between pairs of samples; different loci contributed to the variation in each sample pair. The genetic similarity between pairs of populations ranged from 0.905 to 0.988. The genetic heterogeneity of the sea-urchin populations seems to be a result of both genetic drift and natural selection. At the same time, no significant genetic differences were found between specimens of S. intermedius with different spawning times (the genetic similarity was 0.988?C0.991). The shift in spawning season from autumn to early summer in the populations of S. intermedius inhabiting the areas of Peter the Great Bay adjacent to Vladivostok city can be explained by a phenotypic response of this species to environmental changes caused by chronic anthropogenic pollution of the bay.     

The Importance of Coral Larval Recruitment for the Recovery of Reefs Impacted by Cyclone Yasi in the Central Great Barrier Reef

Cyclone Yasi, one of the most severe tropical storms on record, crossed the central Great Barrier Reef (GBR) in February 2011, bringing wind speeds of up to 285 km hr⁻¹ and wave heights of at least 10 m, and causing massive destruction to exposed reefs in the Palm Island Group. Following the cyclone, mean (± S.E.) hard coral cover ranged from just 2.1 (0.2) % to 5.3 (0.4) % on exposed reefs and no reproductively mature colonies of any species of Acropora remained. Although no fragments of Acropora were found at impacted exposed sites following the cyclone, small juvenile colonies of Acropora (<10 cm diameter) were present, suggesting that their small size and compact morphologies enabled them to survive the cyclone. By contrast, sheltered reefs appeared to be unaffected by the cyclone. Mean (± S.E.) hard coral cover ranged from 18.2 (2.4) % to 30.0 (1.0) % and a large proportion of colonies of Acropora were reproductively mature. Macroalgae accounted for 8 to 16% of benthic cover at exposed sites impacted by cyclone Yasi but were absent at sheltered sites. Mean (± S.E.) recruitment of acroporids to settlement tiles declined from 25.3 (4.8) recruits tile⁻¹ in the pre-cyclone spawning event (2010) to 15.4 (2.2) recruits tile⁻¹ in the first post-cyclone spawning event (2011). Yet, post-cyclone recruitment did not differ between exposed (15.2±2.1 S.E.) and sheltered sites (15.6±2.2 S.E.), despite the loss of reproductive colonies at the exposed sites, indicating larval input from external sources. Spatial variation in impacts, the survival of small colonies, and larval replenishment to impacted reefs suggest that populations of Acropora have the potential to recover from this severe disturbance, provided that the Palm Islands are not impacted by acute disturbances or suffer additional chronic stressors in the near future.     

Neighboring Deschampsia flexuosa and Trientalis europaea harbor contrasting root fungal endophytic communities

Fungal endophytic communities and potential host preference of root-inhabiting fungi of boreal forest understory plants are poorly known. The objective of this study was to find out whether two neighboring plant species, Deschampsia flexuosa (Poaceae) and Trientalis europaea (Primulaceae), share similar root fungal endophytic communities and whether the communities differ between two sites. The study was carried out by analysis of pure culture isolates and root fungal colonization percentages. A total of 84 isolates from D. flexuosa and 27 isolates from T. europaea were obtained. The roots of D. flexuosa harbored 16 different isolate types based on macromorphological characteristics, whereas only 4 isolate types were found in T. europaea. The root colonization by dark septate and hyaline septate hyphae correlated with isolate numbers being higher in D. flexuosa compared to T. europaea. The different isolate types were further identified on the basis of internal transcribed spacer sequence and phylogenetic analysis. An isolate type identified as dark septate endophyte Phialocephala fortinii colonized 50 % of the T. europaea and 21 % of the D. flexuosa specimens. In addition, Meliniomyces variabilis, Phialocephala sphaeroides, and Umbelopsis isabellina were found colonizing the grass, D. flexuosa, for the first time and Mycena sp. was confirmed as an endophyte of D. flexuosa. Site-specific differences were observed in the abundance and diversity of endophytic fungi in the roots of both study plants, but the differences were not as predominant as those between plant species. It is concluded that D. flexuosa harbors both higher amount and more diverse community of endophytic fungi in its roots compared to T. europaea.     

Temporal and Spatial Occurrence of Female Chinook Salmon Carrying a Male-Specific Genetic Marker in the Columbia River Watershed

Recent declines in many chinook salmon, Oncorhynchus tshawytscha, populations within the Columbia River watershed have prompted an examination of their reproductive biology. In a previous study many female fall chinook salmon collected in 1999 from the Hanford Reach of the Columbia River tested positive for a male-specific DNA marker (OtY1) found on the Y chromosome. The purpose of this study was to determine if females testing positive for the OtY1 marker could be found in other populations of fall chinook salmon from the Columbia River, and to assess the prevalence of OtY1 incidence in different female cohorts. Post-spawned male and female fall chinook salmon from three different naturally spawning populations (Hanford Reach, Yakima River and Ives Island) and one hatchery population (Priest Rapids Hatchery) on the Columbia River were tested in 2000 and 2001 for the OtY1 marker. Among naturally spawning populations, 57.4% of the females tested positive from the Hanford Reach, 33.3% tested positive from the Yakima River, and 32.5% tested positive from Ives Island. Of the Priest Rapids Hatchery fish, 62.5% of the females tested positive, and significant differences were detected between the 1995–1996 and 1997–1998 female cohorts from this population. No significant differences were detected between any of the female cohorts from the naturally spawning populations. All male chinook salmon samples, tested positive for OtY1.     

Population structure, recruitment, and succession of the brown alga, Padina boryana Thivy (Dictyotales, Heterokontophyta), at an exposed shore of Sirinart National Park and a sheltered area of Tang Khen Bay, Phuket Province, Thailand

The brown algal genus, Padina, has a worldwide distribution in tropical and subtropical climate zones. Padina individuals are common and sometimes dominant in both the intertidal and shallow subtidal regions associated with coral reefs. We investigated the population structure and recruitment of two populations of Padina boryana at an exposed shore in Sirinart National Park (SNP) and a sheltered shore of Tang Khen Bay (TKB), Phuket Province, Thailand. From September 2005 to August 2006, the number of released spores and the height and radius of fronds were measured monthly. New recruits were recorded and monitored on manipulated permanent plots 0.25 m². The experiment was carried out monthly over a year. We found Padina recruits 1 month after the plots were cleared at both sites. There was a significant difference in percentage cover by new individuals between the two locations (P < 0.05) and also at the shore levels within the sites. At SNP, the highest recruitment was found in the uppermost zone, while at TKB high recruitment occurred at all shore levels except at 80-100 m from the shore. The factors influencing recruitment of P. boryana include wave motion, competition with other earlier successional species and sediment. The high availability of reproductive spores throughout the year, the successful recruitment and the Dictyerpa stage promote the successful establishment of Padina populations.     

Divergence in reproductive ecology of the three-spined stickleback,Gasterosteus aculeatus

An anadromous population (trachurus form) and three freshwater populations (leiurus form) of the three-spined stickleback,Gasterosteus aculeatus, in central Japan were compared with one another in the reproductive traits: body length at maturity, egg size, clutch size, the swell of abdomen and the number of eggs per nest. The anadromous fish which become larger in body size at maturity spawn eggs smaller in size and greater in number than the freshwater fish. The abdomen swell of gravid females expressed by the proportion of abdomen width to body length was greater in the freshwater fish. The anadromous male fish collected a mean of 2,638 eggs with a range of 1,119 to 4,052 eggs from about 6–7 females. In the three freshwater (the Yamayoke, the Tsuya and the Jizo) populations, males must have mated with about 9–22, 7–18 and 4–7 females respectively. It seems that theleiurus form increases its reproductive success by its much more mating opportunities and the parental efforts of nesting males as well as by spawning large eggs. Furthermore, among the freshwater populations, the Jizo one inhabiting the upper stream was clearly larger in body size, in egg size and in clutch size than the Yamayoke and the Tsuya ones which inhabit stable waterbodies with springs. It is possible that the Jizo population adopted the strategy of spawning a few large eggs as an adaptation to its habitat. The causal and functional explanations in reproductive characteristics among the four populations are discussed in regard to differences in the environmental conditions.