Early Spawning Research Articles

The climate‐induced changes in the life history of the common cuttlefish in the English Channel

AbstractThe population of common cuttlefish Sepia officinalis in the English Channel recently developed two life cycles: annual (spawning 1 y.o.) and biennial (spawning 2 y.o.) instead of the biennial strategy known before, associated with increasing environmental temperatures in recent decades because of climate changes. Both groups differ in the size of mature animals (110–196 mm mantle length vs. 140–262 mm) and the number of chambers in the cuttlebone (60–97 in annual vs. 93–152 in biennial). The annual group represented some 15%–20% of the population, and the proportion of early spawners increased during the reproductive period, from 3%–5% in February/March to 50%–70% in June/July. Among spawning cuttlefish males predominated as ~2:1. Such environmentally driven changes in historical ecology as exemplified by the cuttlefish might be a critical link in the adaptation of the cephalopod life cycles to changing ecosystems.

An update on the biological parameters of the Norway lobster (Nephrops norvegicus) in the northwestern Mediterranean Sea

Abstract The Norway lobster, Nephrops norvegicus, is one of the most valuable fishery resources in many coastal countries of the Mediterranean Sea and the northeastern Atlantic Ocean. In the Mediterranean Sea, several stocks are being overexploited, with ecological, economic, and social consequences. To perform an adequate stock assessment and provide guidance on maximum sustainable yield, reliable biological parameters of the species are required. Considering that biological parameters may change over time in overexploited populations, in the present study, we updated key biological parameters for the N. norvegicus stock of the northwestern Mediterranean Sea: size at which 50% (L50) of females were in reproductive condition, length–weight relationship, and individual size structure. Moreover, daily landings were combined with the spatial position of the vessels tracked by their Vessel Monitoring System (VMS), to obtain information on the geographical distribution and time series of Landings Per Unit Effort (LPUE), as well as total landings from 2008 to 2021. Our results suggest overexploitation of the resource, revealing a severe reduction in size at 50% maturity, an earlier spawning and brooding period, and a clear decrease of LPUE over time.

Will most suitable spawning grounds for coastal fishes be impacted by climate change? A larval drift modelling approach

For many fishes, their early life stages are transported (passively) by currents between spawning areas and coastal nurseries, but also potential dispersal towards new habitats. Therefore, species have developed strategies to enhance the recruitment success, including the selection of appropriate spawning grounds. However, increased temperature due to climate change may lead to changes in hydrodynamics, shorter larval drifts, and earlier spawning, and consequently the location of the most suitable spawning grounds may change. We investigated whether the location of the most favourable spawning areas (allowing higher rates of larvae reaching coastal nurseries) was stable over time, and if differences could be found between environmentally contrasted years. We used a larval drift model taking into account hydrodynamics, larval characteristics and behaviour for three commercially exploited fish species (sole Solea solea, flounder Platichthys flesus and seabass Dicentrarchus labrax) in the Western Europe (encompassing the Bay of Biscay, the Celtic Sea and the English Channel). According to our model, we conclude that despite contrasting environmental conditions, the location of spawning grounds allowing the best chance of recruitment to nurseries for the offspring was fairly similar. However, even if the location of the main spawning grounds is stable over time, their relative effectiveness varies greatly between years. This would suggest that natural selection may favour the emergence of homing behaviour. This stability in this fish essential habitat location could facilitate protection measures. Going further, it could be interesting to study the variations occurring in spawning grounds (in terms of recruitment success, and retention/dispersion) during the course of a spawning season.

The development of gonads in females of the common perch Perca fluviatilis from the lower Dnister in the vegetative period

The present paper presents the scientific results regarding the particularities of the oogenesis of the common perch in the lower sector of the Dniester river. In the mentioned species, the development of the oocytes is synchronous, which determines a unitary mode of spawning. Differences in the character of oocyte development were established in breeders of different sizes, indicating earlier spawning by breeders of perch in smaller gravimetric groups. In sevenyearold females with ovaries in developmental stages II and II-III, resorption of oocytes was found in the phase of protoplasmic growth and in the initial phases of vacuolation of the cytoplasm, which indicates the attenuation of reproductive function in higher age groups. In May, an individual hermaphrodite perch with an abnormal development of germ cells was captured.

Reproductive Aspects of the Bamboo Clam Solen lamarckii (Dhayes 1839), in Bengkalis Island Waters, Indonesia.

<b>Background and Objective:</b> Bamboo clam <i>Solen lamarckii</i> is one of the bivalve's species that have important economic value in Indonesian waters. Knowledge of the reproductive biology of a species is essential for proper and sustainable fisheries management. Monthly variations in the gonad maturity level of the clams from the coastal waters of Bengkalis Island Indonesia, were examined. <b>Materials and Methods:</b> Samples of the clam were collected monthly at the intertidal zone during low tide from May to September, 2020. A total of 239 specimens of which 116 females and 123 males were examined. Reproductive aspects observed in this study included sex ratio, gonadosomatic index, monthly gonadal maturity level and female fecundity. Mature female or near spawning phases were used for fecundity estimation. The sex ratios were analysed using a Chi-quadrat-Test, whereas to determine differences in fecundity between female individuals tested by Analysis of Variance. <b>Results:</b> Based on the gonadosomatic index (GSI) and histological observation of both sexes's gonads, it can be concluded that early spawning occurred in August and the peak seemed to take place during October-November. The sex ratios were analysed using a Chi-quadrat-Test which was not different from parity. Gonad maturation time between males and females indicates synchrony and no hermaphrodites were observed in the collection. Females shell length range of 75.5 to 89.3 mm produced 4.63×103-7.43×103 eggs ind-1 female (N = 10). Females with a shell length between 75.5 and 89.3 mm had varying fecundities, but analysis of variance showed no significant difference (Sig>0.05). <b>Conclusion:</b> Based on the gonadosomatic index (GSI) and histological analysis, <i>S. lamarckii</i> in Bengkalis waters spawned in August. Males and females showed spawning synchrony.

Dynamics of the size and age composition of the arabesque greenling Pleurogrammus azonus in the pelagial of the russian waters in the sea of Japan

In the pelagial of the Russian waters of the Sea of Japan, juveniles and adults of the Arabesque greenling Pleurogrammus azonus are found from March to November. The average size of fingerlings of Arabesque greenling increase from South to North. Larger sizes of fingerlings in the north are determined by earlier spawning, compared to the south. Density aggregations of Arabesque greenling in the pelagic zone is much smaller than in the bottom layers of water. High migration activity is characteristic of a smaller hart of individuals.

The effects of spatial and temporal variations in spawning on offspring survival in Northeast Arctic cod

Abstract Climate change and harvesting result in temporal and spatial changes and variability in spawning, and thus in offspring ambient drift conditions. As a result, variable survival of offspring and thereby in recruitment are expected. This is especially true for species with long reproduction migration as is the case for some Atlantic cod stocks. We utilize biophysical model simulations to analyze survival from spawning until age 1 resulting from different scenarios of spatial and temporal changes in spawning. We find that survival is 1.5–2 times higher when spawning is shifted southwards as compared to northerly shifts. In general, survival is more sensitive to shifts in spawning location than in spawning time. Early spawning is only favourable if spawning is concurrently shifted farther north. A future spawning scenario with a northward shift in spawning grounds beyond what has been observed historically suggests reduced offspring survival and increased sensitivity to the timing of spawning.

Influence of Thermal Regimes on the Relationship between Parasitic Load and Body Condition in European Sardine along the Catalan Coast

The small pelagic European sardine presents high commercial and ecological values. Due to its cold-temperate water affinity, stocks are affected by global warming. Water temperature rise may change primary productivity patterns, negatively affecting fish condition and increasing parasite incidence. In this context, sardine health status was evaluated through the annual cycle on the Catalan Coast using thermal regimes comparison. Morphogravimetric parameters, sex and gonadal stages were assessed; infection by nematodes was characterised, and body condition was estimated by the Le Cren Factor and lipid content measured using a fish fat meter. Significant statistical differences were observed in spawning dynamics, body condition, and parasite infection between thermal regimes. Sardines from the colder north area had better condition and an earlier spawning, with lower parasite incidence (in terms of total prevalence, mean intensity and abundance) than those from the southern coast. Hysterothylacium spp. was the most abundant nematode, while Anisakis spp. prevalence was null in the two locations. Seasonal differences in nematode load were observed along the Catalan Coast, with lower prevalence during the summer and higher in winter-spring. Although previous studies have underestimated parasite influence on sardine health status, parasite abundance and sardine condition were negatively correlated. Seawater temperature and primary productivity are the proposed factors promoting differentiation in nematode infection and fish condition throughout the annual cycle and between locations.

Disentangling seasonal from maternal effects on egg characteristics in western Baltic spring-spawning herring Clupea harengus.

In marine fishes, the timing of spawning determines the environment offspring will face and, therefore, the chances of early life stage survival. Different waves of Atlantic herring Clupea harengus spawn throughout spring in the western Baltic Sea, and the survival of offspring from early in the season has been low in the most recent decade. The authors assessed changes in egg traits from early, middle and late phases of the spawning season to examine whether seasonal and/or maternal effects influenced embryo survival. At each phase, fertilized eggs of six to eight females were incubated at two temperatures (7 and 13°C), and egg size, fertilization success, mortality and time to hatch were recorded. A compilation of data from 2017 to 2020 spawning seasons indicated that mean total length of females decreased with progression of the season and increasing in situ water temperature. For the sub-set of females used in the laboratory study, early spawners were 7.6% larger and produced 14.2% larger eggs than late-spring spawners. Fertilization success was consistently high (>90%), and mortality to hatch was low (<3%). Neither the former nor latter were influenced by season, but both were influenced by maternity. This significant female effect was, however, not related to any maternal trait measured here (total length, Fulton's condition factor or age). There was no maternal effect on development rate at 7 or 13°C. The results suggest that intrinsic differences among females or among spawning waves are unlikely to markedly contribute to the poor survival observed for progeny from early in the season in this population and point towards other extrinsic factors or processes acting on eggs or early larval stages (e.g., seasonal match-mismatch dynamics with prey) as more likely causes of mortality.

Earlier or delayed seasonal broodstock spawning changes nutritional status and metabolic programming of growth for next-generation Atlantic salmon

Atlantic salmon (Salmo salar) breeding companies depend on changing light, temperature and feeding regimes to achieve new generations outside the natural spawning season. However, there have been few conducted trials reported that have studied whether this shift affects important traits. We test whether an induced shift of two months earlier or two months later than normal spawning season affects the nutritional status (folate, methionine, vitamin B12, vitamin B6, free amino acids, N-metabolites and lipids) in broodstock liver and muscle and whether this affects the levels of the same nutrients in the offspring. The results showed significant seasonal differences in the Cahill cycle (glucose-alanine cycle), 1C metabolism and for free amino acids catabolized in the citric acid cycle all which are important for embryonic growth The broodstock nutritional status was reflected in the eggs. Nutritional status of broodstock liver and muscle and newly fertilized eggs showed two general scenarios: Advanced spawning period did not obtain optimal deposition of nutrients in the eggs. Delayed spawning broodstock displayed a metabolic profile which indicated that it had enhanced catabolization of muscle protein which led to accumulation of aminogroups from muscle breakdown to such a degree that these amino groups were increased in the eggs. The total body weight at start-feeding stage revealed best growth for both the normal and late spawning compared to early spawning. We show here that environmental alterations in broodstock husbandry influence the nutrient status of the next generation via nutritional and metabolic programming. This is an important concept which needs more careful awareness as the metabolism compensate and regulate the energy between catabolism and anabolism through the early stages of cell divisions which give rise to changes in permanent traits for the next generation.

Asymmetric competition over space use and territory between native brown trout (Salmo trutta) and invasive brook trout (Salvelinus fontinalis).

Interference competition over food and territory can shape population structure and habitat use within and between species. The introduction of invasive species often leads to novel competitive interactions over shared resources and invaders can eventually exclude the native species from preferred habitats. Invasive brook trout (Salvelinus fontinalis) introduced to northern Europe have excluded native brown trout (Salmo trutta) from numerous headwater streams. The fact that invasive brook trout can displace the more aggressive brown trout is puzzling. However, the earlier spawning and hatching of brook trout, compared to brown trout, may lead to unequal competition due to size advantage and prior resident status of brook trout at the fry stage. In this study, we examine the effect of competition between brown trout and brook trout using the natural size distribution of the two species. In two consecutive experiments, we first measured space use and feeding of a fry (age 0+) in the presence of a juvenile (age 1+). In experiment 2, we assessed territorial interactions between the species at the fry stage (age 0+) and if smaller brown trout could compensate the disadvantage by manipulating residence duration. Fry of brook trout feed sooner and spend more time close to the larger individual than brown trout fry. We also found that brook trout fry won most territorial contests against brown trout, and that increased residence duration led to longer and more aggressive interactions. The results suggest that smaller brown trout are displaced to suboptimal habitats in the presence of a larger brook trout. Therefore, the later emergence from gravel beds resulting in the naturally occurring size disadvantage of brown trout at the fry stage may lead to unequal territorial interactions that could explain why brown trout are displaced from preferred habitats in sympatry with brook trout.

Intra- and inter-annual shifts in foraging tactics by parental northern gannets Morus bassanus indicate changing prey fields

Seabirds are constrained by central-place foraging during breeding, when the energy obtained from prey must outweigh the costs of travel, search, capture and transport. The distribution and phenology of the cold-blooded marine fishes they exploit are heavily influenced by oceanic climate. Northern gannets, the largest breeding seabird in the North Atlantic, use a generalist foraging strategy, preying on a wide array of pelagic fishes. They employ different foraging tactics for different prey types, with rapid, shallow V-shaped dives used for large, powerful prey such as mackerel, and U-shaped dives for smaller forage fishes like capelin. Here we assess intra- and inter-annual differences in foraging effort and influences of prey availability at the southernmost colony of the species at Cape St. Mary’s, Newfoundland, Canada. We compared foraging trip characteristics (total and maximum distance, directness, duration and number of dives) of parental gannets during the breeding seasons of 2019 (n = 10) and 2020 (n = 7) using GPS/time-depth recorders. Individual gannets shifted away from using U-shaped dives in early chick-rearing to primarily V-shaped dives in late chick-rearing. Shifts were abrupt and occurred in mid-August in 2019 and 2020. Maximum and total foraging trip distance and duration were significantly greater during early chick-rearing in 2020 than in 2019. Kernel density 50% utilization distributions were larger and expanded further from the colony during early chick-rearing in 2020 (7297 ± 1419 km2; mean ± SE) than 2019 (2382 ±797 km2). Increased foraging effort during early chick-rearing in 2020 was likely due to decreased capelin availability, resulting from earlier spawning, and greater variation in the timing of spawning among sites, which may have been influenced by warmer waters.

Early life growth is affecting timing of spawning in the semelparous Barents Sea capelin (Mallotus villosus)

Capelin (Mallotus villosus) is a forage fish and a key species in the Barents Sea (BS). The BS capelin are semelparous and hence only spawn once along the north coasts of Norway and Russia before they die. The age at spawning ranges from 2 to 5 years and the spawning season peaks in March/April but starts in February and lasts until June, and the causes of the variability in timing of spawning are not well understood. Here, we aimed to find out whether early growth is associated with the timing of spawning in BS capelin, both on the individual and population level, and if there is an association between early life growth and the spatial distribution at the nursery areas and feeding grounds. For the analysis, we used an extensive dataset comprising >150000 otolith growth zone measurements carried out during surveys from 1976 to 2019 both from the spawning and feeding areas. The data from the feeding area showed that capelin with good first-year growth were found in the productive north-west part of the Barents Sea at both age 1 and 2, while capelin with relatively poor first-year growth were typically found in the south-east Barents Sea. The data from the spawning area showed on the individual level that capelin with good first-year growth tend to spawn both at a younger age and earlier in the season. The capelin spawning late in the season were also generally smaller than early spawners. On the population level, a contradictory pattern was observed where the proportion of maturing capelin at age 2 and 3 was negatively correlated with first-year growth indicating that the great variability in year-class strength masks the general effect found at the level of individual fish. Furthermore, first-year growth was positively associated with the abundance of 1-year-old capelin indicating that rapid growth early in life enhances recruitment. On the other hand, first-year growth was strongly negatively correlated with third-year growth suggesting an increased effect of density-dependent growth with age and/or compensatory growth, or reduced growth linked to earlier maturation. In sum, our results show that the first-year growth affects growth, maturation processes, and timing of spawning later in life, thus potentially strongly influencing capelin population dynamics.

From spawning to first-year recruitment: the fate of juvenile sole growth and survival under future climate conditions in the North Sea

Abstract This study shows the effect of climate change on the growth and survival of early life history stages of common sole (Solea solea) in different nursery areas of the North Sea, by combining a larval transport model with an individual-based growth model (Dynamic Energy Budget) to assess the fate from egg to young of the year at the end of the first growth season. Three scenarios of climate change, inspired by the 2040 Intergovernmental Panel on Climate Change projections, are tested and results are compared to a reference situation representative of current climate conditions. Under climate change scenarios where wind changes, water temperature increases and earlier spawning are considered, the early arrival of fish larvae in their nurseries results in larger young of the year at the end of summer. However, early arrival leads to higher mortality due to initially slow growth in spring. Future climate scenarios result in higher biomass and reduced first-year survival. How this result translates into changes at population level and stock management needs further investigation. Nonetheless, this study illustrates that processes linking life stages are paramount to understand and predict possible consequences of future climate conditions on population dynamics.

Itsas ingurumenerako mikrokutsatzaile organiko hidrofobikoen presentzia eta eraginak aztertzeko estrategien taxutzea

Lan honetan, ingurumen analisirako metodologia planteamendu berri bat proposatu da. Horretarako, kimikariek eta biologoek baldintza kontrolatuetako esposizioa egiteko elkarlanean jardun genuen. Esperimentu honetan, muskuiluak eta lagin-biltze pasiboko tresnak hainbat mikrokutsatzaile hidrofoboren eraginpean jarri ziren. Batetik, kutsatzaileen kontzentrazioak neurtu ziren, lagin-biltze puntualen zein lagin-biltze pasiboen bitartez. Bestetik, muskuiluetan kutsatzaileen kontzentrazioak neurtu ziren. Biologoek, euren aldetik, muskuiluen azterketa histopatologikoa egin zuten. Azkenik, NMR-n oinarritutako metabolomika erabili zen muskuiluek kutsatzaileen aurrean ematen zuten erantzuna aztertzeko. Lau estrategien konbinazioarekin, kausa (kokteleko mikrokutsatzaileen kontzentrazioak eta muskuiluek metatutakoa) eta eragindako efektuak (histologia azterketetan behatutakoak) hobeto uler ditzakegu. kutsatzaileek eragiten dituzten aldaketak ulertzeko eta ondorioak azaltzeko metabolomika baliabide erabilgarria dela ondorioztatu genuen. kutsatzaileen koktelak errute goiztiarra eragin zien muskuiluei; izan ere, NMR metabolomika erabiliz, aldaketa metaboliko nabarienak errute-egunean ikusi ziren.

Влияние экологических факторов на ранний онтогенез и численность пиленгаса Planiliza haematocheila в Азовском море

In the article, an analysis of so-iuy mullet (Planiliza haematocheila) natural&#x0D; reproduction conditions was performed in the Sea of Azov over the past 17 years.&#x0D; The optimal and critical temperatures and salinity of the water were determined&#x0D; for the effective spawning of so-iuy mullet as well as the influence of these factors&#x0D; on its early ontogenesis, the dependence of the migration periods and spawning&#x0D; of producers. An earlier spawning was observed in estuaries and bays.

Otolith oxygen isotope analysis and temperature history in early life stages of the chub mackerel Scomber japonicus in the Kuroshio–Oyashio transition region

To determine the temperature history of early life stages of chub mackerel (Scomber japonicus), otolith stable oxygen isotope ratios (δ18Ootolith) of larval and juvenile fish collected in the Kuroshio–Oyashio transition area during 2004–2015 were analyzed, and experienced temperatures were estimated accordingly. The δ18Ootolith values decreased with otolith growth during the larval stage, whereas those for juveniles were positively correlated with otolith radius and increased with increasing otolith size. Combinations of δ18Ootolith values, average otolith daily increment width, and daily age were representative of the differences between better and poorer recruitment years, the former being characterized by earlier spawning and faster growth (resulting from cooler experienced temperatures), and the latter by slower growth. Analyzed fish were sorted into larval and early juvenile growth stages by cluster analysis; the high-growth cluster exhibited higher δ18Ootolith values than the low-growth cluster. The conversion of δ18Ootolith values to water temperature indicated that the higher growth cluster experienced a water temperature ca. 2.0 °C cooler during the later juvenile stage. Therefore, our results suggest the presence of a growth positive spiral, wherein individuals with high initial growth proactively enter cooler water temperature areas, accessing a highly nutritious diet resulting in further rapid growth.

EXPERIMENTAL ANALYSIS OF MODERN STATE OF REPRODUCTION FOR CHERRY SALMON ONCORHYNCHUS MASOU AT THE FISH FARMS OF SAKHALIN REGION

Growing of cherry salmon juveniles under two different temperature regimes at the salmon farms Anivsky and Okhotsky in the fish-rearing cycle of 2016–2017 is analyzed. Data on cherry salmon growing for other fish farms of Sakhalin region collected in 1995–2017 are considered, as well. The periods of fish feeding and dynamics of their growth varied significantly in dependence on temperature conditions. The feeding started in April-May at the cold-water fish farms (Anivsky, Lesnoy, Sokolovsky, Urozhainiy) where the water temperature lowered in winter to 0.2–0.3 о С, but in February at Reidovo fish farm where the water temperature were not lower than 2 о С and in January at the most warm-water Okhotsky fish farm with the temperature never lower than 6.5 о С. In accordance with growing conditions, the growth rate of juveniles was high in winter month at the warm-water fish farms, where the ground water was used for rearing, but increased since May-June at the cold-water fish farms using natural heating of the river water. However, several cases were noted when the fish that accumulated less than 500–700 degree-days released from cold-water fish farms in June-July were larger than those from warm-water fish farms. Thus, cherry salmon is the only species among pacific salmons whose juveniles can be successfully grown at any temperature regime and consequently at any fish farm. This ability is reasoned by earlier spawning (along with pink salmon) and long period of development in rivers. At cold-water fish farms, the best results for cherry salmon growing could be achieved with the eggs planting in late August-September, whereas the time of eggs planting is not significant for warm-water fish farms.

Artificial selection on reproductive timing in hatchery salmon drives a phenological shift and potential maladaptation to climate change.

The timing of breeding migration and reproduction links generations and substantially influences individual fitness. In salmonid fishes, such phenological events (seasonal return to freshwater and spawning) vary among populations but are consistent among years, indicating local adaptation in these traits to prevailing environmental conditions. Changing reproductive phenology has been observed in many populations of Atlantic and Pacific salmon and is sometimes attributed to adaptive responses to climate change. The sockeye salmon spawning in the Cedar River near Seattle, Washington, USA, have displayed dramatic changes in spawning timing over the past 50 years, trending later through the early 1990s, and becoming earlier since then. We explored the patterns and drivers of these changes using generalized linear models and mathematical simulations to identify possible environmental correlates of the changes, and test the alternative hypothesis that hatchery propagation caused inadvertent selection on timing. The trend toward later spawning prior to 1993 was partially explained by environmental changes, but the rapid advance in spawning since was not. Instead, since its initiation in 1991, the hatchery has, on average, selected for earlier spawning, and, depending on trait heritability, could have advanced spawning by 1–3 weeks over this period. We estimated heritability of spawning date to be high (h 2 ~0.8; 95% CI: 0.5–1.1), so the upper end of this range is not improbable, though at lower heritabilities a smaller effect would be expected. The lower reproductive success of early spawners and relatively low survival of early emerging juveniles observed in recent years suggest that artificial and natural selection are acting in opposite directions. The fitness costs of early spawning may be exacerbated by future warming; thus, the artificially advanced phenology could reduce the population’s productivity. Such artificial selection is known in many salmon hatcheries, so there are broad consequences for the productivity of wild populations comingled with hatchery‐produced fish.

REPRODUCTIVE BIOLOGY OF THE FRESHWATER MUSSEL, NITIA TERETIUSCULA (PHILIPPI, 1847) (BIVALVIA: UNIONIDAE) FROM THE NILE RIVER IN EGYPT

Seasonal reproductive cycle, gonad structure, gametogenesis, larval development and sex ratio of the freshwater mussel, Nitia teretiuscula (Philippi, 1847) was investigated for the first time. A total of 200 mussels, were randomly collected each month from September 2016 to August 2017 from four regions along Nile River, Egypt: El-Kanater (Qaluobiya Governorate), Tura (Helwan Governorate) Geziret Bein El-Bahrein (Giza Governorate) and Geziret El-Dahab (Cairo Governorate). Histological examination of the gonads showed that N. teretiuscula is a dioecious species with a 1:1 sex ratio. The female and male gonads were found to be paired and asymmetrical organs, situated between the mantle and digestive gland. Female follicles contain edoogonia and oocytes that could be separated into, previtelogenin, vitelogenin and postvitelogenin stages. Male follicles contained spermatogonia and spermatocytes that could be classified as primary spermatocytes, secondary spermatocytes and spermatids. Moreover, the reproductive cycle of both sexes included four developmental stages, developing, ripened (mature), spawning and spent. The predominant stages were ripening (mature) and spawning, whereas spent gonads were rare. Gametogenesis began in early spring and spawning occurred in late spring. Although mature oocytes and spermatozoa were present for almost the entire year, gonadal activity seemed lowest in autumn months. Both sexes displayed the most gonadal activity during the winter months. Consequently, eggs and larval stages (glochidia) were incubated for a short period within both the outer and inner demibranchsso; N. teretiuscula can be considered atetragenic and tachytachtic species.