Female Spawning Research Articles

Noise Affects Multimodal Communication During Courtship in a Marine Fish

Selection pressures on signals can be substantially modified by a changing environment, but we know little about how modified selection pressures act on multimodal signals. The currently increasing levels of anthropogenic noise in the ocean may affect the use of acoustic signaling relative to other modalities. In the Painted Goby (Pomatoschistus pictus), visual and acoustic signals are associated during courtship behavior, but females usually rely more heavily on acoustic signals than on visual signals in mate choice. In an aquarium experiment, we compared male courtship behavior and female spawning decisions between silent treatments and treatments with additional noise. We found that the relationships between male characteristics, male visual and acoustic courtship, and spawning success were affected by noise. A path analysis revealed that females pay more attention to visual courtship in noisy circumstances compared to control. We conclude that environmental stressors can cause shifts in the use of different signaling modalities for spawning decisions and discuss how selection pressures on multimodal signals may change with increasing noise-levels.

Spawning behavior of Arctic charr (Salvelinus alpinus): Spawning synchrony, vibrational communication, and mate guarding.

A mismatch in synchrony between male and female gamete release in external fertilizers can result in reduced or failed fertilization, sperm competition, and reduced paternity. In Arctic charr (Salvelinus alpinus), males can adopt either a guard or sneak tactic resulting in both pre‐ and postcopulatory competition between males with alternative reproduction tactics. Here, spawning behavior of free‐living Arctic charr was video‐recorded, and their reproductive behavior was analyzed. From evaluating 157 spawning events, we observed that females mainly spawned with a guarding male and that the female and the guarding male synchronized timing of gamete release under sperm competition. Although sneakers spawned with higher synchrony than the guarding male in single‐male spawning events, the average sneaker released his milt less synchronized with the female than the guarding male under sperm competition. Approximately 50% of the recorded spawning events occurred under sperm competition, where each event included an average of 2.7 males. Additionally, sneakers were more exposed to sperm competition than guarding males. An influx of males, in close proximity to the female, occurred during the behavioral sequences leading up to egg release, but this influx seemed not dependent on egg release, suggesting that something else than gonadal product attracts sneaker males to the spawning female. Just before and during the actual release of gametes, the spawning couple vibrates their bodies in close contact and it seems likely that this vibrational communication between the spawning couple, which results in a larger amplitude sound wave than seen under regular courting, reveals time of gamete release to sneaker males. Thus, vibrational communication may enable synchrony between the guarding male and the female, and this might be traded against the cost of higher detectability from surrounding sneaker males, eavesdropping in close proximity.

Some Aspects of Reproductive Biology of the Mudskipper Apocryptes Bato From the Coast of Chitagong

Some aspects of reproductive biology of the mudskipper Apocryptes bato (Hamilton 1822) from the coastal waters of Chittagong, Bangladesh was conducted. Disproportionate occurrence of male and female (1.20 : 1) was observed in the number of two sexes. A prolonged spawning season was found from June to early October with a single peak. The aspects in the ovary indicate one complete spawning of females in a single spawning season. The fecundity was found to vary from 7453 - 31195 with an average of 17590 ± 6867. Significant coefficient of correlation between the diameters of the eggs of corresponding anterior, middle and posterior regions of the right and left ovaries indicated the simultaneous release of eggs from both the ovaries. A much closer relationship of fecundity and the significant ‘t’ values indicated fecundity increases with the increase of total length, standard length, body weight and gonad weight.
 Asiat. Soc. Bangladesh, Sci. 44(1): 91-99, June 2018

Gonadal development and hermaphroditism of bluespotted seabream, Pagrus caeruleostictus (Valenciennes, 1830) from the Mediterranean Sea, Egypt

The bluespotted seabream Pagrus caeruleostictus represents one of the commercially significant Sparidea fish; however, studies on its reproduction are scarce. Accordingly, histological examination of female and male gonads was carried out for the first time in Egypt with the aim of describing the main gonadal changes during the reproductive cycle. The frequency of the distribution of maturity stages revealed that male and female reproductive cycles are divided into five maturity stages. The GSI and egg diameter data together with the maturity distribution, explained that the P. caeruleostictus is a fractional spawner with extended spawning season (June-October). Sex ratio was found to be unbalanced, being in favor of the females (1 male: 1.4 female); both males and females have parallel size distributions, with males being predominant and larger sizes. The size at first maturity (L50) was 27 cm and 29 cm total length (TL) for female and male fish, respectively. Absolute fecundity for ripe and spawning females ranged from 84,954 to 362,295 eggs, while the mean relative fecundity was 4970.864 ± 2398 egg/cm and 189 ± 54.38 egg/g to the total length and total weight, respectively. Gonadal histology distinguished rudimentary hermaphroditism for 83% of the young females, with evidence of low proportion of protogynous sex reversal for larger sizes. Results from the current research work provide essential basic information for the future of P. caeruleostictus fishery management and aquaculture plans.

Insight on reproductive strategy in Portuguese waters of a commercial protogynous species, the black seabream Spondyliosoma cantharus (Sparidae)

Information on fish reproductive strategy is essential to understand population dynamics. Samples of black seabream, Spondyliosoma cantharus, were collected from the western Portuguese continental coast to investigate the reproductive cycle, the timing of spawning, length at maturity and sex change, fecundity type and fecundity. This species is a protogynous hermaphrodite, showing a sharped biased sex ratio towards females for lengths smaller than 25 cm, and significantly biased towards males above this value, with no females occurring above 35 cm. Development of secondary growth follicles was asynchronous, and it was estimated that each female spawns 27 batches during the spawning season, which takes place from February to May. Half of the females’ population was mature at 18.41 cm and have changed sex at 25.62 cm. Sex change takes only a brief period of time, as transitional individuals were scarce and most showed oocytes regressing into cystic structures. The species presents a clear indeterminate fecundity type with massive atresia happening at the end of the spawning season. Mean values of 203 oocytes and 5431 oocytes by gram of eviscerated female were estimated for relative batch fecundity and relative annual fecundity, respectively.

REPRODUCTIVE ASPECTS OF THE TROPICAL ABALONE, HALIOTIS ASININA, FROM SOUTHERN LOMBOK WATERS, INDONESIA

The main objective of this study was to determine reproductive strategy including major spawning season of tropical abalone (Haliotis asinina) from southern Lombok waters, Indonesia. Gonad bulk index, maturity stages and oocyte size frequency distribution were applied to document gonadal development and major spawning season. The results of this study show that H. asinina in southern Lombok waters displayed year-round spawning with a high proportion occurring in August - November, when gonad index dropped to a lower level and high proportion of partly spawned and/or spent ovaries occurred in the population. Gonad development and spawning in males and females occurred synchronously. The correlation between gonadal development and environmental factors are described and discussed.

CHARACTERISTIC OF SPAWNERS FOR AMUR STURGEON ACIPENSER SCHRENCKII FROM WARM-WATER CAGE FARM IN THE PROCESS OF LONG-TERM EXPLOITATION

Cultivation, biological and production parameters of domesticated spawners of amur sturgeon in the age from 8 to 24 years are described for the warm-water cage farm conditions. In three year-classes bred from native spawners in the cages, the females mature firstly in the age 8–10 years, while males in the age 6–7 years. The females have larger body weight, length, girth, and fatness than males in all age groups from 8 to 24 years. The males are able to produce 40–350 mL of high-quality sperm per one drain-off session, while the firstmatured females produce 0.7–2.3 kg of eggs. Majority of the females (75 %) spawn annually or biennially. Average fecundity of the females in age 8–24 years is 200,000 eggs (3.82 kg, 7,500 eggs/kg), their average oosomatic index before spawning is 14.5. The females with the highest fecundity have the age 17–23 years and produce up to 520,000 eggs (7.0–10.5 kg, up to 13,500 eggs/kg), the highest oosomatic index is 24.5 %. In total, the females which reach the age 21–24 years produced on average 22–31 kg of roe in 6–8 spawnings that is equal to 90–98 % of their body weight, and the most productive ones (27 % of total number) produced 29–43 kg of roe, or 103–138 % of their body weight. The females are technologically welladaptable for maintenance. Their survival in the period of exploitation is 65 %.

Sperm whale depredation on longline surveys and implications for the assessment of Alaska sablefish

Sperm whales (Physeter macrocephalus) in the Gulf of Alaska depredate (remove or damage fish caught on fishing gear) on the annual National Marine Fisheries Service’s longline survey. Depredation can reduce sablefish (Anoplopoma fimbria) catch rates and increase uncertainty in survey-derived estimates of sablefish biomass. Using 27 years of longline survey data, this study: 1) evaluates fixed- and mixed-effects generalized linear models to estimate the effects of sperm whale depredation on the sablefish survey abundance; and 2) evaluates the impact of accounting for sperm whale depredation in the sablefish stock assessment. Model evaluation and simulations showed that mixed-effect models were far superior to fixed-effect models in terms of precision and confidence interval coverage. The estimated reduction in sablefish catch rate due to depredation was approximately 15%, which was considerably higher than previous estimates. Correcting for sperm whale depredation in the assessment resulted in a 2% increase in estimated female spawning biomass in the terminal year and a 3% higher quota recommendation, valued at approximately US $3 million. Accounting for sperm whale depredation in the sablefish assessment should be done in concert with estimating the increase in fishing mortality caused by depredation in the commercial fishery.

Noise can affect acoustic communication and subsequent spawning success in fish.

There are substantial concerns that increasing levels of anthropogenic noise in the oceans may impact aquatic animals. Noise can affect animals physically, physiologically and behaviourally, but one of the most obvious effects is interference with acoustic communication. Acoustic communication often plays a crucial role in reproductive interactions and over 800 species of fish have been found to communicate acoustically. There is very little data on whether noise affects reproduction in aquatic animals, and none in relation to acoustic communication. In this study we tested the effect of continuous noise on courtship behaviour in two closely-related marine fishes: the two-spotted goby (Gobiusculus flavescens) and the painted goby (Pomatoschistus pictus) in aquarium experiments. Both species use visual and acoustic signals during courtship. In the two-spotted goby we used a repeated-measures design testing the same individuals in the noise and the control treatment, in alternating order. For the painted goby we allowed females to spawn, precluding a repeated-measures design, but permitting a test of the effect of noise on female spawning decisions. Males of both species reduced acoustic courtship, but only painted gobies also showed less visual courtship in the noise treatment compared to the control. Female painted gobies were less likely to spawn in the noise treatment. Thus, our results provide experimental evidence for negative effects of noise on acoustic communication and spawning success. Spawning is a crucial component of reproduction. Therefore, even though laboratory results should not be extrapolated directly to field populations, our results suggest that reproductive success may be sensitive to noise pollution, potentially reducing fitness.

Exploring the effect of sampling, protogyny, and larval advection on stock estimates subject to no-take closures in a spatially complex coral reef line fishery on the Great Barrier Reef, Australia

Simulation is used to evaluate the ability of a two-region, age-structured assessment model to provide accurate and precise estimates of stock status (i.e., the ratio of female spawning biomass to unfished female spawning biomass) for coral trout (Plectropomus leopardus) on the Great Barrier Reef (GBR), Australia. The model used to generate the simulated data used by the assessment model is a spatially complex age- and sex-structured population dynamics model that captures the protogynous nature of coral trout. Stock status is underestimated (negatively biased), with the extent of negative bias related to mis-specification of the breeding strategy of the target fish stock, the impact of the amount of larval connectivity among reefs, the number of reefs closed to fishing, as well as exploitation rates. The estimates of stock status were less negatively biased when fishery-independent index and age- and length-composition data were available from closed areas. The results will inform the development of management strategies for coral trout in the GBR and highlight the importance of basing evaluations of estimation and management performance on operating models that capture ecologically important processes such as metapopulation dynamics and protogynous life history.

Age, growth, mortality and reproductive seasonality of jolthead porgy, Calamus bajonado, from Florida waters.

Ages of jolthead porgy (Calamus bajonado Schneider 1801) (n = 635) from Florida commercial and recreational fisheries from 2008–2016 were determined using sectioned sagittal otoliths. We determined, using edge-type analysis, that opaque zones were annular, forming March–June (peaking in April). Jolthead porgy ranged from 1–13 years, and the largest fish measured 680 mm TL (total length, mm). Body size relationships for jolthead porgy were TL = 1.09FL + 20.44 (n = 622, r2 = 0.99), FL = 0.90 TL –14.26 (n = 622, r2 = 0.99), and W = 1.1 × 10−5 TL3.06 (n = 577), where W is total weight (grams, g) and FL is fork length (mm). The von Bertalanffy growth equation for jolthead porgy was Lt = 737(1 − e−0.14(t+2.02)) (n = 635). Point estimate of natural mortality was M = 0.32, while age-specific estimates of M ranged from 0.58–0.17 y−1 for ages 1–13. Catch curve analysis estimated the instantaneous rate of total mortality Z = 0.70, while instantaneous rate of fishing mortality F was 0.38. Macroscopic staging of female gonads indicated the presence of hydrated oocytes from December–March, and GSI data indicates that peak spawning in females occurs during March. This study presents the first published findings of life history parameters for jolthead porgy from the Atlantic waters off the southeastern United States.

Intra- and Intersexual swim bladder dimorphisms in the plainfin midshipman fish (Porichthys notatus): Implications of swim bladder proximity to the inner ear for sound pressure detection.

The plainfin midshipman fish, Porichthys notatus, is a nocturnal marine teleost that uses social acoustic signals for communication during the breeding season. Nesting type I males produce multiharmonic advertisement calls by contracting their swim bladder sonic muscles to attract females for courtship and spawning while subsequently attracting cuckholding type II males. Here, we report intra- and intersexual dimorphisms of the swim bladder in a vocal teleost fish and detail the swim bladder dimorphisms in the three sexual phenotypes (females, type I and II males) of plainfin midshipman fish. Micro-computerized tomography revealed that females and type II males have prominent, horn-like rostral swim bladder extensions that project toward the inner ear end organs (saccule, lagena, and utricle). The rostral swim bladder extensions were longer, and the distance between these swim bladder extensions and each inner-ear end organ type was significantly shorter in both females and type II males compared to that in type I males. Our results revealed that the normalized swim bladder length of females and type II males was longer than that in type I males while there was no difference in normalized swim bladder width among the three sexual phenotypes. We predict that these intrasexual and intersexual differences in swim bladder morphology among midshipman sexual phenotypes will afford greater sound pressure sensitivity and higher frequency detection in females and type II males and facilitate the detection and localization of conspecifics in shallow water environments, like those in which midshipman breed and nest.

Interannual variability in reproductive traits of the Patagonian toothfish Dissostichus eleginoides around the sub-Antarctic island of South Georgia.

Commercial fisheries data, collected as part of an observer programme and covering the period 1997-2014, were utilized in order to define key reproductive traits and spawning dynamics of the Patagonian toothfish Dissostichus eleginoides at South Georgia. Multi-year spawning site fidelity of D. eleginoides was revealed through the identification of previously unknown spawning hotspots. Timing of female spawning was shown to have shifted later, leading to a shorter spawning duration. A decrease in length and mass of female and male spawning fish and a reduced number of large spawning fish was found, evidence of a change in size structure of spawning D. eleginoides. During the study period fewer later maturity stage females (including spawning stage) were observed in conjunction with increased proportions of early stage female D. eleginoides. The findings are discussed in the context of reproductive success, with consideration of the possible effects such spawning characteristics and behaviours may have on egg and larval survival. This work presents the first long-term assessment of D. eleginoides spawning dynamics at South Georgia and provides valuable knowledge for both the ecology of the species and for future fisheries management of this commercially important species.

Sperm-limited males save ejaculates for future matings when competing with superior rivals

Adjusting ejaculates to sperm competition can lead to sperm limitation. Particularly in polygynous species, males may face a trade-off between investing sperm in current or future mating opportunities. The optimal sperm allocation decision should depend on the relative intensity of sperm competition experienced in a mating sequence. Here we asked how males respond to this trade-off in polygynous fish with alternative male mating tactics, intense sperm competition and sperm limitation. Large bourgeois males of the shell-brooding cichlid Lamprologus callipterus build nests consisting of empty snail shells, in which females spawn and raise offspring. During spawning, nest males release ejaculates into the shell opening. Genetically distinct, parasitic dwarf males enter shells during spawning to fertilize the eggs from inside the shell. These dwarf males were previously shown to be superior sperm competitors to nest males. Here we showed that when spawning with several females simultaneously, nest males reduced the spawning duration for each clutch and the number of ejaculations per female tended to decrease, reflecting sperm limitation. Experimental exposure of nest males to sperm competition with dwarf males reduced the number and duration of ejaculations by roughly half. Hence, when exposed to competition with a superior rival, nest males did not increase their sperm expenditure as predicted by sperm competition risk models, but in fact saved sperm for future mating opportunities as predicted by sperm competition intensity theory. This seems to be adaptive because of the considerable sperm demands in this species, which is partly due to their high degree of polygyny.

Maternal contribution to spawning and early life-history strategies of the genus Lepidonotothen (Nototheniidae, Perciformes) along the southern Scotia Arc

The coastal fish community of the southern Scotia Arc, including the South Shetland Islands and the Bransfield Strait, is composed of the genus Lepidonotothen, which consists of three widely overlapping species such as L. kempi, L. larseni and L. nudifrons. The life-history strategies of these species driven by environmental and inter-specific interactions remain poorly known. In this paper, we estimate the maternal contribution to spawning of adult females in terms of fecundity and egg size through macroscopic and histological analyses of gonads. We further investigate the size and timing of hatching, growth rate and duration of the larval stage through microstructure analysis of sagittal otoliths collected from larval samples. All three species produced eggs of relatively small size at hatching, showing a trade-off between egg size and fecundity. Total fecundity was positively related to fish size during growth, as well as to maximum size. Female gonad investment was comparable among the species, as they all start spawning at about 65% of their maximum size with a similar gonadosomatic index. All species generated small larvae (altricial) which hatched over widely different periods, resulting in a temporal succession of larval occurrence. Compared to L. kempi, the other two species had relatively slow-growing larvae. Only L. kempi and L. larseni produced overwintering larvae. Differences in maternal contribution to spawning and early life-history traits of these species contribute to reduce interspecific competition for food through ecological niche partitioning.

Assessing the effect of environmental factors on the spawning activity of the sea urchin Strongylocentrotus intermedius through video recording observations

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 588:101-119 (2018) - DOI: https://doi.org/10.3354/meps12436 Assessing the effect of environmental factors on the spawning activity of the sea urchin Strongylocentrotus intermedius through video recording observations Peter M. Zhadan1,*, Marina A. Vaschenko2, Sergey D. Ryazanov1 1V. I. Il’ichev Pacific Oceanological Institute, Far Eastern Branch, Russian Academy of Sciences, 43 Baltiyskaya Street, 690041 Vladivostok, Russia 2National Scientific Center of Marine Biology, A. V. Zhirmunsky Institute of Marine Biology, Far Eastern Branch, Russian Academy of Sciences, 17 Palchevsky Street, 690041 Vladivostok, Russia *Corresponding author: pzhadan@poi.dvo.ru ABSTRACT: We used video recordings of spawning behaviour of the sea urchin Strongylocentrotus intermedius conducted in parallel with an analysis of gonadal state and measurement of environmental variables (tidal level, phytoplankton, temperature, salinity and oxygen concentration) in situ to study the role of environmental factors in triggering sea urchin spawning. The observations were performed during 3 reproductive seasons, each of 2 mo duration, in 2 bays with different levels of phytoplankton (measured as chlorophyll a [chl a]). The only significant positive correlation found was between sea urchin spawning frequency and chl a concentration. Despite a high level of gonad maturity, sea urchin spawning was rarely recorded in the bay with low levels of chl a whereas mass spawning occurred in the bay with higher chl a concentration, with the peak of spawning activity centred around the full moon. Spawning was predominantly nocturnal. Immediately before and during spawning, males actively moved. Females began to spawn only when there were several spawning males nearby. In both sexes, each spawning event included several episodes of gamete release of different duration and with different intervals between them. The same male likely can participate in several spawning events. The following hierarchy of drivers of S. intermedius spawning activity was revealed: (1) increasing the phytoplankton concentration induced active motion and spawning in males, (2) both an elevated phytoplankton level and the presence of sperm stimulated spawning in females and (3) the night time and the new and full lunar phases increased the probability of spawning. KEY WORDS: Broadcast spawning · Echinoderms · Reproductive synchrony · Phytoplankton · Temperature · Circadian rhythm · Lunar cycle Full text in pdf format Supplementary material PreviousNextCite this article as: Zhadan PM, Vaschenko MA, Ryazanov SD (2018) Assessing the effect of environmental factors on the spawning activity of the sea urchin Strongylocentrotus intermedius through video recording observations. Mar Ecol Prog Ser 588:101-119. https://doi.org/10.3354/meps12436 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 588. Online publication date: February 08, 2018 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2018 Inter-Research.

Spawning and early development of the West Indian top shell,Cittarium pica(Linnaeus, 1758), under ex-situ conditions

The West Indian top shell, Cittarium pica , is an endangered vetigastropod from the rocky intertidal Caribbean. In order to provide a basis for its hatchery-production as a conservation tool, spawning and early development were evaluated under ex-situ conditions. Spawning response was monitored during different lunar phases with application of physical and chemical stimuli – such as changes in temperature salinity and desiccation, exposure to UV irradiated water and chemical stimulation with Tris and hydrogen peroxide. Spawning response was obtained in association with daytime, new moon, flooding and high tides. Use of physical and chemical stimuli did not elicit any spawning response. Adults conditioned in the hatchery for one year did not spawn. Spawning of males and females was simultaneous and frequently intermittent. On average, percentage and size of spawn was higher for males than females. Fecundity was positively correlated with total female wet weight, with an average value of 149 000 oocytes per female. Embryonic and larval development was reported in detail. Results suggest that there is a high potential to use the controlled ex-situ reproduction of C. pica as a conservation tool, since gamete and larvae were repeatedly obtained from wild adults collected days before new moon following a circadian endogenous pattern applying simple protocols of spawning, fertilization and incubation.

Quantitative determination of ovarian development in penaeid prawns (Decapoda: Penaeidae)

We developed histological methods to increase precision in measuring oocyte size and, for the first time, quantify changes in oocyte composition during ovarian development in penaeids. Wild-caught female Metapenaeus dalli Racek, 1957 from the Swan-Canning Estuary, Perth, Western Australia were used as a model species to compare the novel method to traditional techniques. Morphological analysis showed that ovarian development in M. dalli occurs in five stages: immature, early maturing, late maturing, mature, and post spawning, which is consistent with other penaeids. Analysis of key morphometric parameters of length and Gonad Somatic Index (GSI) showed that GSI provided the strongest discriminators of ovarian development. Oogenesis was similar to qualitative descriptions of other penaeid prawns and most-closely related to previous descriptions of Metapenaeus affinis Milne Edwards, 1837. Comparisons between the novel perimeter tracing and traditional single linear methods for measuring oocyte dimensions showed that greater precision was achieved by tracing. This resulted in a 17-40% reduction in the confidence limits of the means for all cell types measured. A novel histological technique of examining oocyte composition was also developed. This technique allowed for the relationship between stages of ovarian development and proportion by volume of oocyte types to be determined. The difference in the proportions of cell types between each stage of ovarian development was found to be statistically significant, except between immature and post spawning females. The novel methods developed in this study provide new opportunities in the study of ovarian development in penaeids and possibly in other species.

Life-history traits of the long-nosed skate Dipturus oxyrinchus.

This work investigates life-history traits of the long-nosed skate Dipturus oxyrinchus, which is a common by-catch in Sardinian waters. The reproductive variables were analysed from 979 specimens sampled during scientific and commercial hauls. Females (10·4-117·5 cm total length, LT ) attained larger sizes than males (14·5-99·5 cm LT ). To evaluate age and growth, a sub-sample of 130 individuals (76 females and 54 males) were used. The age was estimated by annuli counts of sectioned vertebral centra. Four models were used for the length-at-age data: the von Bertalanffy, the exponential, the Gompertz and the logistic functions. According to the Akaike's information criterion, the Gompertz model seemed to provide the best fitting curve (L∞ mean ± s.e.: 127·55 ± 4·90 cm, k: 0·14 ± 0·09, IP: 3·97 ± 0·90 years). The oldest female and male were aged 17 (115·5 cm LT ) and 15 years (96·0 cm LT ), respectively. Lengths at maturity were 103·5 cm for females and 91·0 cm for males, corresponding to 90% of the maximum observed length in both sexes. The monthly distribution of maturity stages highlighted an extended reproductive cycle, with spawning females and active males being present almost throughout the year, as confirmed by the gonado-somatic index. Ovarian fecundity reached a maximum of 26 yolked follicles with a mean ± s.e. size of 19·7 ± 6·5 mm.

Gametogenic cycle of the rough cockle <em>Acanthocardia tuberculata</em> (Mollusca: Bivalvia) in the M’diq Bay (SW Mediterranean Sea)

The reproductive cycle of Acanthocardia tuberculata (Linnaeus, 1758) was studied in M’diq Bay. The gonadal development was determined by means of standard histological techniques, mean oocyte diameters and a condition index. Rough cockle is a gonochoric species with synchronous gonadal development and spawning in males and females. The sex ratio obtained was not significantly different to 1:1. Gametogenesis began in late winter (November) coinciding with the temperature drop. In June, with increasing sea water temperature, most of the population was spent and resting oocytes appeared dispersed in the gonad. Resting stage occurred from August to October, during which time sex could not be determined in 100% of the population. A. tuberculata showed a clear seasonality in its gametogenic cycle, with one spawning peak per year in June. Quantitative measurements of 6318 oocyte diameters indicated the patterns of development observed in the qualitative staging. The results obtained revealed the direct influence of temperature on the reproductive cycle. First sexual maturity occurred at 42.77 mm shell length. The information gathered in this study allowed preliminary management measures to be suggested for the fishery of this species, including a closed season during the main spawning season (May-June) and the establishment of a minimum landing size (at least 50 mm shell length) for A. tuberculata from the Moroccan Mediterranean coast.