Spawning Patterns Research Articles

Distribution and abundance of larval fish in the northern Aegean Sea--eastern Mediterranean--in relation to early summer oceanographic conditions

Two ichthyoplanktonic surveys were conducted during June 1995 and 1996 along the northern Aegean Sea coast with the aim of describing species composition, abundance and distribution patterns of the assemblages of fish larvae and their relationships to oceanographic regimes. The upper water column was generally cooler, fresher and richer in zooplankton during June 1996. The mean abundance of larvae of the small-sized pelagic fish (anchovy and most mesopelagics) was higher in 1996. In contrast, larvae of the middle-sized pelagics (Sardinella aurita, Trachurus mediterraneus, Scomber jaconicus and Auxis rochei) were more abundant in 1995. The eastern part of the surveyed area (NE Aegean Sea) was colder and less saline during both years because of the influence of Black Sea and riverine waters. In the colder June 1996, larvae of many summer spawners', e.g., the middle-sized pelagics, were present infrequently and at very low numbers in the NE Aegean Sea. Cluster analysis using the Bray-Curtis similarity index revealed well-defined groups of stations and assemblages of larvae. Ordination scores derived from non-metric multidimensional scaling were compared by multiple regression with various parameters and the analysis showed that taxonomic composition and abundance was primarily explained by bathymetry. In the cooler June 1996, a significant amount of variation in ordination scores was related to longitudinal differences in temperature, salinity and the width of the continental shelf. The membership of station and species groups defined by the cluster analysis differed between 1995 and 1996 and reflected interannual differences in the distribution and abundance of component species. Spatial and temporal spawning patterns of adults played the key role in the formation of assemblages of early larvae.

Comparison of the spawning patterns and fisheries biology of the sardine, Sardinops sagax, in temperate South Australia and sub-tropical southern Queensland

South Australia is the centre of the Australian distribution of Sardinops sagax, whereas southern Queensland is the northeastern edge of its local range. In South Australia, eggs were collected during all months and the peak in abundance coincided with the upwelling period in summer–autumn (January–April). In contrast, eggs were collected from southern Queensland only during winter–spring (August–November), when water temperatures fell below 23 °C. In South Australia, eggs were found throughout shelf waters, whereas in southern Queensland most eggs were collected from a small area between Noosa Heads and Caloundra. The South Australian fishery was confined mainly to the waters of southern Spencer Gulf and the Coffin Bay Peninsula, and the Queensland fishery was centred on the area of high egg density. Catch rates in the South Australian fishery were high throughout the year, whereas low catch rates were recorded in southern Queensland outside the spawning season. In South Australia, 50% of males and females were mature at approximately 146 and 150 mm FL, respectively. Over 70% of fish in all size classes collected from southern Queensland were sexually mature. Fish less than 145 mm FL comprised over 30% of South Australian catch, but less than 3% of fish taken from southern Queensland. Evidence is consistent with the hypothesis that S. sagax is a widely distributed resident of South Australian waters, but only migrates into southern Queensland during winter–spring to spawn.

Detecting and quantifying male sea urchin spawning with time-integrated fertilization assays

There has been much modeling and experimentation on factors affecting fertilization success in free-spawning marine invertebrates, but for many species spawning has rarely been observed in nature, if at all, and then mostly qualitatively. Understanding the dynamics of spawning and fertilization is especially important for species, such as the green sea urchin, Strongylocentrotusdroebachiensis (O.F. Muller), that have been widely depleted by harvesting. Time-integrated fertilization assays provide measures of sperm-availability adjacent to spawning populations for extended periods and with unprecedented temporal resolution. In such assays unfertilized eggs are held in baskets permeable to sperm and suspended in the water column as long as the eggs remain viable. In a consecutive series of 24- to 72-h assays the time course and spatial extent of sperm availability were measured near an aggregation of 250 sea urchins suspended in a cage at a field site in West Boothbay Harbor, Maine, USA. The assays were conducted in March and April, 2000, the spawning season of the green sea urchin. The distribution of embryonic stages within the assays revealed fine-scale temporal information on the timing of fertilization. The time series of multiple assays indicated that over a substantial portion of the spawning season there was an almost continuous low level of male spawning, a pattern consistent with a slow decline in gonad index observed in both male and female urchins. Fertilization rates averaged only 17% for the eggs in the basket nearest the spawning urchins (20 cm away), and the rates declined sharply over a distance of <1 m. Thus, despite the potential benefits of long egg life in integrating sperm supply over several days, the spatial effects on fertilization success were marked. Owing to the urchins' captivity and the lack of site replication, the generality of the observed spawning pattern must be confirmed. Nonetheless, the method lends itself to wider application among natural populations.

Reproduction of hatchery-reared and transplanted wild bay scallops, Argopecten irradians irradians, relative to natural populations

Efforts to restore bay scallop populations in the United States throughtransplantation of wild stock and reseeding of hatchery-reared individuals haveincreased due to declines in natural populations, yet little is known of thecomparative spawning patterns and relative reproductive investment of thesedifferent groups. In this study, spawning patterns of wild scallops from asource population in Northwest Harbor, New York and of scallops transplanted toa distant site in the same embayment (Flanders Bay) were similar.Hatchery-reared scallops held in pearl nets in Hallock Bay, New York showed thesame temporal spawning pattern and level of reproductive investment as scallopsfrom adjacent wild populations and wild scallops held in pearl nets. We suggestthat hatchery-reared scallops may be equally valuable as potential broodstockfor reseeding operations as wild scallops of the same size, provided thatappropriate conditioning and rearing practices are maintained. Both wild andhatchery-reared scallops may be transplanted a short period (i.e. 2–4weeks) prior to expected spawning to provide a source of potential broodstockinareas where natural population densities are low.

Temporal and Spatial Trends in Spawning Aggregations of Camouflage Grouper, Epinephelus Polyphekadion, in Pohnpei, Micronesia

The aims of this investigation were to document the temporal and spatial dynamics of aggregated camouflage grouper, Epinephelus polyphekadion in Pohnpei, Micronesia, and to assess seasonal and daily patterns of spawning and reproductive behavior. Camouflage grouper aggregated and spawned adjacent to the Kehpara Marine Sanctuary (KMS), Pohnpei, Micronesia, during two consecutive months in 1998 and 1999. A combination of gonadosomatic indices, oocyte diameter analysis, and histological evidence confirmed that camouflage grouper spawned 1–2 days prior to full moon over an 8–9 h period after dusk in each of the four study months. Males entered the site approximately 7 days prior to females and color variations were frequently observed. Significant differences were detected in mean size between the sexes. A series of management initiatives was initiated by the government in the 1980s to reduce fishing during aggregation periods, such as a March–April grouper sales ban, but these were largely ineffective. Following the 1998–1999 survey, several recommendations were made to halt aggregation fishing, including a commercial and subsistence catch and sales ban during spawning months, and the extension of the KMS to incorporate two additional grouper aggregations directly adjacent to it.

Pelagic eggs of marine fishes from Park Rynie, KwaZulu-Natal, South Africa: seasonal spawning patterns of the three most common species

For the period 1987 to 1998, pelagic eggs of marine fishes were collected from shelf waters at Park Rynie on the KwaZulu-Natal south coast. The three most numerous eggs collected were those of the mackerel Scomber japonicus,the sardine Sardinops sagax and the East coast roundherring Etrumeus teres. Together they comprised 67 % of all eggs collected. At times single-species egg densities were high, the highest accurately recorded was 850 eggs/cubic metre for S. sagax. All three species were predominantly winter to spring spawners. Theseasonal pattern of sardine eggs at Park Rynie suggests that after entering KwaZulu-Natal waters in June, sardines remain until November or December of each year before returning south to eastern Cape waters. Spawning in the East coast roundherring began in June, peaked in October to November, and tailed off in January. The mackerel showed a similar pattern of spawning, beginning in June and ending in December.

Experimental examination of interpopulation variation in reproductive timing of a fish

Many marine organisms have a specific reproductive timing, but its adaptive nature has not been directly tested because of the difficulty of manipulating reproductive timing in the field. Egg survival in relation to the timing of egg release in the puffer Takifugu niphobles, an intertidal spawner, was assessed by experimentally transplanting eggs to several tidal zones, and the observed pattern of variation in spawning time across environments (a pebble vs. a sandy beach) was examined to see if it was consistent with the presumed selection regime. The vertical distribution of eggs and the observation of spawning zones showed that substrate characteristics affected the fate of released eggs: at the pebble beach eggs were stranded in the high intertidal zone, while they were washed out toward the lower zone at the sandy beach. The egg-transplant experiment showed that egg survival was lower in the high zone than in the middle and low zones at both the pebble and sandy beaches, indicating that individual fishes should spawn earlier relative to the tidal cycle. However, the selection pressure for thefish to spawn earlier was more intense at the pebble beach than at the sandy beach, which was attributed to the difference between the beaches in the degree to which eggs were transported seaward. At the pebble beach (1) the timing of spawning was more strictly synchronized with the tidal cycle, (2) a day's spawning started, peaked, and ended earlier relative to the tidal cycle, and (3) a day's spawning was concentrated in a shorter time, than at the sandy beach. These temporal patterns of spawning are allexpected from the presumed selection regime across the beaches, suggesting that there is an evolutionary response of the trait to this selective force. This study explains interpopulation variation in reproductive timing of a marine fish by combining experimental manipulations of the reproductive timing with classic comparative methods. This experimental approach performed in different ecological settings is essential to further understanding of the ecology and evolution of temporal patterns of reproduction.

An overview of the living marine resources of Namibia

This paper gives an overview of the main living marine resources of Namibia. It focuses on the scientific research conducted during the past decade as input to the management of these resources. The distribution and habitats of the most important harvested species and the main seabird populations are briefly described and discussed. The life histories of the major exploited species are summarized, with emphasis on spatial and temporal spawning patterns, dispersal of early life stages, migration patterns of recruits and adults, and diet, the latter particularly as it relates to potential competition between species. A number of commercially important species, such as the hake Merluccius capensis and M. paradoxus, deep-sea red crab Chaceon maritae, West Coast rock lobster Jasus lalandii, skipjack tuna Katsuwonus pelamis, southern albacore Thunnus alalunga and to a lesser extent Cape horse mackerel Trachurus capensis, southern African sardine Sardinops sagax and Cape anchovy Engraulis capensis, are distribut...

Spawning timing of the cleaner wrasse, Labroides dimidiatus , on a warm temperate rocky shore

We observed spawning behaviors of the haremic cleaner wrasse Labroides dimidiatus at a rocky reef in southern Japan. Females released pelagic eggs daily from June to September after a spawning ascent by pairs. When the high tide occurred between noon and evening (quarter moon to new or full moon), they spawned around the time of the tide providing fast offshore currents. For the rest of the lunar cycle, spawnings occurred during late afternoon independent of the state of the tide at the time of day. This spawning pattern is quite different from that of conspecifics on coral reefs that always spawn around the high tide at all lunar stages to avoid potential egg predators. The wrasse ascended high in the water column, probably because of its predator-immune characters as a cleaner. The steep slope of the study site seemed to contribute to releasing gametes far above aggregating planktivores. Thus, gametes were not subject to heavy predation. Current direction might not always affect survival of spawned pelagic eggs on the temperate reefs so crucially as it does on coral reefs. We conclude that spawning during unfavorable tidal conditions during the daytime may be better than spawning during the best tidal condition in the crepuscular period when predation pressure on adults will be high. Intraspecific variation in the timing and location of spawning of the wrasse may result from different conditions for larval survival.

Spawning success in Atlantic salmon (Salmo salar L.): a long‐term DNA profiling‐based study conducted in a natural stream

Spawning success of Atlantic salmon (Salmo salar L.) was investigated, under near-natural conditions, in the Girnock Burn, an 8-km long tributary of the River Dee in Scotland. Employing minisatellite-based DNA profiling, mating outcomes were resolved over three spawning seasons by assigning parentage to progeny samples removed from spawning nests ('redds'). While individual spawning patterns differed markedly, consistent trends were present over the 3 years studied. Multiple spawning was found to be prevalent. More than 50% of anadromous spawners of both sexes contributed to more than one redd. Up to six redds for a single female and seven for a single male were detected. Both sexes ranged extensively. Distance between redds involving the same parent varied from a few metres to > 5 km. Distances > 1 km were common. Both males and females ranged to a similar extent. Range limit was not correlated to fish size. Pairs were not monogamous, both males and females mating with different partners at different sites. Size assortative mating was apparent among 1991 spawners but was not detected for 1992 or 1995. Redd superimposition was found to be common (17-22% of redds over the 3 years), although it was not correlated to the number of anadromous spawners present. High levels of nonanadromous mature parr mating success (40-50% of total progeny sampled) were recorded, and these likely contribute greatly to the effective population size. The relevance of these findings at the individual and population level is discussed, with particular reference to management implications.

Early Life History of the Northern Pikeminnow in the Lower Columbia River Basin

The northern pikeminnow Ptychocheilus oregonensis is a large, native cyprinid in the Columbia River basin that has persisted in spite of substantial habitat alterations. During the months of June to September 1993–1996, we investigated the temporal and spatial patterns of northern pikeminnow spawning, along with describing larval drift and characterizing larval and early juvenile rearing habitats in the lower Columbia River (the John Day and Dalles reservoirs and the free-flowing section downstream of Bonneville Dam) as well as in the lower sections of two major tributaries (the John Day and Deschutes rivers). The density of newly emerged drifting larvae was higher in dam tailraces (a mean of 7.7 larvae/100 m3 in surface tows) than in the lower reservoirs (0.3 larvae/100 m3), indicating that tailraces were areas of more intense spawning. Density was particularly high in the Bonneville Dam tailrace (15.1 larvae/100 m3), perhaps because adult northern pikeminnow are abundant below Bonneville Dam and this is the first tailrace and suitable main-stem spawning habitat encountered during upriver spawning migrations. Spawning also occurred in both of the tributaries sampled but not in a backwater. Spawning in the Columbia River primarily took place during the month of June in 1993 and 1994, when the water temperature rose from 14°C to 18°C, but occurred about 2 weeks later in 1995 and 1996, possibly because of cooler June water temperature (14–15°C) in these years. The period of drift was brief (about 1–3 d), with larvae recruiting to shallow, low-velocity shorelines of main-channel and backwater areas to rear. Larvae reared in greatest densities at sites with fine sediment or sand substrates and moderate- to high-density vegetation (a mean density of 92.1 larvae/10 m3). The success of northern pikeminnow in the Columbia River basin may be partly attributable to their ability to locate adequate spawning and rearing conditions in a variety of main-stem and tributary locations.

Pattern, synchrony and predictability of spawning of the tropical abalone Haliotis asinina from Heron Reef, Australia

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 213:193-202 (2001) - doi:10.3354/meps213193 Pattern, synchrony and predictability of spawning of the tropical abalone Haliotis asinina from Heron Reef, Australia Regina T. Counihan1,2, David C. McNamara1, Duncan C. Souter1,2, Edward J. Jebreen1, Nigel P. Preston2, Craig R. Johnson1, Bernard M. Degnan1,* 1Department of Zoology and Entomology, The University of Queensland, Brisbane, Queensland 4072, Australia 2Division of Marine Research, CSIRO, Cleveland, Queensland 4163, Australia *Corresponding author. E-mail: bdegnan@zoology.uq.edu.au ABSTRACT: The spawning biology of the tropical abalone Haliotis asinina on Heron Reef, Australia, was investigated to identify putative environmental and endogenous factors controlling spawning. Spawnings by H. asinina were highly regular and, in comparison to most other haliotids and marine invertebrates, frequent and extremely synchronous. These events appeared to be regulated by more than 1 environmental cue. The spawning season of H. asinina extends from October to April and is associated with an increase in water temperature. During the spawning season, recently captured abalone, housed in flow-through aquaria, released gametes for 2 nights every 2 wk during the new and full moons. However, the exact date of spawning did not correlate precisely with the lunar cycle. Occasionally the spawning events between 2 populations of H. asinina on Heron Reef that were 1.5 km apart differed by 1 d, suggesting that differential tidal regimes might influence the date of spawning. The population that was exposed to slightly longer spring low tides occasionally spawned 1 d earlier. In the aquaria, the onset of male spawnings was earlier than the onset of female spawnings by an average of 31 min. The time of spawning of either sex was highly correlated with the evening high tide; males spawned an average of 19 min prior to the high tide, and females spawned 11 min after the high tide. Spawnings were highly synchronous amongst individuals, with 90% commencing spawning within 89 min of the first individual that spawned. A greater percentage of individuals spawned when in the presence of the opposite sex and the frequency of male ejaculation was greater when in the presence of females. Synchronous spawning patterns persisted for 6 wk in H. asinina maintained in aquaria; after this period, spawnings continued but were irregular and asynchronous. We propose that low tide exposure and time of high tide indirectly regulate the date and time of spawning respectively, and that these tidal elements influence the spawning biology of H. asinina by maintaining endogenous rhythms that persist in non-tidal environments for at least 6 wk. KEY WORDS: Abalone · Mollusc · Spawning · Synchronous · Tidal cycle · Lunar cycle · Endogenous Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 213. Online publication date: April 04, 2001 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2001 Inter-Research.

Reproductive biology, early life-history and settlement distribution of sand flathead (Platycephalus bassensis) in Tasmania

The life-history ecology of P. bassensis was examined to determine the spatial and temporal patterns of spawning, larval transport and settlement distribution in coastal and continental shelf waters of southern and eastern Tasmania. Larval development is characterized by a large size at flexion and pelvic and dorsal fin formation, lightly pigmented trunk and tail and the absence of strong teeth on the roof of the mouth or lower jaw. The distribution of spawning fish and larvae and patterns of hydrography indicate that spawning occurs throughout estuaries, coastal embayments and inshore shelf waters of southern and eastern Tasmania. Larvae are concentrated in mid waters, which retain larvae inshore because cross-shelf subsurface currents are predominantly onshore. Spawning in P. bassensis occurred for up to six months between October and March. The broad range of lengths of 0+ fish in every month indicates that settlement occurred over an extended period, reflecting the protracted spawning period. Juveniles showed a preference for unvegetated habitats in nearshore waters, compared with beds of the seagrass Heterozostera tasmanica. Size compositions of 0+ fish indicate the presence of several cohorts in most months;this is discussed in terms of early life-history strategy and availability of settlement habitats.

Variation in egg spawning among subpopulations of sea urchins Strongylocentrotus droebachiensis: a theoretical approach

Variation in zygote production, by determining the initial size of the larval pool, can affect the population dynamics of marine invertebrates with a planktonic larval stage. In this paper, we model tem- poral and spatial patterns in egg spawning of the sea urchin Strongylocentrotus droebachiensis in the shal- low subtidal zone along the Atlantic coast of Nova Scotia. In this region, population outbreaks of sea urchins have caused major transitions from kelp beds to barrens (areas devoid of fleshy macroalgae). We define 3 community states and associated subpopulations of sea urchins: (1) the established kelp bed state, where sea urchins are in low density and small; (2) the transition state, with sea urchins in kelp beds, newly created (transitional) barrens, and grazing fronts (dense aggregations of large sea urchins along the edges of kelp beds); and (3) the barrens state after fronts have dispersed and intermediate densities of moderately sized sea urchins remain in post-transitional barrens. Using data from the literature and unpublished sources, we parameterize mathematical models to predict egg spawning for each subpopulation, both on an areal basis and for the entire coast. The predicted number of eggs spawned per m 2 is 1 order of mag- nitude higher in grazing fronts (7.1 〈 10 7 ) than in transitional and post-transitional barrens (5.8 〈 10 6 and 4.4 〈 10 6 , respectively), and 4 to 6 times higher in barrens than in established kelp beds (1.0 〈 10 6 ). Dif- ferences among subpopulations in the number of eggs spawned are directly related to differences in adult density, female gonad output, and body size. The total number of eggs spawned (all subpopulations com- bined) on a coastal scale increases ~6-fold from the established kelp bed state (5.6 〈 10 14 ) to the late tran- sition state (3.1 〈 10 15 ) and then drops slightly in the barrens state (2.4 〈 10 15 ). During most of the transition state, sea urchins in barrens spawn the greatest number of eggs. Based on published values, we estimate that fertilization rates are highest in grazing fronts (62%), intermediate in transitional and post-transitional barrens (36 and 43%, respectively) and lowest in kelp beds (15%), resulting in up to 2 orders of magnitude differences in the number of zygotes produced in these subpopulations (4.4 〈 10 7 , 2.1 〈 10 6 , 1.9 〈 10 6 , and 1.5 〈 10 5 ). Total zygote production (all subpopulations combined) on a coastal scale increases ~16-fold from the established kelp bed state (8.1 〈 10 13 ) to the late transition state (1.3 〈 10 15 ) and then drops slightly in the barrens state (1.1 〈 10 15 ). During most of the transition state, sea urchins in barrens contribute the great- est number of zygotes to the total zygote pool, with those in grazing fronts contributing up to 44% of all zygotes. Sensitivity analysis and evaluation of model assumptions indicate that our predictions should be correct in a relative sense (i.e. comparing among subpopulations), although absolute numbers may be over- estimated. A disparity between temporal patterns of estimated zygote production and observed settlement rates of S. droebachiensis in the shallow subtidal zone suggests that zygote production interacts with other factors to determine settlement rates of this species.

Patterns of brood production in the grass shrimp Palaemonetes pugio (Decapoda: Caridea)

Summary The pattern of brood production was analyzed in the grass shrimp Palaemonetes pugio. Determination of patterns of brood production as successive (spawning after each molt) or alternate (spawning after every other molt) was made by observations on individual females paired with males in the laboratory over a four-month period. A pattern of successive parturial (spawning) molts was the most common pattern. However, in a majority of these successive parturials, the ovary of the female was not mature at hatching of embryos from a previous brood. There was a delay of 10–11 days, during which ovarian maturation took place, between embryo hatching and the next (parturial) molt. This pattern of “slow successive” parturials does not result in the truly continuous brood production which occurs in many caridean species, i.e., spawning of a new brood within 1–2 days after hatching of a previous brood. However, there was a relatively low percentage of females in which the ovary was mature at embryo hatching. These latter females did have a parturial molt after only 2 days (“fast successive” parturial). In the “alternate” pattern, more frequent later in the 4-month observation period, hatching of embryos was followed by a non-parturial (without spawning) molt within 2 days, followed by an intermolt period of 10 days during which ovarian maturation occurred prior to the next (parturial) molt. The interval between spawns was similar in the “slow successive” and “alternate” parturial molt patterns (22–23 days) compared to a much shorter one (14–15 days) in the “fast successive” parturials. Examination of reproductive females from field samples indicated that the spawning pattern observed in the laboratory was that which occurs in natural populations in southern Louisiana. Although brood production in P. pugio is not truly continuous, the relatively short interspawn intervals observed still allow production of several broods during the breeding season.

Temporal and spatial genetic variation in spawning grounds of European hake (Merluccius merluccius) in the Bay of Biscay

Polymorphism at five microsatellite loci were screened to determine the genetic variability and the temporal stability of population structure in natural populations of European hake (Merluccius merluccius, L.) within the Bay of Biscay. In addition, the control region (900 bp) and two protein coding genes (ATPase, subunits 6 and 8, 842 bp and a partial sequence of the ND1, 800 bp) of the mitochondrial DNA (mtDNA) were sequenced from geographically distant populations from the extremes of the species range. One hundred individuals from either side of a supposed stock boundary within the bay were collected in autumn 1997. This sampling strategy was repeated during hake spawning seasons in late spring of 1998 and 1999. Low levels of population subdivision were found between putative populations within years. Similarly, low levels of differentiation were found between autumn 1997 northern samples and spring 1998 southern samples which were collected 7 months later on spawning grounds. These results are discussed in relation to ecological, behavioural and oceanographic information. Sampling effects, which may influence these results, are also discussed. Theta (theta) estimates were significantly different from zero in every other pairwise comparison between geographical areas (north and south of the Bay of Biscay) and between years within the same area (P<0.05). Hierarchical analysis of molecular variance (AMOVA) does not confirm the temporal persistence of population structure. These results are discussed in relation to variance in reproductive success, and temporal spawning patterns, which may exist within the bay. mtDNA variability was very low between geographically distant samples from Norway and the Mediterranean Sea with only 10 variable sites found in a total of 2542 bp of mtDNA, these differences being exclusively in the D-loop.

Seasonal timing of gametogenesis, spawning, brooding and glochidia discharge in Potamilus alatus (Bivalvia: Unionidae) in the Wheeler Reservoir, Tennessee River, Alabama, USA

Summary One hundred sixty-eight specimens of Potamilus alatus (Say, 1817) were collected approximately monthly from the Wheeler Reservoir (Tennessee River mile 298), Alabama, USA, between February 1995 and March 1996. Microscopic and gross examinations of gonadal tissue and marsupia were used to determine seasonal timing of gamete production, spawning, brooding and glochidia discharge. All individuals examined were dioecious. Spermatogenesis occurred between July and August. Spermatozoa numbers peaked in late August and male spawning occurred over a 2–3-week period in late August and early September. Oogenesis and female spawning had patterns similar to spermatogenesis and male spawning. Brooding of glochidia occurred between September and April. Glochidia discharge occurred in April and possibly early May, and coincided with the onset of the spawning season of the reported fish host, Aplodinotus grunniens (Rafinesque, 1819). The temporal patterns of gamete production and spawning in P. alatus of the subfamily Lampsilinae are in sharp contrast to members of the subfamily Ambleminae that have been similarly studied. This suggests that detailed studies of gamete production and spawning may be helpful in understanding unionid phylogeny and character evolution.

Fitness components of seasonal reproduction: an analysis using Nereis virens as a life history model

The reproductive cycles of the majority of marine invertebrates are strongly seasonal with highly synchronised patterns of spawning. It has become accepted that a distinction can be made between proximate factors and ultimate factors in the causation of seasonal reproduction. We briefly review these concepts and the hypotheses that have been developed about the nature of the ultimate factors that cause the fitness benefit and that ‘explain’ the adaptive significance of seasonal reproduction. We use a model based on the life history of the polychaete Nereis virens and demonstrate that seasonal reproduction may have impacts on adult components of fitness (i.e. reproductive value at age of first maturity), as well as on fertilisation rate and survival to age at first maturity. The results are discussed in the context of the programme PNDR and the related UK Natural Environment Research Council thematic programme ‘Developmental Physiology of Marine Organisms’ (NERC-DEMA). © 2000 Ifremer/CNRS/IRD/Éditions scientifiques et médicales Elsevier SAS life history / fitness / modelling / breeding / Nereis virens

POLA PENIJAHAN UDANG AIR TAWAR Macrobrachium sintangense De Man: PENGAMATAN SEMUSIM DI RANU KLINDUNGAN PASURUAN

The spawning pattern of Macrobrachium sintangense (de man) population in Klindungan pond (Ranu Klindungan) was observed. The number of eggs carrying female was count and high proportion of these female was found in August and February. This result indicate that there was two period of spawning in this population.

Small-scale spatial and temporal patterns in spawning of Atlantic cod (Gadus morhua) in coastal Newfoundland waters

Acoustic surveys were used to locate coastal Atlantic cod (Gadus morhua) spawning grounds and examine spatial and temporal patterns of spawning in Placentia Bay, Newfoundland, Canada. The same three grounds were used in 1997 and 1998 (Bar Haven in the inner bay and Cape St. Mary's and Oderin Bank in the outer bay). Grounds had densities &gt;0.1 fish·m-2 over scales of 100 m and &gt;13% of mature females in spawning condition. Ground use and spawning timing differed between years. Mean spawning female densities were highest at Cape St. Mary's in 1997 (1.6 × 10-2 fish·m-2) and Oderin Bank in 1998 (1.0 × 10-2 fish·m-2). At all grounds, spawning peaked earlier in 1997 (April) than in 1998 (June-July). In both years, cod spawned at sub- or near-zero temperatures. "Spawning columns" were observed at sites and times having high densities of spawning females. Sex ratios suggested that males arrived first and stayed later, while females followed when ready to spawn, accompanied by juveniles. Older females spawned earlier and later than younger females. Peaks in density of spawning females and the proportion of females spawning did not coincide. Hence, the location and timing of spawning cannot be quantified solely from the proportions of females in spawning condition.