Winter Spawning Research Articles

Thermal tolerance during early ontogeny in the common whelk Buccinum undatum (Linnaeus 1785): Bioenergetics, nurse egg partitioning and developmental success

Temperature is arguably the primary factor affecting development in ectotherms and, as a result, may be the driving force behind setting species' geographic limits. The shallow-water gastropod Buccinum undatum is distributed widely throughout the North Atlantic, with an overall annual thermal range of below zero to above 22°C. In UK waters this species is a winter spawner. Egg masses are laid and develop when sea temperatures are at their coolest (4 to 10°C) indicating future climate warming may have the potential to cause range shifts in this species. In order to examine the potential impacts of ocean warming, we investigate the effects of temperature on the early ontogeny of B. undatum across a thermal range of 0 to 22°C. Each egg mass consists of approximately 100 capsules, in which embryos undergo direct development. Successful development was observed at temperatures ranging from 6 to 18°C. Rates of development increased with temperature, but the proportion of each egg mass developing successfully decreased at the same time. With increasing temperature, the mean early veliger weight increased, but the number of early veligers developing per capsule decreased, suggesting a negative impact on the number of crawl-away juveniles produced per capsule. Elemental analysis showed both carbon (C) and nitrogen (N) to increase with temperature in early veligers but not in hatching juveniles, indicating greater energy reserves are accumulated during early ontogeny to compensate for the higher energetic demands of development at higher temperature. The developmental plasticity observed in B. undatum suggests this species to be capable of adapting to temperatures above those it currently experiences in nature. B. undatum may possess a thermal resilience to ocean warming at its current upper temperature distribution limit. This thermal resilience, however, may come at the cost of a reduced offspring number.

The effect of temperature on sperm motility and enzymatic activity in brown trout Salmo trutta, burbot Lota lota and grayling Thymallus thymallus

The effect of temperature on sperm motility was investigated in brown trout Salmo trutta, burbot Lota lota and grayling Thymallus thymallus using water and sperm motility prolonging saline solution (SMPS) for motility activation. The effect of temperature (4-20° C) on spermatozoal enzymes for energy supply [malate dehydrogenase (MDH), pyruvate kinase (PK), adenylate kinase (AK)], flagellar movement [Mg(2+) adenosine triposphatase (ATPase)] and oxidative defence [peroxidase (POX)] were measured in S. trutta and L. lota. Temperatures yielding the highest initial sperm motility rates and swimming velocities were 4-6° C for S. trutta [investigated range (IR) = 4-12° C] and L. lota (IR = 2-8° C) and 8-16° C (IR = 4-16° C) for T. thymallus. Motility variables were re-measured after 30 s in S. trutta, after 45 s in T. thymallus and after 60 s in L. lota in water and after 2 min in all investigated species in SMPS. Motility variables were increased by low temperatures and the results differed between water and SMPS. In S. trutta and L. lota, the temperature resulting in highest activities of MDH, PK, AK and ATPase was 4° C. POX had a very narrow temperature optimum at 20° C in both species. This may indicate that the temperature optimum of enzymes of energy supply and flagellar movement are closely related to motility. The present data show that the variables are affected by temperatures in an ecologically relevant range. Too low, as well as too high temperatures affected sperm motility, and the winter spawners (S. trutta and L. lota) have a narrower temperature optimum than the spring spawner T. thymallus.

황해에서 어획된 살오징어의 생물학적 특성

We investigated the biological characteristics of the squid, Todarodes pacificus Steenstrup through the samples caught monthly in the Yellow Sea( 30`N, 30`N, ) from 1985 to 1987. Monthly mantle length frequency were separated into Autumn spawning group and winter spawning group with Tanaka`s method(1956) to determine the main group of the squids caught in the Yellow Sea. The ratio of winter spawning group was higher than that of autumn spawning group. Monthly gonadosomatic index of females increased on July in 1985, on October in 1986, and October in 1987 and decreased later in each year. That of males increased on June in 1985, on July in 1986, and June in 1987. The length of 50% group maturity of female was 20.7 cm mantle length(ML) in 1985, 17.9 cm ML in 1986, and 17.2 cm ML in 1987. The ratio of female was higher than that of male in the group over 24 cm ML, and the ratio of male was higher than that of female in the group under 24 cm ML. We concluded that the length of 50% group maturity of squids was affected by the density of the population status.

Trace elements in the statoliths of jumbo flying squid off the Exclusive Economic Zones of Chile and Peru

Ontogenetic variation in 4 trace element ( 88 Sr, 137 Ba, 24 Mg, 23 Na) concentrations and their ratios to Ca were measured in statoliths of the jumbo flying squid Dosidicus gigas off the Exclu- sive Economic Zone of Chilean and Peruvian waters using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The element compositions of statoliths showed no significant differ- ences between females and males. All of the elements in different growth zones showed significant variations, except for Mg. Sr:Ca and Mg:Ca were good indicators for distinguishing squid from autumn and winter spawning seasons. Sr:Ca and Ba:Ca distribution patterns in statoliths confirmed that paralarvae and juvenile squid inhabit surface waters, while subadult squid migrate into deeper waters. An increasing Sr:Ca ratio of subadult squid could be explained by declining temperature gra- dients from northern to southern sampling locations, although no significant Sr:Ca differences were observed (p > 0.05). Mg:Ca ratios decreased progressively from the nucleus to the peripheral zone, which might be correlated with statolith growth rates. Na:Ca ratios slightly declined from paralarvae to the subadult phase. Quantitative relationships between statolith trace elements and environmen- tal conditions under different growth stages are needed to improve our understanding of life history of D. gigas.

The rediscovery of Oncorhynchus kawamurae, Kunimasu: problems and perspectives for its conservation

It is almost a miracle that T. Nakabo, K. Nakayama, N. Muto, and M. Miyazawa (2011) have discovered an extant population of Oncorhynchus kawamurae, or Kunimasu as the standard Japanese name, from Lake Saiko, Yamanashi Prefecture, Japan, from outside of its original distribution. Kunimasu had been believed to be extinct for more than 70 years in the type locality (and only known locality), Lake Tazawa, Akita Prefecture, owing to the introduction of strongly acidic water to the lake. This great discovery is certainly epoch-making in the study of the conservation of threatened freshwater fishes in Japan. The extant population seems to be safe so far under the conditions of local fishery activity in Lake Saiko. Nakabo et al. (2011) basically succeeded in clarifying both the morphological distinction and genetic isolation of Kunimasu from those of another sympatrically occurring kokanee, Oncorhynchus nerka, or Himemasu, which was also introduced to Lake Saiko from Hokkaido before World War II. Those facts consequently confirm the specific (not subspecific) status (sensu Mayr 1942, 1969) of Kunimasu as O. kawamurae, referring to some ecological peculiarity, i.e., deep swimming/spawning layer and spawning in winter or spring. However, its basic biology remains too obscure, so the information to certify them as O. kawamurae and subsequent protection for this valuable extant population is not yet sufficient. Major problems are as follows. (1) Genetic property: The small number of the specimens examined (n = 9) is not sufficient to show their full population genetic traits. Nakabo et al. (2011) successfully rejected large-scale hybridization between Kunimasu and Himemasu in Lake Saiko. The presumed differences in spawning season and sites may have worked as reproductive isolation mechanisms. However, their data cannot rule out the possibility that they have partially hybridized and some gene introgression from Himemasu to Kunimasu (and vice versa) has occurred. A huge number of Himemasu had already been introduced even to Lake Tazawa for a period of 30 years (Sugiyama 2000). Only morphologically typical specimens might have been examined by Nakabo et al. (2011). Information on the founder effect during the introduction process is lacking for both Kunimasu and Himemasu in Lake Saiko. Taking into consideration the repeated artificial transplantation of Himemasu among several lakes, the original geographic variation of Himemasu should be clarified, and the Kunimasu population in Lake Saiko should be compared with it by using adequate molecular markers. Verifiable information on the presence/ absence or extent of gene introgression is essential when reintroduction or conservation/benign introduction of this ‘‘extinct in the wild’’ species is considered. It has not been concluded yet whether the Kunimasu population in Lake Saiko is genetically pure. Genetic comparison between the current and original Kunimasu specimens would be the only direct test to certify the ‘‘rediscovery.’’ DNA analysis for old formalin-fixed specimens is generally difficult or impossible (Sugiyama 2000). However, recently developed next-generation sequencers might have the power to pick up and sequence short DNA fragments even from such old specimens. K. Hosoya Nature Conservation Committee of the Ichthyological Society of Japan, Tokyo, Japan

Phenological changes in intertidal con‐specific gastropods in response to climate warming

AbstractThere is substantial evidence from terrestrial and freshwater systems of species responding to climate change through changes in their phenology. In the marine environment, however, there is less evidence. Using historic (1946–1949) and contemporary (2003–2007) data, collected from rocky shores of south‐west Britain, we investigated the affect of recent climate warming on the reproductive phenology of two con‐specific intertidal limpet grazers, with cool/boreal and warm/lusitanian centres of distribution. Reproductive development in the southern limpet, Patella depressa, has advanced, on average, 10.2 days per decade since the 1940s, with a longer reproductive season and more of the population reproductively active. The peak in the proportion of the population in advanced stages of gonad development was positively correlated with sea surface temperature (SST) in late spring/early summer, which has increased between the 1940s and 2000s. The advance in peak reproductive development of this species is double the average observed for terrestrial and freshwater systems and indicates, along with other studies, that marine species may be responding faster to climate warming. In contrast, the northern limpet, Patella vulgata, has experienced a delay in the timing of its reproductive development (on average 3.3 days per decade), as well as an increase in reproductive failure years and a reduction in the proportion of the population reaching advanced gonad stages. These results are the first to demonstrate a delay in the reproductive development of a cool‐temperate, winter spawner, towards cooler more favourable environmental conditions in response to climate warming. Such a delay in spawning will potentially lead to trophic miss‐matches, resulting in a rapid nonlinear decline of this species.

An evaluation of the daily egg production method to estimate spawning biomass of snapper (Pagrus auratus) in inner Shark Bay, Western Australia, following more than a decade of surveys 1997–2007

The daily egg production method (DEPM) has been used to estimate spawning biomass of separate stocks of snapper (Pagrus auratus) in the inner gulfs of Shark Bay, Western Australia, since 1997. While these stocks have been targeted by a regionally important recreational fishery since at least the 1970s, no information on stock size was available prior to this application of the DEPM. Ichthyoplankton surveys were undertaken during the winter spawning periods standardised around the new moon and used a stratified-systematic approach combined with more intensive, fine-scale sampling in the vicinity of the known spawning locations. Samples of mature snapper were collected concurrently using rod and line fishing with the assistance of volunteer recreational fishers. Daily egg mortality and daily egg production (P) were estimated using both non-linear least squares regression and generalized linear models for comparison. While relatively imprecise, mostly due to imprecision in the estimation of P, spawning biomass estimates have confirmed that these stocks are relatively small (measured in 10–100s of tonnes) compared with snapper stocks elsewhere in Australia and New Zealand. The DEPM-based estimates have been combined with biological (age composition) data and catch information in integrated stock assessment models that have underpinned the management of these snapper stocks and the associated recreational fishery since 2002. Under the highly conservative TAC-based management regime that has been in place since 2003, spawning stocks in the Eastern Gulf and Denham Sound have been rebuilt to the management target level while the Freycinet Estuary stock is steadily rebuilding. The utility and cost of the DEPM is briefly discussed in relation to the use of tagging as an alternate assessment method, to determine the most cost-effective and tractable approach for monitoring the status of these important snapper stocks into the future.

Reproduction of the Egyptian Sole,<I> Solea Aegyptiaca</I> (Actinopterygii: Pleuronectiformes:soleidae), from Port said, Egypt, Mediterranean Sea

Background. Understanding of reproduction of the Egyptian sole, Solea aegyptiaca, has been considered a major step toward understanding its population dynamics, especially in the eastern Mediterranean Sea. In Egypt this species has highly commercial value and it has recently been successfully bred in aquaculture, but more data on the reproductive biology is still needed. So, the present work aimed to study the population structure and the reproductive dynamics of S. aegyptiaca over an annual reproductive cycle. Materials and methods. A total of 594 specimens of S. aegyptiaca were obtained from October 2004 to September 2005 in a monthly basis from the commercial catch. Sex ratio, age, and length at first maturity, gonado-somatic index, maturity stage, oocyte diameter, and fecundity were analysed in order to increase our knowledge on the reproductive dynamics of S. aegyptiaca. Results. The overall ratio between males and females was 1.0 : 1.15 and showed no significant deviation from the expected 1 : 1 ratio, males are dominant among small size, while females are dominant among larger size. Females attained their maturity at the length of about 15.0 cm. The reproductive activity of S. aegyptiaca took place between January and June with a peak on January, when the majority of oocyte growth (> 400 μm in diameter) occurred. Hydrated oocytes reach 1000 μm immediately before spawning. Absolute fecundity ranged from 9898 to 38505 and can be expressed as a function of total length. Conclusion. S. aegyptiacais a winter spawner, and the female attains its maturity at 15.0 cm of total length. So, fishing should be prohibited during the period from January to June to conserve the existing stock of the target species. Regulations should also be directed to reduce the fishing potential of 18.0 cm total length. It is important to give each fish the chance to reproduce at least once in its lifetime.

Threatened fishes of the world: Salvelinus confluentus (Salmoninae)

Common name: Bull Trout; Bull Charr. Conservation status: Vulnerable IUCN Red List; Threatened, U.S. Fish and Wildlife Service (1999). Identification: Adults to 14 kg, olive green to brown body fading to white on belly with yellow spots dorsally grading to red to orange laterally. White leading edges on rayed fins, solid colored dorsal fin (Cavender 1978; Markle 1992) (Illustration: copyright Joseph R. Tomelleri). Distribution: Northern California to Alaska, eastward extent Nevada, Montana, and Idaho (Cavender 1978; Haas and McPhail 1991). Canadian distribution includes British Columbia, Central Northwest Territories, and western Alberta (Reist et al. 2002). Currently extirpated from California with local extirpations scattered throughout the remainder of the species’ range (USFWS 1999). Habitat and ecology: Highly variable movement behavior spanning a continuum between resident and migratory individuals. Spawning and rearing confined to colder ( 12 years (Zymonas 2006). Autumn to early winter spawning in headwater streams (Fraley and Shepard 1989; McPhail and Baxter 1996). Fecundity ranges from 2,000 to 12,000 eggs, with emergence of fry in late winter to early spring (Fraley and Shepard 1989). Threats: Threats include angling (Schmetterling and Long 1999), habitat loss and fragmentation (Dunham and Rieman 1999), nonnative trout, hybridization (Baxter et al. 1997), disease (Post et al. 2003; USFWS 1999), and pollution (Post et al. 2003; USFWS 1999). Bull trout are particularly vulnerable to threats due to long embryo incubation, relatively old age at maturity and reliance on pristine habitat (Pratt 1992; Rieman and McIntyre 1993). Conservation actions and recommendations: Address known threats, public outreach, research evolutionary history, ecology, and conservaEnviron Biol Fish (2010) 89:161–162 DOI 10.1007/s10641-010-9708-8

The Charr Problem Revisited: Exceptional Phenotypic Plasticity Promotes Ecological Speciation in Postglacial Lakes

The salmonid arctic charr Salvelinus alpinus (L.) is one of the most widespread fishes in the world and is found farther north than any other freshwater or diadromous fish, but also in cool water farther south. It shows a strong phenotypic, ecological, and life history diversity throughout its circumpolar range. One particular side of this diversity is the frequent occurrence of two or more distinct charr morphs in the same lake. This polymorphism has been termed ‘the charr problem’. Similar cases are found in other postglacial fishes, but not with the extent and diversity as with the arctic charr. This review first treats the classical case, pioneered in an advanced way by Winifred Frost, of autumn and winter spawning charr in Windermere, England, and three other cases that have received much research interest in recent years: Thingvallavatn, Iceland; Loch Rannoch, Scotland; and Fjellfrøsvatn, Norway. Then a special kind of sympatry with one morph living permanently in the profundal zone, known from a few lakes in Europe, Russia and Canada and unique for arctic charr among postglacial fishes, is reviewed. Among them is a recently discovered charr at 450 m depth in Tinnsjøen, Norway, one of the few very deep lakes in the world. With examples, the concluding discussion focuses on the variation of arctic charr polymorphisms which extends from early stages of ecological segregation to cases of reproductive isolation and speciation; and on models to explain the charr problem. The exceptional diversity of arctic charr provides a unique potential for further progress in studies on ecologically driven evolution within the frames of modern theory of developmental plasticity, adaptive radiation and adaptive speciation.

The Charr Problem Revisited: Exceptional Phenotypic Plasticity Promotes Ecological Speciation in Postglacial Lakes

Abstract The salmonid arctic charr Salvelinus alpinus (L.) is one of the most widespread fishes in the world and is found farther north than any other freshwater or diadromous fish, but also in cool water farther south. It shows a strong phenotypic, ecological, and life history diversity throughout its circumpolar range. One particular side of this diversity is the frequent occurrence of two or more distinct charr morphs in the same lake. This polymorphism has been termed ‘the charr problem’. Similar cases are found in other postglacial fishes, but not with the extent and diversity as with the arctic charr. This review first treats the classical case, pioneered in an advanced way by Winifred Frost, of autumn and winter spawning charr in Windermere, England, and three other cases that have received much research interest in recent years: Thingvallavatn, Iceland; Loch Rannoch, Scotland; and Fjellfrosvatn, Norway. Then a special kind of sympatry with one morph living permanently in the profundal zone, known ...

The study of intra-specific growth variability of Illex argentinus (Cephalopoda: Teuthida) in Brazilian waters as reconstructed from the gladius microstructure

Intra-specific growth variability of the gladius of Illex argentinus was analyzed based on 870 specimens collected off Brazil from 2001 to 2002, and divided into two depth groups (shelf break and slope spawners) between 23–32°S and depths of 45–722 m. Squid samples included adult individuals caught throughout the year and were pooled by sex and season (spring, summer, autumn and winter spawners). Growth increments measured directly on the gladius plate were smoothed by a low-pass filter and used to reconstruct size-specific growth trajectories for males and females separately. The reconstructed trajectories of the proposed spawning groups were found to be significantly different. Squid captured during the winter exhibited faster growth followed by summer, spring and autumn spawners. During winter, shelf-break spawners presented lower growth rates when compared to slope spawners. Seasonal and bathymetric growth variability was discussed in the light of biological production patterns off southeastern and southern Brazilian coast. Higher growth rates observed in the trajectories reconstructed for winter spawners could not be supported by these local patterns and it is suggested that they reflect an early-life in more productive areas, such as the Patagonian shelf.

Changes in Sperm Production, Sperm Motility, and Composition of Seminal Fluid in Caspian Brown Trout, Salmo trutta caspius, Over the Course of a Spawning Season

This study was carried out to evaluate milt quality in male Caspian brown trout (Salmo trutta caspius) over the course of the winter spawning season. Milt samples were collected biweekly during December and January. Chemical composition of seminal fluid, sperm production (milt volume, sperm density, spermatocrit,) and sperm motility characteristics (percentage and duration of motility) were measured. Milt volume, sperm density, osmolality, seminal minerals (Ca2+, Mg2+, K+, Na+, Cl−), and total protein gradually decreased over the spawning season. Glucose and triglyceride content of milt did not show significant changes over the spawning season. Milt pH and the percentage and duration of motility were comparatively stable, declining only at the end of the season. Significant positive correlations were found between sperm density and seminal minerals, total protein and spermatocrit; percentage of motile spermatozoa and seminal minerals, total protein; and duration of motility and K+, Cl−, total protein, and pH. Results show that season has a significant influence on milt quality in male Caspian brown trout, with the best milt being available at the beginning of spawning season.

The Spawning Run of Blueback Herring in the St. Johns River, Florida

AbstractBlueback herring Alosa aestivalis are anadromous, iteroparous, winter spawners in the St. Johns River, Florida, but published data about this population are limited. We collected adults by electrofishing in the upper St. Johns River during the 2002–2005 spawning runs to examine the abundance, distribution, size, sex ratio, reproductive biology, and feeding habits of the population. When possible, data from the present study were compared with those for blueback herring collected with seine nets in the lower St. Johns River during the 1972 and 1973 spawning runs. Blueback herring began upstream migration by January and stayed in the river until at least April. The average fish size was significantly smaller in 2002–2005 than in 1972–1973, but sex ratios were not different from 1:1 in 5 of the 6 years studied. The more recent collections suggest that blueback herring females released multiple batches of eggs during one spawning season (spawning a batch every 3–4 d on average) and that spawning occurred as far upstream as river kilometer 400. Males and females fed actively during the entire spawning run. Overall, the stock is persistent, but its status is unknown and the smaller individual sizes evident today suggest that this population is experiencing higher mortality now than a few decades ago.

Fecundity, atresia, and spawning strategies of Atlantic herring (Clupea harengus)

Atlantic herring ( Clupea harengus ) have contrasting spawning strategies, with apparently genetically similar fish “choosing” different spawning seasons, different egg sizes, and different spawning areas. In the North Sea, both autumn- and winter-spawning herring share the same summer feeding area but have different spawning areas. Females of both spawning types start their oocyte development in April–May. Oocyte development is influenced by the body energy content; during the maturation cycle, fecundity is down-regulated through atresia in relation to the actual body condition. Hence, fecundity estimates must account for the relative time of sampling. The down-regulation over the whole maturation period is approximately 20% in autumn- and 50% in winter-spawning herring. The development of the oocytes is the same for both spawning strategies until autumn when autumn spawners spawn a larger number of small eggs. In winter spawners, oocyte development and down-regulation of fecundity continues, resulting in larger eggs and lower number spawned. In theory, autumn and winter spawners could therefore switch spawning strategies, indicating a high level of reproductive plasticity.

Temporal trends in stock origin and abundance of juvenile herring (Clupea harengus) in the Irish Sea

Abstract Burke, N., Brophy, D., Schön, P-J., and King, P. A. 2009. Temporal trends in stock origin and abundance of juvenile herring (Clupea harengus) in the Irish Sea. – ICES Journal of Marine Science, 66: 1749–1753. Celtic Sea herring (Clupea harengus) larvae partly disperse into the Irish Sea, where they mix with the resident stock during their first year of life. This affects the reliability of the use of acoustic estimates of juvenile abundance on the Irish Sea nursery grounds as a recruitment index for use in stock predictions. Otolith microstructure analysis can be used to distinguish between autumn-spawned and winter-spawned individuals. Because winter spawners do not occur in the Irish Sea, this component can be assigned to Celtic Sea immigrants. We used this method to estimate the proportion of winter-spawned individuals in samples of age-1 herring from the western Irish Sea over a 10-year period (1993–2003), and subtracted a corresponding proportion from the acoustic age-1 abundance estimates. The adjusted index for autumn-spawned (supposedly Irish Sea) juveniles was significantly correlated with the abundance of age-3 fish from the same year class in commercial catches and in the acoustic surveys (p < 0.05 and <0.01, respectively), whereas the correlations for unadjusted indices were not significant. These findings are discussed in relation to the monitoring and assessment of herring in the two areas.

Schooling pattern of eastern Bering Sea walleye pollock and its effect on fishing behaviour

Abstract Shen, H., Dorn, M. W., Wespestad, V., and Quinn, T. J. 2009. Schooling pattern of eastern Bering Sea walleye pollock and its effect on fishing behaviour. – ICES Journal of Marine Science, 66: 1284–1288 Walleye pollock (Theragra chalcogramma) form persistent midwater and near-bottom schools in the daytime during the winter spawning season in the eastern Bering Sea (EBS). Two spawning areas in the EBS, north of Unimak Island and near the Pribilof Islands, are the main fishing grounds. To study the schooling pattern of pollock and its effect on fishing behaviour on these two fishing grounds, a principal component analysis with instrumental variables was carried out using acoustic and observer data from 2003 and 2005. Significant differences between the school descriptors distinguished the schooling patterns among areas and years. The harvester, that is to say, the fishing vessel and its crew taken together, searched for fish aggregations, which were caught in a different manner when the schooling pattern changed. School density had a greater effect than school size on fishing behaviour. Aggregations were less dense in 2003 than in 2005, and the harvester tended to fish with longer tows, at higher speeds, when it encountered less dense aggregations.

Reproduction in the sea pen Funiculina quadrangularis (Anthozoa: Pennatulacea) from the west coast of Scotland

The sea pen Funiculina quadrangularis (Pallas, 1766) is a species of conservation concern in Scottish coastal waters, due to its restricted geographical distribution and high sensitivity to demersal fishing activities. Reproduction in F. quadrangularis was investigated in a population located in southern Loch Linnhe, west Scotland. This was accomplished through the analysis of trends in oocyte size-frequency distribution and relative fecundity over a 12-month period. Funiculina quadrangularis is dioecious and the study population exhibited a sex ratio of 1:1. Oogenesis in female F. quadrangularis is characterised by the maintenance of a large pool of asynchronously developing oocytes throughout the year, of which a small proportion (<10%) mature with increasing sychronicity and are spawned in midwinter. The reasons for this distinct pattern of oogenesis and winter spawning remain unclear, although the potential influence of environmental cues and the role of endogenous factors in relation to this sea pen's deep-sea habit are discussed. Whilst the duration of oogenesis is prolonged (>12 months), it is proposed that spawning is a brief and synchronous annual event. Relative fecundity is high and is independent of colony size, varying between approximately 500–2000 oocytes per 1 cm rachial midsection. This measure of fecundity exhibited pronounced seasonality and was significantly lower during the post-spawning winter months. Total fecundity in F. quadrangularis is considered to be high; although a small proportion of the total number of oocytes is spawned annually, this is compensated for by large colony size. Funiculina quadrangularis produces large oocytes (>800 μm), indicative of the production of lecithotrophic larvae.

The Reproductive Cycle of the Scallop Pecten sulcicostatus from the Southern Benguela Upwelling System

The reproductive cycle of Pecten sulcicostatus is described as part of an investigation into the potential commercial culture of this species in South Africa. Scallops were collected monthly from False Bay, from August 2004 to October 2005, to determine seasonal variation in the gonadosomatic index (GSI) and to assess associated histological changes within the gonads. The reproductive cycle of P. sulcicostatus demonstrated clear seasonality. The mean GSI was highest from June to September (winter to early spring), and lowest from November to January (late spring to summer). The GSI findings were corroborated by histological analysis of the gonads with the mean oocyte diameter reaching a maximum in August and a minimum in November. Seasonal stratification and corresponding changes in phytoplankton biomass are considered to control the reproductive cycle of P. sulcicostatus in False Bay as winter spawning and the subsequent decline in the GSI coincide with the transition to spring upwelling conditions and a decline in bottom water temperature and food availability.

Distinct migratory and non-migratory ecotypes of an endemic New Zealand eleotrid (Gobiomorphus cotidianus) – implications for incipient speciation in island freshwater fish species

BackgroundMany postglacial lakes contain fish species with distinct ecomorphs. Similar evolutionary scenarios might be acting on evolutionarily young fish communities in lakes of remote islands. One process that drives diversification in island freshwater fish species is the colonization of depauperate freshwater environments by diadromous (migratory) taxa, which secondarily lose their migratory behaviour. The loss of migration limits dispersal and gene flow between distant populations, and, therefore, is expected to facilitate local morphological and genetic differentiation. To date, most studies have focused on interspecific relationships among migratory species and their non-migratory sister taxa. We hypothesize that the loss of migration facilitates intraspecific morphological, behavioural, and genetic differentiation between migratory and non-migratory populations of facultatively diadromous taxa, and, hence, incipient speciation of island freshwater fish species.ResultsMicrochemical analyses of otolith isotopes (88Sr, 137Ba and 43Ca) differentiated migratory and non-migratory stocks of the New Zealand endemic Gobiomorphus cotidianus McDowall (Eleotridae). Samples were taken from two rivers, one lake and two geographically-separated outgroup locations. Meristic analyses of oculoscapular lateral line canals documented a gradual reduction of these structures in the non-migratory populations. Amplified fragment length polymorphism (AFLP) fingerprints revealed considerable genetic isolation between migratory and non-migratory populations. Temporal differences in reproductive timing (migratory = winter spawners, non-migratory = summer spawners; as inferred from gonadosomatic indices) provide a prezygotic reproductive isolation mechanism between the two ecotypes.ConclusionThis study provides a holistic look at the role of diadromy in incipient speciation of island freshwater fish species. All four analytical approaches (otolith microchemistry, morphology, spawning timing, population genetics) yield congruent results, and provide clear and independent evidence for the existence of distinct migratory and non-migratory ecotypes within a river in a geographically confined range. The morphological changes within the non-migratory populations parallel interspecific patterns observed in all non-migratory New Zealand endemic Gobiomorphus species and other derived gobiid taxa, a pattern suggesting parallel evolution. This study indicates, for the first time, that distinct ecotypes of island freshwater fish species may be formed as a consequence of loss of migration and subsequent diversification. Therefore, if reproductive isolation persists, these processes may provide a mechanism to facilitate speciation.