The alien false limpet (Siphonaria pectinata) in the Bizerte channel (northern Tunisia): spawning,development and growth under laboratory conditions

Spawning, development and growth of Siphonaria pectinata in the laboratory were studied and described in detail during a one-year study period. Egg ribbons were observed in February, March, April, June, July, August and September, with a peak in number of ribbons per individual in July. On average, individuals laid 9.0 ± 5.1 egg ribbons at a spawning frequency of one egg ribbon day^?1. The number of eggs per ribbon ranged from 752 to 50,400 depending on ribbon length. Embryonic development studied in February (13–15 °C), April (15–17 °C) and July (25–27 °C), reached hatching within 8–16 days with average larval lengths of 76.7 ± 5.9, 83.0 ± 11.3 and 78.3 ± 9.0 μm, respectively. Massive mortality was registered a few days after hatching, with larval longevity depending on the study period. Larval settlement occurred within 36–38 days after hatching, but only in the spawn deposited in February. Larval growth was slow during the first three weeks (18–26 μm week^?1) and then accelerated until the sixth week (40–67 μm week^?1). The present study contributes knowledge on the spawning, development and growth of S. pectinata, an alien species recently spreading throughout the Tunisian coast.     

THE ECOLOGY OF THE HONG KONG LIMPETS CELLANA GRATA (GOULD 1859) AND PATELLOIDA PYGMAEA (DUNKER 1860): REPRODUCTIVE BIOLOGY

Cellana grata is large, relatively long lived (3 years), withone winter breeding season each year which can be correlatedwith major seasonal climatic and hydro-logical events, e.g.,winter reduction in temperature and higher seas. C. grata ischaracterised by a relatively low value of mean annual reproductiveeffort (males: 23%; females: 18%). Patelloida pygmaea is small,short lived (1 year), with one spring breeding season each yearand devotes a large proportion of metabolic energy for reproduction.P. pygmaea showed a higher value of mean annual reproductiveeffort (males: 46%; females: 31%) than C. grata. Mature gonads of Cellana grata first appeared in June and itreached a peak maturity (100%) in September, remaining so untilDecember, i.e., the maturation of the gonads coincided withincreasing water temperatures, with spawning associated witha decrease in water temperature. Gonadal development by Patelloidapygmaea began in either July or August and reached a peak inDecember, remaining so until a major peak in spawning took placebetween April and May, i.e., gonad maturation coincided witha decline in water temperature, with spawning following thesubsequent increase. Limpet gonadal cycles are likely gearedto temperature and food supply. Spawning occurred between Novemberand December, when wave heights are typically 1 m higher thanin summer. (Received 1 December 1992; accepted 25 June 1993)     

The Potential of Two Perennial C4 Grasses and a Perennial C4 Sedge as Ligno-cellulosic Fuel Crops in N.W. Europe. Crop Establishment and Yields in E. England

Three perennial C₄ rhizomatous species, Cyperus longus L., Spartinacynosuroides and Spartina pectinata Link, were examined as potentialrenewable energy crops. These species are unusual among C₄ plantsin showing natural distributions which extend into cool temperateregions. This study examined whether these species could beestablished in the cool temperate climate of eastern Englandand whether they could consistently attain the relatively highdry matter yields associated with C₄ plants of warmer regions.Clonally produced material was planted in 1986, on two siteswith contrasting soil types in Essex, eastern England. Plantingwas within a randomized-block design incorporating replicatedplots of each species, both with and without fertilizer. Survivorshipand stem demography were monitored at monthly intervals from1986 to Jun. 1989 for stem recruitment and to Dec. 1991 forstem density. Yields were determined from 1987 (the year followingestablishment) to 1993. Survivorship of the planted propagules over the first 12 monthswas 92% for S. pectinata , 96% for S. cynosuroides and 100%for C. longus. Recruitment of new stems peaked in Apr. of mostyears, although a significant number of new stems appeared asearly as Feb. Stem death peaked in Sep. or early Oct. and allabove-ground stems had died by mid-Nov. Stem density trendsindicated that 2-4 years were required to reach a steady-statedensity, depending upon species. The stem density of the twoSpartina species had reached more than 1000 m^-2 in 1989 althoughthat of S. pectinata fluctuated considerably in the subsequentyears. C. longus stem density rose to approx. 600 m^-2 by 1988and did not change significantly in the subsequent years. In the 6 years following establishment, annual yields averagedacross all fertilizer treatments and both sites were 1·0,1·1 and 1·3 kg m^-2 for C. longus, S. cynosuroidesand S. pectinata, respectively. The average annual yield ofall three species at the site with the heavier soil was 1·3kg m^-2. This was significantly greater than the 1·0 kgm^-2 on the lighter soil. Nitrogen addition did not significantlyincrease yield. Even in the absence of any nitrogen addition,the annual yield of S. pectinata averaged 1·2 kg m^-2over the 6 years, with no evidence of any decline with the increasingage of the stands.Copyright 1995, 1999 Academic Press Cyperus longus, Spartina cynosuroides, Spartina pectinata, energy crop, dry matter yield     

ADAPTATIONS FOR COLD WATER SPAWNING IN LOLIGINID SQUID: LOLIGO GAHI IN FALKLAND WATERS

Inshore spawning sites of the cold water squid Loligo gahiwere found in the waters of East Falkland (Southwest Atlantic),where there is a major fishery based on this species. Egg massesoccurred in algal beds, often at the outer (seaward) edge, with ambientwater temperatures of 6.5-90C and salinity 33.75- 33.58. They wereattached to the stipes of the kelp algae Lessonia spp. and Macrocystispyrifera from 0.5 m to 2.5 m off the bottom at 8-20 m depths.The overall density of egg masses was low. The egg mass is abundle of elongated gelatinous translucent capsules with eachcapsule firmly attached to the kelp stipe at its basal end.The capsules are mainly 50-60 mm in length and contain an averageof 70 fertilized eggs. Sampled egg masses consisted of 4-161 capsulesand from 138 to 11,487 eggs. Large egg masses (. 50 capsules) wereapparently formed by several females at different times, as embryosin different capsules were at various stages of development.Eggs laid in winter are significantly larger than those laidin summer. In comparison with tropical and temperate Loligo spp.L. gahi have short egg capsules containing a small number of eggs,but the eggs (2.2-2.5 mm diameter) and hatchlings (3.1-3.4 mm mantlelength) are large. These are probable adaptations for cold waterspawning and development. (Received 30 March 2000; accepted 5 June 2000)     

Environmental and Endocrine Influences on Reproduction of Fundulus heteroclitus

Reproduction in Fundulus heteroclitus is adapted to the temperateclimate and the tidal environment of the coastal marshes whichare its primary habitat. Egg deposition and spawning are closelylinked to the tidal cycle. Concentration of spawning on springtides gives the fish access to sites in the high intertidalzone. Eggs are deposited near the high water mark, usually insand in New England populations and in Spartina alternifloraor empty Geukensia demissa shells in Middle Atlantic and southernpopulations. Aerial incubation of eggs appears to be essentialfor their survival in the salt marsh. Loss of eggs due to lackof fertilization, mortality during development and predationwas always less than 30 percent in our observations. Hatchingoccurs only when the eggs are inundated, usually on spring tides.An endogenous semilunar gonadal cycle appears to be involvedin control of spawning, but an effective environmental synchronizerhas not been found. Cyclic changes in estradiol-17ßaccompany the gonadal cycle, while spawning behavior is stimulatedby neurohypophyseal hormones. Both temperature and photoperiodhave been implicated in the control of seasonal reproductionin F. heteroclitus. Early workers focused on males and concludedthat increasing temperature was the stimulus that initiatedgonadal recrudescence in spring. These experiments were notrigorous tests of the effects of photoperiod. We have shownthat in females both warm temperatures and long photoperiodsare involved. In female F. heteroclitus, as in most mammalsand birds, it is the timing rather than the duration of thelight exposure which determines its effectiveness in stimulatinggonadal maturation. Maintenance of gonadal maturity in femaleF. heteroclitus depends on long photoperiods, but the ovarymay become refractory and regress even when stimulatory photoperiodsare sustained in the laboratory. Ovarian maturity can be stimulatedwith gonadotropin injection in refractory animals, indicatingthat the brain-pituitary axis is the site of refractoriness.The pathway by which light influences ovarian maturity may involvean encephalic photoreceptor, since neither the eyes nor thepineal gland is necessary.     

A Suite of Adaptations for Intertidal Spawning

Salt marshes and similar tide-dominated habitats present anunusual challenge for reproduction of resident aquatic organisms.Strong currents, siltation and hypoxia can potentially contributeto reproductive failure through mortality of the eggs or flushingof the eggs and larvae from the habitat. Fundulus heteroclitus,a small brackish water killifish, is a common resident of tidalmarshes along the east coast of North America from Newfoundlandto Florida. The reproductive strategy of this and related speciesis based on aerial incubation of eggs in the high intertidalzone. The eggs are resistant to desiccation and, when fullydeveloped, hatch on immersion. Copulatory behavior and anatomyof accessory reproductive structures are adapted to placementof eggs in protected incubation sites. The gonads of both malesand females mature rhythmically with an endogenous circasemilunarperiod, which is synchronized with the "spring" tides of newand full moons. Spawning occurs on high tides. Embryos developin 9–15 days, and usually hatch on the succeeding springtide series. Reproductive cyclicity in F. heteroclitus and relatedfishes ensures that spawning fish will have access to the highintertidal zone, thereby permitting aerial incubation of eggs.     

A Quantitative Study of Environmental Factors Influencing the Seasonal Onset of Reproductive Behaviour in the South American Apple-snail Pomacea canaliculata (Gastropoda: Ampullariidae)

Two laboratory experiments were carried out on sets of winter(inactive) pairs of Pomacea canaliculata (Lamarck), one to studythe influence of water temperature (either 18°C or 25°C,corresponding to late winter and summer temperatures in Mendoza, respectively)and day length (either 10 h light/day or 14 h light/day, correspondingto the shortest and the longest day of the year in Mendoza,respectively), and the other to determine the effects of foodavailability (ad libitum feeding vs. restriction to 25% of thead libitum requirements) on the frequency of copulation andspawning, on spawn measurements (number and volume of eggs,and spawn volume), and on an index of the reproductive effort.Animals in all experimental groups were observed during 4 weeks,after seven days of acclimation to the experimental aquaria(under low water temperature and short photoperiod). Low watertemperatures induced a lesser and later activation of copulationand spawning than that induced by warm temperatures. Day lengthwas without effect on both behaviours. Both the frequency ofspawning and the reproductive effort index decreased under restrictedfeeding, without altering the spawn measurements. The latencyperiods for both copulatory and spawning behaviours were similarin both ad libitum and restrictedly fed groups. We concludethat water temperature may be the critical factor that causesthe seasonal onset of copulatory and spawning behaviour in theseapple-snails. However, food availability may also be a determiningfactor, mainly to trigger spawning activity. These results suggestthat the factors that control the seasonal onset of the sexualactivities in Pomacea canaliculata are similar to those thatcontrol the seasonal arrest, thereby establishing the annualpattern of reproduction in this species. (Received 26 January 1998; accepted 23 July 1998)     

VARIATIONS IN INFESTATIONS OF SIPHONARIA CAPENSIS AND S. CONCINNA(PULMONATA) BY LARVAL TREMATODES IN SOUTHERN AFRICA

The prevalence of digenean trematode parasites in Siphonariacapensis (Pulmonata) was examined in populations from 24 sites,and in S. concinna from 10 sites along the coast of southernAfrica from 1989 to 1991. Sporocysts containing cercariae werefound in the digestive gland of both species. To date, two typesof cercaria have been isolated from S. capensis and one typefrom S. concinna, these types possibly representing three distinctspecies of trematode. In approximately 30% of parasitized S.capensis and 10% of parasitized S. concinna the digestive glandwas completely destroyed. In both species of Siphonaria therewas considerable temporal and spatial variation in parasiteprevalence. At some locations up to 40% of S. capensis wereinfected whereas at others, no parasites were found. Prevalenceof trema-todes in S. concinna rarely exceeded 12%. At severalsites the prevalence of infestation within the limpets increasedwith increasing host size. (Received 8 June 1992; accepted 6 July 1992)     

Reproductive biology of the East African lungfish (Protopterus aethiopicus) in Mwanza Gulf, Lake Victoria

The population of lungfish (Protopterus aethiopicus (Heckel)) was sampled by bottom trawling for 12 months from June 1984 to May 1985. A total of 576 lungfish were investigated. The sex ratio in the population was 1 male : 1 -98 females. Average size at maturity was found to be 960cm total length (TL) but the smallest matured male measured 72-9 cm and the female 840 cm TL. It was not possible to establish spawning times and reproductive activity trends either from the variation in relative condition factor ‘kn’ or from gonadosomatic index (GSI). Whereas male lungfish seem to show no further increase in GSI after gonadal maturity stage III, females exhibit GSI values that vary directly with oocyte maturation and ovarian weights. Fat deposited along the gonads was found to be a better basis for assessing maturation and spawning in lungfish. The potential spawning period was found to be from September to May. Absence of lungfish with spent gonads over the 12-month period and the presence of different egg sizes in ovaries, suggest that the fish is a multiple spawner. Fecundity was found to range from 705 eggs (in 84-cm TL fish) to 14,922 eggs (in 130-cm TL Fish).     

PATTERNS OF REPRODUCTION IN THREE SANDY BEACH WHELKS OF THE GENUS BULLIA GRIFFITH

The breeding cycles of two species of sandy beach whelk (Bulliadigitalis and B. pura) are presented and compared with a thirdspecies (B. rhodostoma). In all three species, egg maturationand copulation occur in spring while summer marks the depositionand spawning of egg capsules. B. digitalis and B. pura migrateoffshore to lay their eggs, the juveniles of both species restrictingthemselves to beyond the breaker zone. Newly hatched snailsof B. rhodostoma appear in the intertidal towards late summer.The discovery of a penis-like structure on females of B. rhodostomais investigated. The pseudopenis was also found on B. pura butnever on B. digitalis. The possibility of a sex-change was eliminatedon the histological investigation of the gonads of a range ofsnails and the examination of sex-ratios over a period of fivemonths. General trends in reproductive behaviour are also discussed. (Received 18 March 1984;     

Variations of lipid and fatty acid contents during the reproductive cycle of the anthozoan <Emphasis Type="Italic">Renilla koellikeri</Emphasis>

Lipid and fatty acid contents were monitored in the sea pansy Renilla koellikeri during its reproductive cycle. The fluctuations of lipids and fatty acids were closely related to sexual development and gonads represented the principal site of lipid storage in the colony. Between April and May, fatty acids and lipids greatly accumulated just prior to spawning. The subsequent decrease of lipid and fatty acid contents in June probably resulted from loss due to spawning. Fatty acid composition was assessed for the whole animal and was compared between male and female gonads, and between gonads and somatic tissues. Arachidonic acid (AA) was the principal fatty acid in the whole colony followed by palmitic acid and eicosapentaenoic acid (EPA). The examination of fatty acid variations in gonads showed that EPA and AA were highly incorporated in eggs during the month preceding spawning, whereas in the same period, EPA was the only fatty acid to accumulate in spermatophores. The differences of fatty acid levels observed in gonads reflected sex differences observed in colonies. The seasonal variations of the omega6/omega3 ratio of the colonies were largely influenced by EPA and AA, and appeared as a reliable indicator of the sexual maturity of the sea pansy.     

SPAWNING SEASON AND EGG PRODUCTION IN FORTH ESTUARY RETUSA OBTUSA (MONTAGU) (GASTROPODA: OPISTHOBRANCHIA)

Retusa obtusa held individually in the laboratory carried largeoocytes in the gonad but did not spawn in December-late January.In late Jan-early Feb, however, the first few individuals producedbatches of 8–17 eggs and, by early February, most individualswere producing means of 2–4 eggs d^–1 and maximain late Feb of <7.9 d^–1. Spawning declined to low levelsin few individuals in late March. By early April, spawning hadvirtually ceased prior to the drastic loss of adults in thepopulation by May. Larger R. obtusa generally produced more eggs than smaller onesand the few specimens shorter than 3.8 mm produced markedlyfewer than those of 3.8–5.0 mm shell length. Twenty of the 34 R. obtusa held in the main breeding period(4 sets started 29 Jan-3 Mar) spawned in 3 or more successiveweeks whereas only 6 of them failed to spawn in 2 consecutiveweeks, so indicating that several successive batches of eggsare commonly produced. Yet in virtually all individuals (exceptat the start of breeding) more eggs were produced in the firstweek of captivity than subsequently. These first-week valuesimply total production by individuals in the spawning seasonof some 112-305 eggs comprising about 2.8-7.6 mg dry weightor, by the Forth estuary population, of 26880-73200 eggs m^–2comprising 0.67-1.83 g dry weight m^–2. (Received 19 August 1988; accepted 30 September 1988)     

Gonad maturation and spawning of cobia,Rachycentron canadum (Linnaeus, 1766) off the Dungun coast,Malaysia

The reproductive biology of cobia, Rachycentron canadum, from the coastal waters of Dungun, Malaysia was studied from June 2014 to May 2015. From commercial trawls, a total of 201 samples (combined sexes) were collected (fork lengths [FL] 37.5–124.0 cm; body weights 0.5–20.4 g). The overall sex ratio of females to males was 1:0.9, which was not significantly different (χ² = 2.12, df = 1; p < .05). Estimations of length at 50% maturity (L₅₀) showed that both sexes matured at approximately 75 cm FL; estimated spawning frequency was 6 days. Mean batch fecundity (BF) ranged from 0.55 to 4.32 million eggs. The average number of eggs per gram of ovary was from 2,100 to 5,400 eggs, and relative fecundity 147 eggs/g. There was a weak positive correlation (r² = .48) between BF and female FL as well as BF with an ovary‐free body weight (r² = .56), possibly due to females being in a continuous spawning condition and some possibly half‐spent, based on the histological examination of the female gonads. Despite cobia being asynchronous spawners, the gonadosomatic index in both males and females showed peaks in June, November, and particularly March. Based on histological examination, spawning‐capable males were encountered throughout the study period, whereas spawning‐capable females in the late developing subphase were found mostly in March and April. This is the first study on the reproductive aspects of cobia in Malaysian waters.     

Environmental and physiological controls on shell microgrowth pattern of Ruditapes philippinarum (Bivalvia: Veneridae) from Japan

The reproductive cycle and shell microgrowth patterns of thevenerid bivalve Ruditapes philippinarum from Matsukawa-ura,a small inlet facing the Pacific Ocean, northeastern Japan wereexamined. Histological examination of the gonads revealed thatspawning in this species occurred twice in 2005, once betweenlate June and early August and the other between late Septemberand early October. Comparison of the shell microgrowth patternswith the developmental stages of the gonad in each individualrevealed that in spawning individuals (mature and spawning stages),the mean lunar-day growth rates were significantly smaller thanthose in individuals which were not in spawning condition (spent,recovery and growing stages). In non-spawning individuals, themean lunar-day growth rates were positively correlated withseawater temperature up to 20°C. However, in spawning individuals,no correlation was observed between shell growth and seawatertemperatures >16°C. These facts suggest that physiologicalstress during reproduction has a negative influence on shellgrowth and results in spawning breaks. The present study indicatethat spawning breaks can be used to identify the timing of sexualmaturity and to count the number of spawning events occurringper year in extant and fossil bivalves.     

Chemosensory cues attract lake trout Salvelinus namaycush and an egg predator to the spawning substratum

A field experiment was conducted to determine whether chemosensory cues emanating from lake trout Salvelinus namaycush spawning substratum attract breeding S. namaycush. Substrata from either a spawning site or a control site were randomly placed in trap nets around an isolated spawning shoal; those containing spawning substratum caught significantly more S. namaycush, as well as a greater proportion in breeding condition. White sucker Catostomus commersoni were a major predator of S. namaycush eggs and were also captured in greater numbers in nets with spawning substratum.     

Individual Spawning Duration of Captive Atlantic Bluefin Tuna (Thunnus thynnus) Revealed by Mitochondrial DNA Analysis of Eggs

This study presents the first results on Atlantic bluefin tuna (Thunnus thynnus) individual spawning duration and its short-term temporal behavior. The study was based on direct measurements resulting from mtDNA analysis of the offspring of spawners held in transport cages during the 2013 spawning monitoring survey in Balearic waters. The number of females consisted of approximately 259 individuals with an average weight of 186 kg. The survey began on May 22 and ended on July 3. Spawning started on May 30 and was observed every night afterwards. The sampling of eggs for genetic monitoring was conducted for 9 days interspersed from the beginning of spawning to the end of the survey. A total of 946 eggs were analyzed and revealed 129 different haplotypes; 77 of these were not previously detected in the Mediterranean. A total of 69 haplotypes were observed in more than one spawning event and those with higher frequency lasted their maximum possible duration. The haplotypes present at the beginning of spawning were also identified at the end of the sampling, indicating a minimum spawning duration of 34 days, and individual annual fecundity was estimated at around 1290 eggs gr^-1. These results differed from those generally presumed until now and are indicative of a much higher fecundity. Females exhibited a regular spawning schedule but with the capacity to shift the spawning hour during the spawning season. These results were observed for the eastern population of Atlantic bluefin tuna and before extrapolating to the western population, their validity should be proved.     

INTER-YEAR CONTRAST IN NUMBERS AND ANNUAL PRODUCTION OF THE CEPHALASPIDEAN OPISTHOBRANCH RETUSA OBTUSA (MONTAGU) AND THE POSSIBLE INFLUENCE OF WIND-SPEED

Retusa obtusa was far more abundant throughout August 1986-July1987 than in all 12 corresponding months of April 1992-March1993. The greatest difference was when the highest of all counts(3232 m^-2) in May 1987 was 18-times that in May 1992. The leastdifference was a 2.4-fold discrepancy between the two Septembercounts. Mean monthly counts for the 2 periods were 781.4 m^-2(1986-87) and 123.6 (1992-93): a difference of 6.3-times. Biomasssimilarly differed between the 2 periods by factors between2.5 (July) and 12 (March), with a 5.3-fold difference betweenmean monthly biomass values. Annual production was accordinglyestimated as 618.3 (1986-87) and 152.4 (1992-93) mg AFDW m^-2y^-1; so differing by a factor of 4. Yet, in both these 1-yearperiods of observation, the general pattern of annual changewas the same, with settlement in February-May, growth from springto winter, most spawning in December-March and death of adultsat about 1 year in April-May. It is likely that the winter-springperiod of early development in benthic eggs followed by pelagicdispersal, and then settlement in February -May, is a periodof especial vulnerability. In particular, it seems likely thatduring January-May, markedly higher wind-speeds in 1992 thanin 1987 might have contributed to the huge difference in numbersof recruits (Received 2 February 1994; accepted 18 March 1994)     

Spatial distribution of small pelagic fish larvae in the Gulf of California and its relation to the El Nino 1997-1998

Sardinops caeruleus larvae were almost absent during the ElNiño 1997–1998, when the sea surface temperature(SST) increased by 4°C. After the event, these larvae appearedin high abundance between 18 and 22°C SST. Engraulis mordaxlarvae were recorded in high abundance during the El Niño(17 and 25°C SST) and afterwards (14 and 22°C). Duringthe event, they tended to concentrate close to Isla Angel deLa Guarda and Isla Tiburón, the coldest zone. The ElNiño conditions affected the spawning of S.caeruleusmore than E.mordax, with the latter more adapted to strong environmentalchanges.     

Sexual reproduction of the reef-building coral Diploria labyrinthiformis (Scleractinia: Faviidae), in the Colombian Caribbean

Sexual reproduction of the coral Diploria labyrinthiformis was studied for the first time. Monthly histological analyses at the Corales del Rosario National Park (Colombian Caribbean) from May 1997 to April 1998 show that D. labyrinthiformis is a hermaphroditic broadcasting species. It presents an annual gametogenic cycle with a 10-11 month period for gonad investment, in which oogenesis begins in August and ends in May-June. Spermiogenesis is short because sperm cysts were only observed in May tissue samples. In histological collected in May, an average of four mature eggs and six spermatic cysts per fertile mesentery were found. The mean diameter of mature eggs was 297 microm (+/- 97 SD) and 90 microm (+/- 33) for spermatic cysts. Rapid maturation of eggs from stage II to stage III coincides with increases in air temperature, high number of solar hours per month, decreases in wind velocity and absence of rainfall. Reproductive effort for D. labyrinthiformis (14.07 mm3/cm2/year) was similar to other Faviidae species. Although gamete release was not observed in the field, the absence of gonads in histological samples in June suggests spawning between May 25 (five days after full moon) and June 24. This event coincides with high air temperature, low number of solar hours per month, low wind velocity, and initiation of the rainy season. The earlier spawning time of this species differs from other species of the same family known for the Caribbean region.