Assessment of the Feasibility of Preventing Reproduction of Lake Charr, Salvelinus Namaycush, in Shallow Areas of Reservoirs Affected by Drawdowns

Lake charr, Salvelinus namaycush, spawn almost exclusively in lakes, in the fall. Spawning sites in inland lakes are generally located close to the shore in areas with coarse-textured substrate, and in depths of less than 2m. Because of the type of water management system applied in reservoirs where water levels are lowered during the winter, eggs deposited during the fall around the shallow shoreline of reservoirs can be exposed. The depth of spawning sites relative to drawdowns may be a limiting factor for lake charr survival in reservoirs. In 1995 and 1996, we evaluated the ability to induce lake charr reproduction in deeper water, below the range of fluctuating water levels by the sequential construction of artificial reefs and limiting access to natural spawning habitat. The creation of artificial deeper water spawning areas, adjacent to natural sites, produced a partial transfer of reproduction. However when natural spawning sites were covered with tarpaulins almost all the eggs were laid in the artificial deeper water spawning areas. Complete or partial transfer of reproduction activities to sites below the depth not affected by water level fluctuations is therefore a potential way of alleviating the effects of hydroelectric reservoir management.     

Reproduction and development of <Emphasis Type="Italic">Pholis picta</Emphasis> (Perciformes: Pholidae) and <Emphasis Type="Italic">Opisthocentrus zonope</Emphasis> (Stichaeidae)

In the Peter the Great Bay (the Sea of Japan), reproduction and embryonic larval development of Pholis picta and Opisthocentrus zonope are investigated. Both species spawn in November–December at the water temperature decreasing from 7.0 to 0.2°C. Fecundity of Pholis picta is 494–1228 eggs, and of Opisthocentrus zonope—368–1360 eggs. Both species lay eggs in empty shells of Gray mussel. Parent fish permanently stay in the shell but do not actively care for the eggs. Morphological changes in the process of embryogenesis are compared between the related species. Prolarvae and larvae are described for identification, with special attention to pigmentation. The spawning behavior of adult fish and behavior of prolarvae are described.     

Evidence of spawning by green sturgeon, Acipenser medirostris, in the upper Sacramento River, California

This study reports the only direct evidence of spawning of green sturgeon, Acipenser medirostris, in the upper Sacramento River, CA. Two green sturgeon eggs were collected with substrate mats immediately below Red Bluff Diversion Dam. One green sturgeon larva was collected with a larval net at Bend Bridge. We concluded that green sturgeon spawn in the upper Sacramento River, both above and below RBDD. Temperature ranges in the study area (10–15°C) are similar to conditions used in successful artificial rearing of green sturgeon and do not appear to be a limiting factor to successful spawning of green sturgeon; however, suitable habitat upstream of RBDD is inaccessible when dam gates are lowered.     

Flyingfish Spawning (Parexocoetus brachypterus) in the Northeastern Gulf of Mexico

A spawning aggregation of Parexocoetus brachypterus was observed in the northeastern Gulf of Mexico over the outer continental shelf, 100km south of Mobile, Alabama. The event was considered to be a spawning aggregation given the remarkably high abundance of flyingfish observed, together with unusually vigorous flying, jumping, and swimming activity near the surface, and observations of both males and females exuding ripe sex products when landed. The spawn occurred during May 2001 just after moonrise 2 days post full moon. More than 1000000 flyingfish were estimated to have participated in the spawn. Male flyingfish were three times more abundant than females, consistent with observations of 3–4 flyingfish grouped together before and after the spawning aggregation, if several males were simultaneously pursuing a single female. Although egg attachment to flotsam is the only reproductive mode previously described for flyingfishes with demersal eggs, the P. brachypterus spawn occurred in the absence of flotsam. Other possible egg development modes include egg suspension upon current, mid-water suspension above pycnocline or upon topographically induced turbulence, or benthic.     

Predation of Northern Pike (Esox lucius L.) Eggs: A Possible Cause of Regionally Poor Recruitment in the Baltic Sea

Northern pike (Esox lucius) spawning habitat and egg mortality were studied in three spawning areas in 2001 along the Swedish coast of the Baltic proper: the Blekinge Archipelago, Kalmar Sound and coastal freshwater streams. Spawning peaked during the last week of April in streams, at temperatures ranging from 7.7 to 8.9 °C and during the first week of May in brackish waters, at temperatures ranging from 8.9 to 13.8 °C. Spawning occurred in shallow waters, at depths between 0.2–1.5 m, but generally most of the spawn was found in the shallowest areas. In streams, eggs were mainly attached to emersed vegetation, while in brackish sites pike eggs were well scattered among flooded emersed plants, submersed plants and filamentous algae. Mean egg density varied between 469–1829 m^–2 with the lowest density observed in Kalmar Sound. The calculated egg loss occurring from approximately one day after spawning to one day before hatching ranged from 41±7% in coastal streams to 67±6% in the Blekinge Archipelago and 100% in Kalmar Sound. The significant removal of eggs from spawning sites in Kalmar Sound and Blekinge was most likely due to predation from several fish species. In situ observations and stomach analyses suggested that many pike eggs in Kalmar Sound were lost to the three-spined stickleback (Gasterosteus aculeatus), a species that presently dominate the littoral small fish community. This study therefore suggests that egg predation by sticklebacks and other fishes may be a possible cause of the reported poor recruitment of coastal pike populations in the Kalmar Sound region.     

Aggregation and spawning by lampreys (genus Ichthyomyzon) beneath cover

Synopsis Lampreys are generally reported to spawn in shallow water on open, gravel bottoms. During surveys in Wisconsin and Minnesota, we regularly observed aggregations of adult Ichthyomyzon c.f. gagei, I. castaneus, and I. fossor beneath such cover objects as boulders, woody debris, and, at one site, vegetation. In some cases, observations of eggs or rapid quivering by individual lampreys indicated that spawning was occurring. The literature includes scattered anecdotal reports of similar behavior in other populations of Ichthyomyzon. Our data for I. c.f. gagei suggest that aggregations beneath cover objects occur at a greater range of depths than those in the open, but that aggregations in the open can contain greater numbers of individuals. Facultative spawning beneath cover objects may permit lampreys to spawn in deep waters with swift current where spawning could not otherwise occur. Moreover, this behavior may reduce the vulnerability of spawning lampreys to some types of predators.     

The spawning behaviour of the endangered freshwater fish Ladigesocypris ghigii (Gianferrari, 1927)

Ladigesocypris ghigii (Gianferrari, 1927), commonly called gizani, is an endangered freshwater fish endemic to the Greek island of Rhodes. The spawning behaviour of gizani was studied in aquaria, to develop an artificial breeding technique for this endangered species. Spawning in captivity was recorded over 41 spawning days between 15 February and 14 July 2001, under constant temperature (18 or 21°C) and photoperiod 14L/10D. The number of spawning acts in a day was 82 ± 28. No aggressiveness and no territoriality were developed. The mating system of the fish was polygamous, with females spawning more than once. In captivity, eggs are laid either on aquatic plants or on gravel, while in nature fish spawn mainly on algae and plants. The latter suggests that, as far as breeding substrate is concerned, gizani is an opportunistic species using different substrates when necessary.     

Influence of temperature during four following spawning seasons on the spawning effectiveness of common bream,Abramis brama (L.) under natural and controlled conditions

The common bream, Abramis brama (L.) in Kortowskie Lake (north-eastern Poland) usually spawn when the water temperature during the late spring rises to 20 °C. The optimal water temperature for embryonic development of this population is 21 °C. However, in some cases, the temperatures of the spawning grounds during bream spawning are much higher, becoming semi-lethal or even lethal for bream embryos. The aim of the study was to investigate the natural and artificial spawning effectiveness of bream during a 4-year study regarding the reproductive effectiveness of the wild bream population in relation to thermal fluctuation (optimal and semi-lethal) of their ecosystem during the natural spawning season. During four following seasons, the bream spawners, as well as the eggs, were collected from the spawning grounds and incubated at optimal (21 °C) and semi-lethal (23 °C) temperatures. The spawning of mature bream was artificially induced and the obtained eggs were also incubated at the same temperatures. The period of observed spawners on the spawning grounds was different in different years: the longest time of bream spawning was in the second year of the study and the shortest was during the third year of the study. In the last year, a decrease in water temperature caused a break in the spawning. Thermal changes in water temperature during the spawning season may have caused a high mortality level of bream embryos and decreased the recruitment of the next species generation.     

Seasonal and interannual variation of ichthyoplankton off Mauritania

Changes of the quantitative and qualitative composition of ichthyoplankton off Mauritania (21–16° N) in different seasons of 1997–2008 are analyzed. In this area, pelagic eggs and larvae of over 120 fish species belonging to 71 families are recorded. In warm periods, the fish of the tropical fauna intensively spawn off Mauritania; round sardinella Sardinella aurita, West-African horse mackerel Trachurus trecae, and jack mackerel Caranx rhonchus are dominant. In cold periods, active spawning of fish belonging to the tropical fauna is recorded, the most abundant are European pilchard Sardina pilchardus, European horse mackerel Trachurus trachurus, and Atlantic mackerel Scomber japonicus. The spawning biomass of principal commercial fish species is calculated on the basis of the quantity of eggs laid by females. Environmental factors control fluctuations of abundance and distribution of ichthyoplankton in the considered region.     

Phytoplankton as a stimulus for spawning in three marine invertebrates

A distinct annual reproductive cycle with spring spawning was observed in Strongylocentrotus droebachiensis Müller, Tonicella lineata Wood and Tonicella insignis Reeve. This study gives evidence that the cue for spawning in these species is the spring phytoplankton bloom. In 1973 spawning occurred abruptly in early April at the time of the spring phytoplankton outburst, but in 1974 spawning was less abrupt corresponding to the slow development of the phytoplankton bloom in that year. Animals were collected prior to spawning and maintained in the laboratory under various temperature and light regimes: at 5 ° and 14 °C in darkness, and at 5 ° and 14 °C in light conditions similar to those in the field. These animals did not spawn when spawning occurred in the field, but animals returned to the field from the laboratory did spawn. In the laboratory a large proportion of animals spawned when they were exposed to phytoplankton collected with a 50μm mesh net. The results suggest that some substance bound to or released by phytoplankton stimulates spawning. For species with planktotrophic larvae the synchronization of spawning with the phytoplankton bloom increases the probability of favourable food and temperature conditions for the development of the larvae and juveniles.     

Reproductive biology of female bigeye tuna Thunnus obesus in the western Pacific Ocean

The reproductive biology of female bigeye tuna Thunnus obesus was assessed by examining 888 fish (ranging from 84·9 to 174·4 cm fork length, L_F) caught by Taiwanese offshore longliners in the western Pacific Ocean from November 1997 to November 1998 and November to December 1999 and 258 gonad samples from these fish. The overall sex ratio of the catch during the sampling differed significantly from 0·5, but males were predominant in sizes >140 cm L_F. Reproductive activity (assessed by histology), a gonado‐somatic index, and the size‐frequency distributions of whole oocytes indicated that spawning occurred throughout the year and the major spawning season appeared to be from February to September. The estimated sizes at 50% maturity (L_F50) of females was 102·85 cm (95% c.i .: 90·79–110·21 cm) and the smallest mature female was 99·7 cm L_F. They are multiple spawners and oocytes develop asynchronously. The proportion of mature (0·63) and reproductively active (0·70) females with ovaries containing postovulatory follicles indicated that they spawn almost daily. Batch fecundity for 15 females with the most advanced oocytes (>730 µm) ranged from 0·84 to 8·56 million eggs (mean ± s.d . = 3·06 ± 2·09). The relationships between batch fecundity (F_B, in millions of eggs) and L_F (cm) and round mass (M_R, kg) were (r² = 0·84) and (r² = 0·80), respectively. The parameters estimated in this study are key information for stock assessments of T. obesus in the western Pacific Ocean and will contribute to the conservation and sustainable yield of this species.     

Communal Spawning in the Common Frog Rana temporaria– Egg Temperature and Predation Consequences

Females of the common frog, Rana temporaria, spawn synchronously at communal breeding sites, forming a communal egg mass of individual spawn clumps. A total of four spawning sites were studied. In the centre of the communal egg mass, daily maximum temperature was higher and minimum temperature lower than further out. Spawn clumps in the centre of the communal egg mass developed faster than single spawn clumps. In the centre of the egg masses, some spawn clumps suffered almost total egg mortality. This was probably the consequence of a cold spell with sub‐zero temperatures in combination with a tendency for low minimum temperatures in the centre. In a laboratory study, worm leeches, Erpobdella spp., fed readily on eggs of common frog, while horse leeches, Haemopis sanguisuga, hardly ate any eggs. At the spawning sites, most worm leeches were found in single spawn clumps, far from the communal egg mass. Females which spawned late, when most of the spawning was over, preferred to spawn in the centre of the communal egg mass. This suggests that there is a net advantage for eggs in spawn clumps laid in the centre.     

Reproduction of the introduced oyster Crassostrea gigas (Bivalvia: Ostreidae) cultured on rafts in Spain

The oyster Crassostrea gigas was introduced in Spain for aquaculture purposes; however, until now, it is not known whether populations are established in the wild, being necessary to define whether this species is spawning and which environmental variables trigger this process. The influence of environmental parameters on the reproduction of C. gigas was evaluated from January 2008 to October 2009 with oysters grown on a raft in the Ría de Arousa (Galicia, NW Spain). Temperature and chlorophyll a are directly correlated to sexual maturation. Oysters can mature at temperatures below 14°C. The temperature necessary for spawning differs between the sexes, requiring a temperature above 15°C for males and 18°C for females. Females had a single massive spawn between June and September, while males had partial spawning from May to December with two peaks, one in May–September and another in October–December, with the second peak more pronounced. The first spawning peak is related to high temperatures and concentrations of chlorophyll a, and the second spawning peak is mainly related to the food availability in the water. The spawning asynchrony may be impeding establishment of wild C. gigas populations in Spain.     

Reproductive strategy,spawning induction,spawning temperatures and early life history of captive sicklefin chub Macrhybopsis meeki

Macrhybopsis reproduction and propagule traits were studied in the laboratory using two temperature regimes and three hormone treatments to determine which methods produced the most spawns. Only sicklefin chub Macrhybopsis meeki spawned successfully although sturgeon chub Macrhybopsis gelida released unfertilized eggs. All temperature and hormone treatments produced M. meeki spawns, but two treatments had similar success rates at 44 and 43%, consisting of a constant daily temperature with no hormone added, or daily temperature fluctuations with hormone added to the water. Spawns consisted of multiple successful demersal circular swimming spawning embraces interspersed with circular swims without embraces. The most spawns observed for one female was four and on average, 327 eggs were collected after each spawn. The water‐hardened eggs were semi‐buoyant and non‐adhesive, the first confirmation of this type of reproductive guild in the Missouri River Macrhybopsis sp. From spawn, larvae swam vertically until 123 accumulated degree days (° D) and 167° D for consumption of first food. Using average water speed and laboratory development time, the predicted drift distance for eggs and larvae could be 468–592 km in the lower Missouri River. Results from this study determined the reproductive biology and early life history of Macrhybopsis spp. and provided insight into their population dynamics in the Missouri River.     

Captive hybridization of two geographically isolated pygmy angelfish species,Centropyge fisheri and Centropyge resplendens

This study documents the rearing of two pygmy angelfish species, Centropyge fisheri and Centropyge resplendens, and the early life history and reproduction of their hybrid offspring. A C. fisheri female, collected from Hawaii, and a C. resplendens male, captive‐bred from parental stock collected from Ascension Island, were maintained at the hatchery facility for 7 months. Continuous spawning was achieved at a photoperiod cycle of 14L:10D and a water temperature of 26·5° C, range ±1° C. Over the 110 day period, the C. fisheri female spawned 102 times, 57% of which resulted in embryos (fertilized eggs). The mean ±s.d. fecundity per spawn was 730 ± 459 eggs (range 52–1967). Fertility (% eggs that developed into embryos) of all eggs that were preserved was 22·4 ± 25·6%. A total of 235 hybrid juveniles were raised through metamorphosis with an average larval survival of 16·4%. Eight F₁ hybrid juveniles isolated for further study began to display signs of reproductive behaviour c. 300 days post‐hatch (dph). Spawn resulting in non‐fertile eggs were first obtained 319 dph, and fertilized eggs developing into embryos were obtained after 411 dph from at least two female individuals. While no attempt was made at rearing the F₂ larvae, embryo and larval development were normal up to 8 dph. Reproduction and development observed for all hybrid generations in this study were normal, similar to other Centropyge species and indicates a very close phylogenetic relationship between what are currently considered distinct species, e.g. C. fisheri and C. resplendens.     

Aggregation and spawning of the humphead wrasse Cheilinus undulatus (Pisces: Labridae): general aspects of spawning behaviour

The humphead wrasse Cheilinus undulatus formed resident spawning aggregations daily after high tide at specific locations along the seaward edge of the Palau barrier reef. The location and extent of one aggregation site remained consistent for 6 years with no physical features distinguishing it from adjacent areas. Spawning was documented most months and probably occurred year round with possible seasonal and lunar variation. Spawning males arrived first at the site, followed by females and potentially small primary males. The aggregation female to male sex ratio was estimated to be between 6:1 and 10:1. A maximum of 15 males and 100–150 females were observed at the site. A male courtship posture with the anal fin pointed, the caudal fin folded down and the dorsal fin folded against the body was maintained while swimming a few metres off the bottom in view of females. When ready to spawn females rose up as the posturing male passed and the pair released gametes in a relatively sedate fashion near the surface along the shelf break. No attempted predation on spawning adults was seen. Egg predation after spawning was uncommon. On days with early to mid‐day high tides the spawning period started 2·0–2·5 h after high tide when the speed of lagoon–ocean tidal currents peaked and lasted c. 1 h. On days with later afternoon high tides, spawning occurred sooner after high tide and before current speeds peaked. Other fishes with planktonic eggs spawned at the site as pairs or small groups in a rough succession after high tide with C. undulatus, the last species to spawn.     

Temperature influence on the spawning performance of artificially-matured Japanese eel, Anguilla japonica, in captivity

We studied the influence of temperature on the spawning performance of artificially matured Japanese eels, Anguilla japonica, in captivity. We used routine hormone injections to bring females and males to maturity in separate aquaria. We recorded the behavior of three pairs of such hormone-treated matured eels in an aquarium (2 replicates) at four temperatures: 14, 18, 22, and 27°C, respectively. They became active and frequently left the bottom swimming in the water column, and spawning events occurred. Females released eggs in the water column around the activity peaks. Males preceded females in reaching activity peaks (presumably the timing of sperm ejection and egg release), possibly resulting in the low fertilization we observed in this experiment. Males and females returned back to the aquarium bottoms and became quiet after spawning. On several occasions, male-female or female-female pairs were observed to ‘cruise together’ in the water column for several to tens of seconds prior to egg releasing, but no courtship behavior indicative of spawning such as pairing and chasing was observed in the eels in our study. Our results suggest that 18–22°C might be the thermal preference for spawning for Japanese eels, which approximates the temperature range of the 500 m deep water layer around the Mariana Islands seamount area, the presumed spawning site for the Japanese eel.

Aspects of the spawning of western Atlantic butterflyfishes (Pisces: Chaetodontidae)

Synopsis The status of knowledge of spawning among the five shallow waterChaetodon species in the western Atlantic is reviewed. Spawning has been observed for three species in Puerto Rico, St. Croix and the Bahamas, with possible courtship in a fourth.Chaetodon aculeatus spawned near the time of sunset over objects on the reef as single female/male pairs or as two females and one male, with pair spawning in rapid succession. Spawning occurred during much of the lunar month from February to April and it is uncertain whether any lunar periodicity to spawning exists. Male-male aggression was noted. Spawning sites (coral heads) were alternated daily and it is likely that females spawn only once every two days. A single female produced as many as 2090 eggs in a single spawning.Chaetodon capistratus spawned during much of the lunar month from February to April. It spawned about 5 min afterC. aculeatus, occasionally using the same sites, and alternated sites daily. A female produced as many as 3710 eggs in one spawning.Chaetodon striatus spawned from February to April but it is unknown if it has any lunar spawning cycle. No predation attempts by piscivores on spawning adults were seen. Predation byMelichthys niger on eggs ofC. striatus occurred. No egg predation was observed forC. aculeatus andC. capistratus. With an assumed four month reproductive season, alternate day spawning and observed egg production values,C. aculeatus andC. capistratus produce respectively about 100 000 and 200 000 eggs per large female per year. The reproductive strategy of smaller species may be to produce moderate numbers of eggs per day over a spawning season of at least a few months while larger species may produce more eggs per day for a shorter period.     

Spawning Periodicity, Spawning Migration, and Size at Maturity of Green Sturgeon, Acipenser medirostris, in the Rogue River, Oregon

The Rogue River, Oregon represents one of three important spawning systems for green sturgeon, Acipenser medirostris, in North America. In this paper we describe the spawning migration, spawning periodicity, and size at maturity for green sturgeon caught in the Rogue River during 2000–2004. Green sturgeon were caught by gill net or angling; 103 individuals were tagged with radio or sonic transmitters (externally or internally). Green sturgeon caught by gill net and angling ranged from 145 cm to 225 cm total length. Histological and visual examinations of gonad tissues indicated that most green sturgeon were spawning or post-spawning adults that entered the Rogue River to spawn. Ripe individuals were caught when water temperature was 10–18°C. Specimens carrying transmitters migrated 17–105 km up river; reaches consisting of likely spawning sites were identified based on sturgeon migratory behavior. Most green sturgeon remained in the Rogue River until late fall or early winter when flows increased, after which they returned to the ocean. Eight green sturgeon (males and females) returned to the Rogue River 2–4 years after leaving, entering the river during March, April, and May when water temperatures ranged from 9°C to 16°C. None of the 103-tagged individuals entered the Rogue River during successive years. There appear to be few known natural threats to adult green sturgeon in the Rogue River. However, our data suggest that a high percentage of adults that spawn in the Rogue River (particularly males) were susceptible to harvest by commercial, Tribal, and sport fisheries after leaving the system because they were not adequately protected by maximum size limits during the period of this study. The implications of maximum size limits (or lack of size limits) to green sturgeon are discussed, and recent actions taken by Oregon and Washington Fish and Wildlife Commissions to manage green sturgeon more conservatively are presented.     

Predation on eggs by conspecific males in two Japanese damselfishes,Pomacentrus nagasakiensis andChromis notatus notatus,after removal of egg-guarding males

Egg predation by conspecific males of damselfishes,Pomacentrus nagasakiensis andChromis notatus notatus, was studied at Bohnotsu (31°15′ N, 131°15′ E) and Tsuyazaki (33°47′ N, 130°29′ E), respectively. InP. nagasakiensis, 7 egg-guarding males were removed from nests, and intrusion and egg predation by conspecific males took place in all of the nests within an average time of 12.2 min. Frequency of attacks on eggs by other reef fishes during the period between the removal of egg-guarding males and intrusion of conspecific males was lower than expected, considering the frequency of aggressive displays of the egg-guarding males. The results of male removal experiments forChromis notatus notatus were almost the same, with intrusion and egg predation by conspecific males occurring in all 12 of the nests from which egg-guarding males had been removed. SixP. nagasakiensis and 15C. notatus notatus which intruded into the nests and preyed on eggs were collected. All were males except for 1C. notatus notatus female. Results suggest that these males which intruded into vacant nests to eat eggs did not have clutches of their own during the spawning bouts when the experiments were done. Results also showed that the intruding males were not inferior to egg-guarding males in standard length, gonadosomatic index, and condition factor. It is clear that males which do not have their own clutches during at least 1 spawning bout and prey on others' eggs when egg-guarding males disappear are common in these 2 gregariously nesting damselfishes. It is discussed that conspecific eggs are potentially a good food source not only for other species of reef fishes but also for conspecific males which do not have their own eggs during the spawning bouts. The origin of males wich prey on eggs of other conspecifics is also considered. Some aspects of egg-guarding and aggressive behavior of males in damselfishes are discussed.