Spawning characteristics of the anadromous brown trout in a small Swedish stream

The spawning pattern of the anadromous brown trout Salmo trutta was studied in Själsöån, a small stream in Gotland, Sweden, during eight winters between 1992–1993 and 1999–2000. The total length ( L _T) at spawning was normally distributed (185–890 mm) for females and multimodal for males (300, 400 and 550 mm most frequent length classes). Spawning males were significantly younger (2+ to 4+ years) than females (3+ to 5+ years). The sex‐ratio at the beginning and at the end of the spawning season favoured males. The mean ±  s . d . number of spawners was 70 ± 16 individuals per year. Migration into and out of the stream occurred between November and June. The highest number of spawning fish was found in the stream at the end of November or at the beginning of December. Migration mainly occurred during high water flow and at night. The majority of the females entered the stream and spawned the same (29·3% of all the females) or the next night (32·8% of all the females) while males may have stayed for 2 to 3 weeks (21·3% of all the males) in the stream before spawning. Males usually remained much longer in the stream (mean ±  s . d . 45 ± 56 days) than females (16 ± 30 days). Females lost more mass in the stream (mean ±  s . d . 17·3 ± 8·6%) than males (7·7 ± 9·6%). For both sexes, mass loss was positively correlated with the time spent in the stream. Only 7·3% of the males and 5·7% of the females occurred in the stream for >1 year. Spawning took place only during the night.     

Biology of the amphioxus,Branchiostoma belcheri in the Ariake Sea,Japan II. Reproduction

We investigated the reproduction of the amphioxus Branchiostoma belcheri in the southern Ariake Sea, Japan, from 1999 to 2002. Gonads were very small or almost absent from September to December and began to develop in January. Changes in the gonad length index indicated that spawning began in mid June, after the gonads had attained maximum size. Although most gametes were extruded during the first spawning, some remained in the gonads. Shrunken gonads were much smaller but contained gametes, and the second spawning occurred around 10 July. It was unclear whether all adults spawned twice, but a large proportion of individuals did. After the first spawning, both males and females lost 30% of their body weight. Most one-year-old individuals did not spawn, and the minimum size at maturity was ca. 20 mm. We found no termination of reproduction among very large individuals. The average number of gonads was significantly larger on the right side of the body (26.2 in males and 26.1 in females) than on the left side (24.0 in males and 23.5 in females). We found two hermaphrodites in a total of 11,184 specimens examined. Each had four or three ovaries among a total of 45 or 54 gonads.     

Reproductive biology of the rosylip sculpin, an intertidal spawner

Rosylip sculpin Ascelichthys rhodorus spawned in the intertidal during the winter in the north‐eastern Pacific. Large numbers of males typically congregated at spawning sites, where females deposited clutches. The mating system of this species was external fertilization and group spawning at specific oviposition sites under boulders in the intertidal, and no alternative male mating strategies. Males were abundant at sites while oviposition was occurring, and most abandoned the sites as spawning tapered off seasonally despite the presence of developing clutches. Experimental removal of males from sites suggested that males provided some short‐term benefits to clutches, with catastrophic loss of clutches significantly lower when males were present. The large number of males at an oviposition site and histological evidence indicating high sperm production and storage of sperm prior to release suggest a high level of sperm competition in this species. This spawning pattern appears to differ in substantial ways from any other reported fish mating system.     

Synchronous female spawning and male mating behavior in a land-locked population of Japanese charr, Salvelinus leucomaenis japonicus

In resource-based promiscuous mating systems, synchronous spawning of females affects competition among males and variation in the reproductive success of males. We documented the mating behavior of Japanese charr (Salvelinus leucomaenis japonicus) through an annual breeding season to examine the relationship between female spawning synchrony and male mating behavior. Females spawned highly synchronously in the population studied, i.e., approximately half the spawning was finished within the first three days of the entire spawning season (11 days). The daily operational sex ratio (OSR) was nearly 1:1 through the spawning period. The number of males around a spawning female was very small (1.21+/-0.49 males per female) over the spawning ground and period, suggesting that a competitive male could effectively chase subordinate males away from a spawning female. A few males attempted to sneak near the oviposition site of females (16%; 9 of 57 breeding groups), while some males adopted sneaking tactics in the initial phase of females' spawning (24%). We did not observe any males to succeed in sneak fertilizations. We conclude that in this Japanese charr population, the synchronous spawning of females was related to the unbiased daily OSR, male aggregation around females, and consequently whether and how efficiently males engaged in sneak mating behavior.     

Breeding biology of a non-diadromous galaxiid, Galaxias vulgaris Stokell, in a New Zealand river

In the Glentui River, Canterbury, New Zealand, Galaxias vulgaris Stokell spawned in late winter and early spring (from July to September), the onset of spawning being temperature-dependent. No females matured in their first year, but 95 and 68 % of age 0+ males were mature in consecutive years. With the exception of one female, all fish aged 1 + and older spawned. In mature fish, overies reached nearly 23%, and testes 11%, of somatic weight. Maturity in males depended on size, whereas in females, age appeared to be the major factor affecting maturity. Recruitment eggs for next season's spawning were distinct from primary oocytes soon after the ripe eggs were shed. Egg numbers varied between 284 and 1911 per fish, and weight was the best indicator of fecundity. Sex ratios of whole samples were not significantly different from 1 : 1, but ratios of potential spawners revealed an excess of males, due mainly to the presence of age 0 + fish. Age0+ males probably play an important role in adverse conditions and act as a form of insurance by significantly increasing the proportion of ripe males, thereby ensuring that all eggs are fertilized. The nest, egg mass and behaviour during the spawning period are described. More than one female may lay eggs in each nest and it is probable that each egg mass receives sperm from more than one male. It is suggested that the presence of fewer and larger eggs in G. vulgaris , compared with the diadromous galaxiids, is the result of a more precise fertilization process.     

Reproductive cycle and reproductive output of the sea urchin Loxechinus albus (Echinodermata: Echinoidea) from Beagle Channel, Tierra del Fuego, Argentina

Reproductive cycle, frequency and duration of spawning, energetic content of gonads, and reproductive output of the common green sea urchin Loxechinus albus were analyzed in the Beagle Channel (Tierra del Fuego) between May 2004 and May 2005. Gonad indices (GI, percentages of gonad mass in total body mass) were significantly higher in March, April, July, and August than in November and May, thus showing a negative correlation with the photoperiod. Highest GI values of mature individuals were observed in August, and spawning occurred from September to December. In females, the mass-specific energy content of gonads (ECG) was highest in spawned gonads and lowest in mature ones, while in males ECG values were higher in immature stage and lower in premature and mature stages. High ECG values can be explained by the abundance of nutritive phagocytes. Both ECG and total gonad energy content (TECG) were higher in females than in males. Mean reproductive output was 7.28% for females and 6.15% for males (expressed as the difference between mean GI of mature and spawned gonads) and 25.02 kJ for females and 19.26 kJ for males (expressed as the difference between mean TECG of mature and spawned gonads).     

Reproductive biology of the endangered Oxleyan pygmy perch Nannoperca oxleyana Whitley

The reproductive biology of the Oxleyan pygmy perch Nannoperca oxleyana is described from simultaneous studies of wild populations in north-eastern New South Wales and mature fish held in aquaria. In the wild, 50% of males and females matured at total lengths of 24·0–25·9 and 28·0–29·9 mm, respectively. The species displays sexual dichromatism during the spawning season, with males developing more intense red and brown fin and body colouration, and black pelvic fins. Captive male broodfish displayed territoriality during the breeding season, closely guarding sites within artificial, plant-like substrata in which pairs of fish spawned adhesive eggs. Protracted serial spawning of wild and captive fish occurred from September to April and May at mean water temperatures ≥16·6° C and day length ≥10·7 h. Captive broodfish spawned on an average of 57% of days during the 256 day spawning period. Gonado-somatic indices averaged 0·7% for all ripe males and 4·1–4·2% for all ripe females collected. Mean total and batch fecundities of captive females were 1323 eggs per fish and 7·8 eggs per fish per day, respectively, and relative fecundity was 587 eggs g⁻¹ of body mass. Batch fecundity of wild females was estimated at 7·8 eggs per fish. The adaptive significance of this reproductive strategy in a harsh, variable environment is discussed.     

Aspects of the reproductive biology of the South African polychaete,Arenicola loveni loveni (Kinberg 1866)

Summary

The annual cycles of gametogenesis, spawning and fertilization biology were investigated in the South African polychaete Arenicola loveni loveni (Kinberg, 1866). Sexes are strictly separate (gonochoric) with a 1:1 ratio and gametogenesis takes place in the coelomic cavity. Reproduction is iteroparous and occurs during a synchronized annual epidemic spawning event during the summer months of February or March, which lasts no longer than 2 weeks at around the time of highest annual seawater temperatures. A slight inter-annual variation in spawning time was observed between 2003 and 2004. Annual fecundity was estimated as 311,200 (± 82,040 standard deviations) oocytes per female per year. Oocytes are arrested at prophase I of the first meiotic division and require a maturation step prior to spawning and subsequent fertilization. Mean spawned oocyte diameter was 141.16 μm ± 0.43 SE. Sperm develop as morulae in the coelomic cavity and also require a maturation step prior to spawning. Spawning can be achieved by injection of prostomial homogenate in both males and females and by injection with 8,11,14- e cosatrienoic acid for males and can be delayed by temperature manipulation. Oocyte maturation and sperm maturation can be induced in vitro by incubating in prostomial homogenate.     

Reproductive Biology of the Coral-reef Goby, Asterropteryx Semipunctata, in Kaneohe Bay, Hawaii

A population of the Hawaiian coral-reef goby, Asterropteryx semipunctata, was sampled over a 12-month period to determine basic demographics and reproductive parameters. The sexes did not differ in median length or weight, although the largest males were considerably longer and heavier than the largest females. Overall adult sex ratio was 1:1; monthly sex ratios did not differ from unity except in June, when there was a significant female bias. Minimum age at maturity (17.5–19mm SL) was estimated to be 4.5–5 months after hatching. Nearly all fish over 22mm SL were mature. Mature females were found in all months of the year, and females that showed evidence of recent or imminent spawning were collected in every month except December. Gonadal analyses indicated a peak in breeding during the summer (May–July) and minimal spawning during the winter (January–February). Between 20% and 30% of females showed evidence of having spawned within the 24-h period prior to collection; therefore, it was estimated that females spawned, on average, at least once every five days and perhaps as frequently as every three days. Mean batch fecundity was 708 eggs (± 418), and was not well predicted by standard length, body weight, or somatic condition. Relative batch fecundity (mean = 1.44 oocytes mg^–1 somatic wet weight) varied seasonally, with higher values in spring and summer (April–July) than in fall and winter (September–January). Reproductive parameters are compared and contrasted with those of other gobiid fishes to elucidate general differences between temperate and tropical species.     

Annual reproductive cycle and sexual dimorphism in the dragonet,repomucenus valenciennei, in tokyo bay, japan

The annual reproductive cycle of the dragonet,Repomucenus valenciennei, from Tokyo Bay, Japan, was studied by analysis of seasonal trends in gonadosomatic indices and histological observations of gonads. Sexual dimorphism in the growth of several body parts relative to standard length (SL) and changes in color pattern of the first dorsal fin with growth were also investigated. The spawning season lasted from spring (April [1991] or February [1992]) to autumn (October) with two spawning peaks, in spring and autumn. In spring, only one-year-old (age 1+) fish spawned, age 0+ females not spawning until autumn, at which time they had reached age 1+. Likewise, histological observations of males indicated that testes had reached full maturity by 80 mm SL (age 1+). The minimum mature size of females was estimated as 60 mm SL. In males 45–80 mm SL, the first spine of the first dorsal fin, last ray of the second dorsal fin, last ray of the anal fin, and caudal fin ray showed strongly positive allometry, indicating rapid growth of these structures relative to SL. Subsequently, their growth returned to an isometric pattern in males>80 mm SL. In females, on the other hand, the same body parts showed slightly positive allometry throughout their growth. The color pattern on the first dorsal fin also changed in males 45–80 mm SL.     

Feeding behaviour of cod (Gadus morhua) in relation to spawning

The food consumption and egg production of 26 adult (13 female and 13 male) Atlantic cod ( Gadus morhua ) were monitored during prespawning, spawning and postspawning periods. Females spawned from late January to mid-April. Feeding activity occurred from December to early January and ceased for females, on average, 36 days (15–54 days) before the onset of spawning. The duration of spawning by females was, on average, 42 days (10–61 days) and feeding was suppressed by both sexes during the first three-quarters of each female's spawning period. Mature females went, on average, 70 days or 19% of the year without eating. An abrupt increase in feeding activity, particularly by females, occurred during the last quarter of spawning or shortly after the release of the last egg batch (on average, feeding started again after 91% of a female's eggs had been released or 82% of egg batches). Females consumed greater quantities of food than males during both winter and postspawning feeding periods. During spawning, females lost, on average, 29% of their body weight and males 14%. Fecundity ranged from 0.75 to 3.97 million eggs per female. The volume of eggs produced by four individual females (range = 1285–5995 ml in four to 11 batches) ranged from 99 to 195% (mean 150%) of a female's postspawning body volume. Six immature cod fed throughout the experimental period and gained, on average, 8% of initial body weight. Laboratory results were supported by stomach fullness index values of Georges Bank cod exhibiting different maturity states.     

Reproductive biology of brown trout, Salmo trutta macrostigma Dumeril 1858, in a tributary of the Ceyhan River which flows into the eastern Mediterranean Sea

The study describes some key elements of the reproductive biology, including spawning season, age at sexual maturity, fecundity and egg diameter of the native brown trout, Salmo trutta macrostigma, in a tributary of the Ceyhan River. A total of 197 brown trout (118 females and 79 males) were captured in 2000–2001 by electric fishing. In observations on monthly changes, the gonadosomatic index (GSI) and the monthly frequency distribution of egg diameter confirmed that spawning lasted from November to January. Some 27.7% of the females and 62.5% of the males attained sexual maturity in their second year. The smallest fork length (FL) of brown trout attaining sexual maturity was 17.4 cm for males and 17.8 cm for females. Mean fecundity in age groups II, III, IV and V were 360, 452, 693 and 1283 eggs per female, respectively. One 9‐year‐old female had a unique 3232 egg count. The mean fecundity of the sampled population was 554 eggs per fish, positively correlated with the FL (mm) (R = 0.8227 ) and body weight (R = 0.8130). The diameter of mature eggs in the spawning season ranged from 3.250 to 5.930 mm, with a 4.146 mm average. Mean egg diameter in age groups II, III, IV and V in the spawning season were 0.813, 3.799, 4.663 and 5.243 mm, respectively. Fecundity, egg weight and diameter were statistically different in all age groups.     

Genetic mating patterns studied in pools with manipulated nest site availability in two populations of Pomatoschistus minutus

Pomatoschistus minutus show paternal care in a resource defence mating system. We investigated the effect of nest-site availability on parasitic spawning. Each experimental pool contained four potentially nest-building males, four females and nests-sites in shortage (2) or excess (6). Both treatments were conducted in two populations; one with natural nest-sites in excess, one with a nest-site shortage. Microsatellite-DNA revealed that all nest-holders had fertilized most of the eggs they tended. Yet, 35% of the nests contained eggs fertilized by another male and 14.4% of the males had performed parasitic spawning. There was no site or treatment effect. Several females spawned in two nests, which coincided with parasitic spawnings, suggesting a cost to the nest-holder in terms of lost mating success. Nest-holders with and without eggs and non-nesting males all spawned parasitically, generating a significantly lower opportunity for sexual selection compared to if there had been no parasitic spawning.     

Spawning ecology of flannelmouth sucker, Catostomus lattipinnis (Catostomidae), in two small tributaries of the lower Colorado River

We report the first published accounts of spawning behavior and spawning site selection of the flannelmouth sucker in two small tributaries of the lower Colorado River in the Grand Canyon, Arizona. Spawning was observed on 20 March 1992 and from 28 March to 10 April 1993 in the Paria River, and from 16 to 19 March 1993 in Bright Angel Creek. Flannelmouth suckers exhibited promiscuous spawning behavior–individual females were typically paired with two or more males for a given event and sometimes changed partners between events. Multiple egg deposits by different females sometimes occurred at one spawning site. Flannelmouth sucker selected substrates from 16 to 32 mm diameter in both streams. Spawning occurred at depths of 10 to 25 cm in the Paria River and 19 to 41 cm in Bright Angel Creek. Mean column water velocities at spawning locations ranged from 0.15 to 1.0 m sec^-1 in the Paria River and from 0.23 to 0.89 m sec^-1 in Bright Angel Creek. Water temperatures recorded during spawning ranged from 9 to 18° C in the Paria River and 13 to 15° C in Bright Angel Creek. Spawning flannelmouth sucker ascended 9.8 km upstream in the Paria River and 1.25 km in Bright Angel Creek. Spawning females (410–580 mm) were significantly larger than spawning males (385–530 mm) in the Paria River. The mean size of spawning fish in the Paria River was significantly smaller than the entire stock, averaged throughout the study period (380–620 mm). However, fish spawning in 1992–1993 averaged 53 mm larger than fish spawning in the same reach of the Paria River in 1981, indicating a shift in the size structure of this stock.     

Biology of the radiated shanny Ulvaria subbifurcata Storer in Newfoundland (Pisces: Stichaeidae)

Ulvaria subbifurcata is found on the north-east Atlantic coast of North America. Fish less than 55 mm preyed predominantly on copepods, while larger ones ate mainly nereids; polynoids and amphipods were eaten by all sizes. These four food items comprised the main food of the radiated shanny. Spawning occurred in May with the fish first spawning at age three to five. No conspicuous secondary sexual characters were observed. Females spawned once per year, producing a demersal egg mass. Males spawned up to four times and tended the egg mass (or masses). Incubation lasted 35–40 days, and the pelagic larvae settles on the bottom by August. Adult males tended to be larger than females of the same age but little difference was found sexually in the length–weight relationships. Ulvaria subbifurcata larger than 60 mm are nocturnal. This may reduce predation by, and competition with, other inshore benthic fishes.     

Reproductive biology of racer goby Neogobius gymnotrachelus in the Włocławski Reservoir (Vistula River, Poland)

Initial studies on the reproductive parameters and spawning behaviour of racer goby Neogobius gymnotrachelus, one of three Ponto‐Caspian gobiid species recently invading Polish waters, were carried out in W?oc?awski Reservoir (lower River Vistula, Poland), where spawning lasted from April to August. Males were on average about 23.3% longer and 53.8% heavier than females. The smallest female with mature gonads was 58 mm TL (estimated age 2+ years), and males were sexually mature at 59 mm TL (age of 1+ years). Gonado‐somatic index at the beginning of spawning was seven times larger in females (mean = 8.4) than that in males (mean = 1.2). Mean absolute fecundity was 952 eggs per female (361–2236). Egg diameter ranged from 0.140 to 1.558 mm, being of bi‐modal distribution, which suggests two or three spawning bouts. Length–frequency analysis of juveniles revealed a multimodal distribution. Specialized reproductive behaviour (nest construction and parental care of eggs) and an extended spawning period increase the probability that racer goby can successfully establish self‐sustaining populations in novel environments.     

Mating patterns of female Leon Springs pupfish Cyprinodon bovinus

In a field study of Leon Springs pupfish Cyprinodon bovinus, two questions about female promiscuity were investigated. First, were females selective in the males with whom they spawned or were they unselective, spawning randomly among males? Second, how promiscuous were the females, i.e. with how many males did they spawn? If simply spawning with many males maximized a female's reproductive success, then females might be expected to spawn randomly with as many males as possible. Alternatively, if females were selective but engaged in multiple mating, they would limit their spawning to preferred males. In the only wild population of this endangered fish, breeding males defend closely associated territories in the shallow margins of a single desert pool. No territories were observed elsewhere in the pool. Therefore, all territorial males were present simultaneously and females could survey all of them, depositing any number of eggs with one, a few or many males. Rather than spawning randomly, females surveyed many males first, visited relatively few males and ultimately spawned with a small fraction of those available males. With increasing numbers of spawns, however, females increased the number of different mates with whom they spawned. Thus, females showed a bet‐hedging tactic of having a narrow mate preference while also laying eggs in the territories of other males, possibly to reduce egg predation and to avoid inbreeding.     

Reproductive allocation in Aidablennius sphynx (Teleostei, Blenniidae): females lay more eggs faster when paired with larger males

Individuals are expected to invest more in current reproductive effort when paired with a partner of higher than average quality. Aidablennius sphynx is an external fertilizing fish with paternal care in which females gain direct benefits from spawning with large males, but often 'make do' with small males. In this study, female reproductive responses to large and small males were investigated. When paired with large males, females spawned more eggs per unit time (i.e., at a faster rate). There was no difference in the size of the eggs spawned by females in relation to partner size. By ovipositing at a faster rate, females may have allocated more reproductive effort to large males. In addition, since small males are known to release far fewer sperm than large males, females may have reduced their spawn rate with small males as a tactic to ensure fertilization.     

Some aspects of the reproductive biology of perch Perca fluviatilis L. Fecundity, maturation and spawning behaviour

Fecundity of perch estimated from a regression of egg. number on fish length varied from 6711 for a fish of 14.5 cm to 77978 for a female of 34. 5 cm. Other independent variables related to egg number were age, gonad weight and somatic weight. Mean egg diameter varied from 0.94 to 1.62 mm. Males matured in their second year at a length of 6 cm and above while all females spawned at age four at a length of 15–18 cm. A proportion of females at Davan spawned one year earlier than at Kinord and were also slightly smaller on spawning. Faster growth of Davan fish may have encouraged earlier maturation. Spawning behaviour is described from film material.     

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

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