Inter-annual variation in the gonad cycle of the mackerel icefish

Spawning by Antarctic fish is generally considered to be seasonal and restricted to a brief period during the autumn and winter. Arising from this it has been assumed that the gonadal maturation cycle is also closely associated with the time of year. The gonad maturation cycle of the mackerel icefish Champsocephalus gunnari was investigated using data collected during research surveys and from sampling the commercial fishery. Spawning appears to occur at the same time each year, but the timing of gonadal development is subject to a considerable inter-annual variation. The implications of this variation are discussed with respect to feeding conditions.     

太湖乔氏短吻银鱼的生物学

太湖产乔氏短吻银鱼于3月中旬至5月末产卵。卵具粘性。集中在有沉水植物着生的湖湾内产卵。生殖周期短,一年可达性成熟。繁殖力强。在水温14.5—25.0℃时,仔鱼在受精后118小时23分孵出。终生以浮游动物为食。生长较缓慢,接近一年才达上市规格。其寿命只一年,产卵后不久死亡。保护其产卵基质——沉水植物,以及适当地扩大银鱼网的网目,是关键的增殖措施。       

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.     

Reproductive biology of ningu, <Emphasis Type="Italic">Labeo victorianus</Emphasis> (Pisces : Cyprinidae), in the Kagera and Sio Rivers,Uganda

Synopsis We investigated aspects of the reproductive biology of the cyprinid fish, Labeo victorianus, locally known as ningu, in the Kagera and Sio Rivers, Uganda. These rivers represent the last remaining refuges for this species within Uganda. L. victorianus is a highly fecund, potamodrometic fish that migrates upstream to spawn. Spawning is generally synchronised with the bimodal water level maxima observed within the rivers. There were, however, some deviations from this pattern. We caught sexually mature fish throughout the year in the Sio River, and noticed that spawing started before the second rainfall peak. Fish from the Kagera matured at significantly larger sizes than fish from the Sio River. Male and female fish, from both rivers, fed intensively during the non-breeding months accumulating significant fat reserves; a probable energy storage mechanism prior to their spawning migrations. The differences between the populations is probably a phenotypic response to differing abiotic factors such as river size, flow velocity and food availability.     

Natural Colonization and Establishment of a Chinook Salmon, <Emphasis Type="Italic">Oncorhynchus tshawytscha</Emphasis>, Population in the Santa Cruz River,an Atlantic Basin of Patagonia

Synopsis We report the finding of an established population of exotic Chinook salmon spawning in headwaters of the Santa Cruz River system (Argentina), the first for this species in an Atlantic basin of South America. Spawning takes place in the Caterina River, a small tributary of Lake Argentino, located 488.5 km from the ocean. Anadromy was verified by correspondence of N and C stable isotope ratios with those of fish captured by bottom-trawlers in the ocean and those of anadromous rainbow trout from the same river basin. The scale patterns of most fish examined were consistent with a stream-type life cycle (i.e., seaward migration by juveniles after a full year in fresh water). Two potential origins were identified for this population: in situ introductions of fish imported directly from the USA in the early 20th century or fish from two ranching experiments conducted in southern Chile during the 1980s. In the latter case, colonization would have proceeded through the Strait of Magellan, helped by prevailing eastward currents.     

Migratory and reproductive behaviour of female adult Atlantic salmon, Salmo salar L., in a spawning stream

Migration and spawning behaviour of eight Atlantic salmon adult females were analysed by radio-tracking in relation to the degree of sexual maturity in a spawning tributary of the R. Sélune. Six of them were grilse and four of them were ripe. All the fish migrated upstream until reaching their spawning site at a distance of 4–12 km from the trap. The daily migration rate up to this site was inversely correlated with the length of the female. Spawning occurred in all fish at the same time when the water temperature increased dramatically. Spawning lasted 1–10 days according to the fish. After spawning, females quickly moved downstream only small distances and then stayed in approximately the same location until death. This study concluded that ripeness did not influence behaviour on the spawning migration and describes certain characteristics of the reproductive phase in a spawning tributary.     

Thermal heterogeneity,migration, and consequences for spawning potential of female bull trout in a river–reservoir system

The likelihood that fish will initiate spawning, spawn successfully, or skip spawning in a given year is conditioned in part on availability of energy reserves. We evaluated the consequences of spatial heterogeneity in thermal conditions on the energy accumulation and spawning potential of migratory bull trout (Salvelinus confluentus) in a regulated river–reservoir system. Based on existing data, we identified a portfolio of thermal exposures and migratory patterns and then estimated their influence on energy reserves of female bull trout with a bioenergetics model. Spawning by females was assumed to be possible if postspawning energy reserves equaled or exceeded 4 kJ/g. Given this assumption, results suggested up to 70% of the simulated fish could spawn each year. Fish that moved seasonally between a cold river segment and a warmer reservoir downstream had a greater growth rate and higher propensity to spawn in a given year (range: 40%–70%) compared with fish that resided solely in the cold river segment (25%–40%). On average, fish that spawned lost 30% of their energy content relative to their prespawn energy. In contrast, fish that skipped spawning accumulated, on average, 16% energy gains that could be used toward future gamete production. Skipped spawning occurred when water temperatures were relatively low or high, and if upstream migration occurred relatively late (mid‐July or later) or early (early‐May or earlier). Overall, our modeling effort suggests the configuration of thermal exposures, and the ability of bull trout to exploit this spatially and temporally variable thermal conditions can strongly influence energy reserves and likelihood of successful spawning.     

Spawning seasonality and body sizes at sexual maturity in the bluespine unicornfish,Naso unicornis (Acanthuridae)

We herein evaluate several reproductive metrics of Hawaiian Archipelagic populations of the bluespine unicornfish (Naso unicornis), an economically and ecologically important, broadly distributed tropical Pacific reef fish, based on multi-year, fishery-dependent and fishery-independent collections. Sex-specific spawning seasonality was characterized for fish collected mostly from Oahu (Main Hawaiian Islands, MHI) using a gonadosomatic index. Histological slides preparations were used to score gonad developmental phase and to classify individuals of either sex as immature or mature. Sex-specific median body lengths at maturity (L₅₀) were estimated by logistic fits of proportion mature versus length class. Spawning was highly seasonal in Hawaii, with a single brief (May–June) peak spawning period. Proportionate gonad-to-body weight values were relatively low, averaging only about 0.1 % and 0.6 % across all months of year and 0.16 % and 1.03 % during May–June for males and females, respectively. Median lengths at sexual maturity differed between the sexes. L₅₀ values for fish collected throughout all months of year were 30.1 ± 0.5 (standard error) cm Fork Length (FL) for males and 35.5 ± 0.7 cm FL for females. Spawning seasonality and L₅₀ estimates for bluespine unicornfish in Hawaii suggest that the species spawns several months earlier in the calendar year and matures at larger body lengths in Hawaii versus Guam, the Northern Mariana Islands, and Pohnpei in the Federated States of Micronesia. Estimated lengths at sexual maturity are compared to the minimum length (14 inches or 35.6 cm FL) mandated for this species in Hawaii: median size at maturity occurs at a length appreciably less than (males) or approximately equal to (females) minimum legal size. A likely disproportionately large contribution of old females to population replenishment is discussed relative to the minimum size limit.     

The biology of solenette, Buglossidium luteum (Risso), in the Solway Firth

The population of solenette, Buglossidium luteum , in the Solway Firth was studied from November 1977 until January 1979. The fish live in mobile, highly aggregated groupings, on sandy bottoms, in the outer Firth. A general offshore movement occurs in winter with a limited incursion of juveniles into the inner Solway in summer. Most growth occurs in the first few years of life and a length of 130 mm is attained. Longevity is 10 years. Females grow larger than males, but both sexes mature in their third year. Spawning starts in March/April, is most active in May/June and ends in August. Food intake is markedly reduced in winter. Small Crustacea, bivalve molluscs and polychaete worms form year-round components of a varied diet. Juvenile forms, especially shrimp and fish are readily taken when available.     

The biology of Fries' goby, Lesueurigobius friesii (Malm), in the Firth of Clyde, Scotland, and a comparison with other stocks

The general biology of a population of Lesueurigobius friesii in the Firth of Clyde, Scotland, was studied between October 1977 and December 1979. In this population the fish attained 95 mm and lived a maximum of nine years. The population growth characteristics from von Bertalanffy growth curves showed that the Clyde stock of L. friesii attained a greater maximum theoretical length (L∞) than stocks in the Lynn of Lorne or Biscay and had a lower growth coefficient ( K ). In all three stocks, the majority of the growth in length ( A _0.95) was achieved by the end of the fourth year of life. In general the sex ratio was 1: 1 throughout the season. Spawning occurred from May to August, approximately the same time as the Lynn of Lorne stock. Sexual maturity was first reached at a smaller size in males than females. The abundance of L. friesii in the Clyde fluctuated considerably with reduced numbers of fish caught just after spawning.     

Variation with age in the timing and duration of spawning in American plaice

Spawning time of female American plaice Hippoglossoides platessoides varied significantly with age. This effect, however, was not consistent across years. Generally, younger fish spawned earlier than older fish, but in the 1990s they spawned later than older fish. Spawning duration also varied with age, with younger fish generally having a longer spawning period than older fish. Changes in depth distribution were related to changes in both spawning time and duration. As depth increased, spawning time became later and duration became shorter. Fish <11 years old showed the largest change in both spawning time and depth distribution.     

Reproductive behavior of the halfmoon grouper, <Emphasis Type="Italic">Epinephelus rivulatus</Emphasis>, at Ningaloo Reef,Western Australia

Behaviors associated with spawning by the halfmoon grouper, Epinephelus rivulatus, at Ningaloo Reef, Western Australia, are described from in situ observations made each evening throughout most of a lunar cycle. Spawning occurred after sunset on six consecutive evenings during the full moon period. During this time males were particularly aggressive toward one another and maintained high levels of activity among the gravid females that rested within each of their territories. Spawning occurred when a male swam alongside a responsive female and the pair rose in a tight spiral 1–1.5 m into the water column before releasing gametes and returning to the seabed. Spawning activity was followed by a longer nonspawning period (ca. 20 days), when fewer intraspecific interactions were observed and gamete reserves were replenished. Histological and behavioral evidence suggests that this cycle of spawning and replenishment may occur on a monthly basis. Although individual fish, particularly females, moved into certain areas to spawn, E. rivulatus did not form spawning aggregations as do larger species of grouper.     

Age, growth, sexual maturity and food composition of Sciaena umbra in the south-eastern Black Sea, Turkey

Studied were the age, growth, maturity and food composition of the brown meager, Sciaena umbra, caught off Trabzon, south-eastern Black Sea (Turkey) in 2002–2003. A total of 329 individuals was collected by spear fishing and hand nets. The thin sectioning method was used for aging the fish otoliths. Fitted von Bertalanffy growth parameters for all fish were: L _∞ = 51.14 (±1.19) cm, k  =   0.27 (±0.02) year⁻¹ and t ₀ = −0.93 (±0.07) year. This study revealed that S. umbra is a relatively slow-growing and long-lived species with a life span in excess of 18 years. Sexual maturity begins when they reach a length of about 15 cm. Lengths at which 50% of brown meagre become mature are 19.50 for males and about 22 cm for females. Spawning begins in June, when the temperature is approximately 18°C, and ends in August. Gut content analysis indicated that this species feeds mainly on crustaceans, then switches to fish as they grow. Sciaena umbra appears to be an apex predator in the upper littoral zone.     

Seasonal Distribution of Antlered Sculpin, <Emphasis Type="Italic">Enophrys diceraus</Emphasis> (Cottidae) in Peter the Great Bay,Sea of Japan

The antlered sculpin Enophrys diceraus in Peter the Great Bay is found to inhabit from shallow waters to depths deeper than 600 m. The range of depth where this species occurs is the narrowest, from 12 to 250 m deep, in summer. The greatest depths of inhabitation are characteristic, in all seasons, only of adult fish of this species. In the cold period of the year, the young probably avoid the upper part of the shelf where the temperatures have cooled down to negative numbers. Spawning in the antlered sculpin begins in the second half of November. Females dominate the population of this species inhabiting Peter the Great Bay. Males reach 38 cm long and more; females can be up to 31 cm long. The greatest density of antlered sculpin in the summer period on the preferred substrates is observed in the western part of the bay, primarily on sandy ground.     

Population structure, reproduction and sex-change in a tropical East Atlantic grouper

Spawning time and sizes at first sexual maturity and at sex-reversal are described in the tropical blue-spotted grouper Cephalopholis taeniops . All juvenile fish possess non-functional ovaries. At sexual maturity, most juvenile fish become functional females. Some of these later change sex to become males. The remaining juvenile females change immediately to males, without time as functional females. This is a new scheme for sexual differentiation of groupers.     

The length weight relationship, age, growth and reproduction of the roach Rutilus rutilus (L.) in Lake Volvi

The length-weight relationship of a sample of 233 roach ( Rutilus rutilus ) can be described by the following equations: y =0·0356 x ^3·405 and y =0·0215 ×^3·606 for males and females respectively. In both equations y equals the body weight in grams and × is the standard length in centimetres. The average condition factor K was 2·01 with a range of 1·71 to 2·26. The roach's span of life was 13 years for both sexes. The growth increment is greater during the first year of life (about 56 mm), decreasing to approximately 17 mm at the end of the sixth year of life and then becoming constant at about 12 mm per year. Roach become sexually mature at age 1 + for males and one year later for females. The mean absolute fecundity was 9294 eggs; with a range from 920 to 32 810. The growth of the gonads is related to the age of the fish. Spawning occurs during the first half of April, at a mean water temperature of 10° C.     

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.     

The movements of brown trout, Salmo trutta (L.) in Loch Leven, Kinross, Scotland

Juvenile trout enter Loch Leven during autumn and winter from the nursery streams, spend their adolescent phase offshore until reaching a length of 0.30 cm, and then move to the littoral areas in early summer. There are two types of littoral area:'favourable'areas from which movement of individual fish in the summer is very restricted, and'unfavourable'areas used briefly in early summer from which movement away is pronounced. Trout are absent from the littoral areas in winter. In subsequent summers homing to previous feeding areas is characteristic of fish from'favourable'areas, with a tendency for older fish to move to the south east area of the loch. Spawning runs occur simultaneously into the main inflows, chiefly between October and December. Emigration into the outflow occurs, but is probably unimportant.     

Reproductive strategy and interspecific competition in the Lake-living gobiid fish isaza,Chaenogobius isaza

Isaza,Chaenogobius isaza, is a small gobiid fish endemic to Lake Biwa. It lives offshore throughout almost the entire year, showing a remarkable diel vertical migration. In early spring, males and females migrate to lake shore to spawn under stones. Spawning season is limited to a very short span of time in early spring, late April to early May. During this short spawning season, the male is supposed to have only 2 brood cycles at maximum. At each brood cycle, the male is strictly monogynous, never accepting additional females. Males therefore show a marked mate choice, choosing a larger female regardless of the size of the male himself. Females also choose larger males. However, males are supposed to not waste time in male-male fighting in the natural spawning area. That this very short spawning season and its occurrence in early spring is primarily to avoid interspecific competition with another littorally reproducing goby Yoshinobori,Rhinogobius brunneus, is experimentally demonstrated.