Age,growth, and reproductive biology of blacktail snapper,Lutjanus fulvus,around the Yaeyama Islands,Okinawa, Japan

Age, growth, and reproductive characteristics of blacktail snapper, Lutjanus fulvus, which is a commercial fish species, were investigated using 322 specimens (40–332 mm in fork length) caught around the Yaeyama Islands, Okinawa, Japan. Spawning season was estimated to be from April to October, and spawning was confirmed around the full moon and the last quarter moon. Age determination using sectioned otoliths revealed that ages ranged from 0 to 34 years and the majority was ≥ 3 years. Parameters of the von Bertalanffy growth function were estimated to be L _∞  = 270 mm, k = 0.40, and t ₀  = ?0.48 years for females, and 257 mm, 0.44, and ?0.42 years for males. Initial growth was rapid during the first 3 years, attaining over 200 mm for both sexes, and then females grew larger than males. Sizes (ages) at the first sexual maturity were 225 mm (4 years) for females and 207 mm (3 years) for males. The wide range of age composition in catch with majority of ≥3 years old implied that the current fishing effort to harvest was not sufficiently large enough to collapse the stock immediately.     

Age and growth of longnose trevally (Carangoides chrysophrys) in the Arabian Sea

The ages and growth of longnose trevally (Carangoides chrysophrys), caught in the northwest Arabian Sea between April 2005 and September 2006, were investigated. Age and growth of 336 fish specimens were determined using sectioned sagittae otoliths. Annual opaque growth rings were formed between December and March, with the majority being laid down in February and March, coinciding with the spawning period and high water temperatures. Marginal zone or edge analysis was used to validate the annual deposition of the opaque zone in the otoliths. This species showed large variations in length‐at‐age, suggesting large growth variations among individuals of the same cohort. The estimated von Bertalanffy growth model differed significantly between the sexes, with males having larger mean lengths at age and reaching a larger asymptotic size. The von Bertalanffy growth models were TL (cm) = 73.34[1‐exp (?0.25 (t + 1.21))] and TL(cm) = 73.26[1‐exp (?0.24 (t + 1.20))] for males and females, respectively.     

Aspects of the biology of Scomberomorus maculatus (Mitchill) in Trinidad

A study was made of the biology of S. maculatus . Results of gonadal examination of 347 males and 409 females suggest spawning takes place from October to April, a period associated with low salinities. First spawning takes place at ages I1 and/or III for both sexes. Sex ratio results suggest spawning may be promiscuous, males outnumbering females. Egg counts from 12 ripe females ranged from 26 057 to 149 736. A period of abundance from May to September may be associated with a post-spawning feeding migration encompassing the island, possibly in a clockwise direction. Otolith were used to age 817 fish. Opaque and translucent rings are formed yearly. The translucent ring, representing a period of slow growth, is laid down during the spawning season. The fish can live for nine years with females growing faster than males. Growth parameters are compared with those obtained for Brazilian and Florida fish. Mortality rates were investigated and gill nets effected higher mortality rates than beach seines. Full recruitment takes place at age III for gill nets, and ages II and III for beach seines.     

A note on growth and mortality of trout, Salmo trutta L., in afferent streams of Windermere

Trout were sampled in six afferent streams of Windermere during the spawning season. The main migration of adult trout into the streams took place during early November. Length-weight relationships and scale-fish length relationships are given. There was no significant difference in length for age or sex between cohorts within streams. Three groups of fish could be identified depending on whether the fish entered the lake at 1+, 2+, or 3+ years. The percentage number of the population entering the lake at each of these ages was 16, 70 and 14%, respectively. After the fish had migrated from the streams their growth in length fitted the von Bertalanffy growth model. Fish entering the lake at 1+ and 2+ years had similar A.95 values (6·31 and 6·97 years) as the latter grew slightly faster in the lake. Those entering the lake at 3+ years grew at a slower rate to the other two groups but achieved a longer ultimate length. Faster growing fish had higher instantaneous mortality rates. Twenty-eight to 29% of the males remaining in the stream at 1+ years became sexually mature. Faster growing females became sexually mature earlier. Only those fish which entered the lake at 1+ years grew close, during their early years before sexual maturity, to the theoretical maximum given by Elliott's model.     

Reproduction and development of the weakly electric fish,Pollimyrus isidori (Mormyridae,Teleostei) in captivity

Synopsis No clear sexual dimorphism occurs in Pollimyrus isidori. Females usually grew slightly larger than males. The anal-fin reflex, however, makes it easy to discriminate between males and females. Spawning took place during the first six hours of the dark phase, in the territory of the male. During each spawning act 2–4 eggs were laid. The male put the eggs into a well-hidden nest previously constructed from plant material. The eggs, free embryos, and larvae of several spawnings were guarded by the male for several weeks. The females laid on average 120 eggs per fractional spawning. The eggs were 2 mm in diameter, not adhesive and very yolky. There was a relationship between pH and viability (% embryos hatched). Hatching occurred on the third day after spawning. The respiratory network of segmental origin in the median fin fold was well developed in the free embryos. Transition to exogenous feeding occurred on day 14. The larval period ended when the fish were 15 mm long and 40–50 days old. First gonadal recrudescence occurred at a total length of 6 cm (about 200 days old). The environmental factors decreasing conductivity and pH, increasing water level, and imitation of rain led to gonadal recrudescence, but pH did not act as a cue. Recrudescence was triggered by a decrease of conductivity, but absolute values or ionic composition of the water were not important. Maturation was completed after about fifty days. Mature and spawning fish no longer required any variation of these environmental factors to maintain mature gonads. A steady and considerable increase in conductivity led to gonadal regression. The fish did not show postbreeding refractoriness.     

Life-history traits of the endangered river blenny Salaria fluviatilis (Asso) and their implications for conservation

The life-history characteristics of the river blenny Salaria fluviatilis in a Mediterranean stream in north-east Spain have been studied. The maximum age observed was 4+ years in both sexes, although only age groups 0+ and 1+ years were well represented. For both sexes, growth was rapid between April and June (before the summer drought) and in October. The instantaneous rate of monthly growth (April to October) was positively correlated with water depth. All fish attained sexual maturity during their first year of life. Females spawned multiple times. Spawning occurred mainly from June to August, although older females (2+ years old) began in May. The relationship between fecundity and total length recorded for older females in the spring was not significantly different from that obtained for 1 year-old females in the summer. The mean diameter of ripe oocytes, however, was greater in older females. Larger eggs that were laid during a period of good food supply (spring) might have a higher probability of survival. The results suggest that female fecundity is affected by environmental conditions. The species is characterized by fast growth, early maturity, multiple spawning and limited longevity. This may be a good life-history strategy for small fish species in unstable environments, where adult mortality is high, variable or unpredictable. Some life-history traits of the river blenny suggest that this species might be vulnerable to more severe drought conditions than those associated with the Mediterranean climate.     

Demographic Structure,Sex Ratio and Growth Rates of Southern Bluefin Tuna (Thunnus maccoyii) on the Spawning Ground

The demographics of the southern bluefin tuna (SBT) Thunnus maccoyii spawning stock were examined through a large-scale monitoring program of the Indonesian longline catch on the spawning ground between 1995 and 2012. The size and age structure of the spawning population has undergone significant changes since monitoring began. There has been a reduction in the relative abundance of larger/older SBT in the catch since the early 2000s, and a corresponding decrease in mean length and age, but there was no evidence of a significant truncation of the age distribution. Pulses of young SBT appear in the catches in the early- and mid-2000s and may be the first evidence of increased recruitment into the spawning stock since 1995. Fish in these two recruitment pulses were spawned around 1991 and 1997. Size-related variations in sex ratio were also observed with female bias for fish less than 170 cm FL and male bias for fish greater than 170 cm FL. This trend of increasing proportion of males with size above 170 cm FL is likely to be related to sexual dimorphism in growth rates as male length-at-age is greater than that for females after age 10 years. Mean length-at-age of fish aged 8–10 years was greater for both males and females on the spawning ground than off the spawning ground, suggesting that size may be the dominant factor determining timing of maturation in SBT. In addition to these direct results, the data and samples from this program have been central to the assessment and management of this internationally harvested stock.     

Reproductive and feeding biology of the Natal mountain catfish, Amphilius natalensis (Siluriformes: Amphiliidae)

Aspects of the biology of the Natal mountain catfish, Amphilius natalensis, including gametogenesis, spawning season, size-at-maturity, sex ratio, diet and feeding morphology were determined from fish collected in the Songimvelo Game Reserve, South Africa, between 1989 and 1990. Female sexual maturity was established at 63 mm total length. A. natalensis is an asynchronous, iteroparous spawner, breeding throughout summer from August to February. Sex ratio of females to males was 2.2:1, with females attaining a significantly larger size than males. Gametogenesis followed a pattern similar to that of other freshwater teleosts peaking over the spawning period. Stomach content analysis and observations on feeding morphology revealed that A. natalensis was an opportunistic predator with large fish consuming larger prey from a greater variety of taxonomic groups. The most abundant prey items eaten were dipteran (particularly Chironomidae) and ephemeropteran (particularly Baetidae) larvae.     

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.     

Omitted spawning in compensatory-growing perch

Individual growth trajectories of perch Perca fluviatilis in a Swedish forest lake (sampled in March) revealed growth depression at intermediate sizes, followed by enhanced, compensatory growth at larger sizes. All males of age ≥3+ years had mature, almost ripe testes. The proportion of spawning females was higher at age 3+ years (79%) than at older ages (44%), indicating that older females with non-developing ovaries were resting rather than immature juveniles. Resting females were 175–247 mm in total length ( L _T), and they were usually in a state of increasing annual growth. Spawning females were of more variable size (123–418 mm), and the larger ones had entered the faster growing state ≥2+ years before catch. Detectable growth costs of spawning indicated that resting females made a trade-off between current and future reproduction, rather than being constrained by poor feeding conditions.     

Annual cycles of growth and reproduction in hatchery–reared Florida largemouth bass, Micropterus salmoides floridanus, raised on forage or pelleted diets

Annual cycles of growth and reproduction of hatchery–reared Florida largemouth bass, Micropterus salmoides floridanus , were investigated. Animals were raised on either forage (goldfish, Carassius auratus ) or a pelleted salmon feed. Male and female year–class 1 largemouth bass were sampled throughout one complete yearly cycle (January–December). A biphasic growth cycle was observed in both forage–fed and pellet–fed fish. No increase in body length or weight was observed until approximately midway through the spawning period (May), after which fish grew at a consistent rate for the remainder of the study. The reproductive cycle of forage–fed fish was characterized by a rapid increase in gonadosomatic index (GS1) between January and April, followed by a prolonged spawning period (April–July) during which GSI progressively declined. Fully regressed gonads were observed in September and October, and a resumption of gonadal recrudescence was observed between October and December. Visceral adipose deposits (expressed as mesenteric fat index; MFI) were resorbed during gonadal growth and the initial stages of the spawning period, and restored during the post–spawning phase. Fish raised on pelleted feed had growth and reproductive cycles that parallelled those of forage–fed fish, but several significant differences were observed between the two diet groups. During the growth phase of the cycle, pellet–fed largemouth bass grew significantly faster than forage–fed largemouth bass, and had significantly larger MFIs than forage–fed largemouth bass at all times of the year. Pellet–fed fish also had significantly larger GSIs than forage–fed fish. These data indicate that diet composition may be an important determinant of growth and reproductive function in this species.     

Life-history traits of Amur sleeper, <Emphasis Type="Italic">Perccottus glenii</Emphasis>, in the invaded Vistula River: early investment in reproduction but reduced growth rate

In recent decades, Amur sleeper is one of the most invasive fish species in Eastern and Central Europe. Generally, it is assumed that success of an invasive species can largely depend on the plasticity of its life-history traits, e.g., indicated by higher investment in reproduction in the initial stage of its invasion. On the other hand, such energy allocation to production of gonads should negatively impact somatic growth rate. The aim of this article was to explore this phenomenon in a non-native population of Amur sleeper inhabiting artificial reservoir on a large lowland river in Central Europe. Through analysis of the population age structure, sex-dependent growth rate and life-history traits we assessed investment in reproduction and its possible relationship with growth pattern as well as compared the results with literature data from native and introduced range. Samples collected monthly from April 2005 to March 2006 were used to estimate sex ratio, GSI, fecundity, eggs diameter frequency over the year, duration of spawning season, and mode of spawning. Age structure was calculated from scales and the same data were also used to back-calculate standard length (SL) at age. The population in the Włocławski Reservoir was represented by eight age groups, and its life span was one of the longest recorded both in its natural range and introduced areas. The weight–length relationship showed that the Amur sleeper grew isometrically and there was no difference between females and males. Although the Amur sleeper growth rate was relatively slow in the Włocławski Reservoir, its increment in the first year of life was comparable to that in other introduced areas and higher than in its natural range. The female age of maturation (1+) found in the reservoir was earlier than observed in its natural range as well as in most introduced areas (2+, 3+). Female length at maturation was similar to that reported elsewhere. The back-calculated standard length (SL) of females and males showed that in the first two age classes (1 and 2) males achieved larger SL than females. Meanwhile, at age 3, 4 and 5, females were larger than males but these differences were insignificant, except for class 5. For both sexes the average annual increment of SL decreased with age but in females the increment was always higher than in males (P < 0.05). The growth rate differences between females and males resulted possibly from their unequal investment in reproduction. Multiple spawning in the Włocławski Reservoir lasted from April to the end of August and was almost 3 months longer than in other regions. Thus, this higher investment in reproduction displayed by, e.g., earlier maturation of females and longer spawning season in the Włocławski Reservoir, may contribute to invasive success of Amur sleeper in newly colonized areas; however, the costs of this strategy result in slower growth in older age classes.     

Life history traits of Scardinius acarnanicus (Economidis, 1991) (Pisces: Cyprinidae) in two Greek lakes (Lysimachia and Trichonis)

Age, growth, reproduction and mortality of Scardinius acarnanicus, an endemic cyprinid fish from central and western Greece, were investigated in two contrasting environments, the eutrophic Lake Lysimachia and the oligotrophic to mesotrophic Lake Trichonis. Maximum ages observed were 7+ for males and 10+ for females in Lake Lysimachia and 8+ for males and females in Lake Trichonis. Scardinius acarnanicus grew allometrically (slope of fork length–somatic weight regressions >3) and relatively rapidly until age 2 or 3 years, then slowed at a time coincident with maturation. Total instantaneous mortality rates of fish from Lake Trichonis were higher than in Lake Lysimachia. Scardinius acarnanicus is a multiple spawner; monthly values of the gonadosomatic index (GSI) indicated that spawning occurred mainly in April. Mean egg diameter in Lake Lysimachia was 1.54 ± 0.2 and 1.28 ± 0.16 mm in Lake Thrichonis. In Lake Lysimachia, the population sex ratio departed markedly from 1 : 1; females were more abundant at ages >3 and the overall male : female ratio was 1 : 1.47. In Lake Trichonis, females were more abundant at ages >6; the overall male : female ratio was 1 : 1.16, not significantly different from a 1 : 1 ratio.     

Female-biased operational sex ratio of sexual host fish in a gynogenetic complex of Carassius auratus

To study the coexistence of sexual and gynogenetic forms, we examined the population structure of a gynogenetic complex of the Japanese crucian carp, Carassius auratus Temminck et Schlegel, during the April–June reproductive season by collecting 1225 mature fish that migrated from Lake Suwa to a tributary river for spawning. There were more sexual fish (about 80%) than gynogenetic fish in this complex, and the operational sex ratio in the sexual form was female biased (males were about 20%). Mean standard length and body weight of sexual females were larger than those of sexual males. Sex ratio was male biased in smaller fish (standard length, <8.5 cm) but female biased in larger fish (standard length, ≥8.5 cm). We determined age by scale ring marks; the average age of sexual females was higher than that of males, but there was no significant difference in the average age between sexual and gynogenetic females. Sex ratio in the sexual form was more female biased for old than for young fish, and the mean size of sexual females was larger than that of males of the same age. The clear female-biased sex ratio and age difference between sexual females and males can be explained either by (1) higher mortality of males or by (2) female-biased sex allocation. The latter process reduces the disadvantage of sex and contributes to the coexistence of sexual and gynogenetic forms. Received: November 24, 2000 / Accepted: March 6, 2001     

Aspects of the biology of the spotted dragonet Callionymus maculatus Rafmesque-Schmaltz from the west coast of Scotland

The biology of a Scottish population of the spotted dragonet Callionymus maculatus was studied from February 1975 to September 1976. The data were taken from monthly samples totalling over 700 fish trawled in 18–36 m on a soft mud bottom. Neither otoliths nor radial bones were found to be suitable for age determination, but evidence from other sources suggested that most growth takes place in the first two years of life and that males grow faster, but do not live as long (at least 3 years) as females (at least 5 years). Examination of the gonads showed that the spawning season probably lasts from April to September, that females mature earlier in life than males and are serial spawners. The males may reach first maturity at different ages. The sexes are markedly dimorphic. The rays of the dorsal, anal and caudal fins grow isometrically in females but growth of these organs in males is allo-metric after maturity has been achieved. The fish feeds predominantly on polychaetes and amphipods, although bivalve molluscs, macruran decapods and ophiuroids also occur frequently in its diet. There is some difference in the diet between length classes, smaller fish taking fewer polychaetes and more amphipods than the larger individuals. The species is finally compared with other dragonets whose biology is known.     

Observations on the biology of the perch, Perca fluviatilis, in the River Stour, Dorset

SUMMARY. Opercular bones from 323 perch from the River Stour were used for age and back-calculated growth determinations. Annuli were formed during May at the beginning of the growth period. Growth was minimal from October to April. Female perch grew faster than males, and the growth rates of both sexes were higher than those observed in most other European waters. Spawning occurred during late April and early May; male gonads began development in August and had attained their maximum weight in September, but the ovaries developed gradually from August until April. Immature perch had an annual cycle of condition with a maximum in June-July and a minimum in December-January. The condition of mature males and females was affected by the gonad cycle. The fecundity of Stour perch is expressed by the formula: log egg number = 2.40 log length (mm) - 1.34.
Approximately 25% of males were mature at age I and all were mature at age II, whereas most females did not spawn until age III. Ephemeroptera nymphs and minnow fry constituted the bulk of the diet of 0-group perch; Ephemeroptera nymphs, minnow fry and Corixidae were the most numerous items in I group perch, whereas older perch contained Corixidae and a wider range of fish prey species, although minnows were the most numerous of these.     

Age estimation,growth and maturity of the Argentine hake (Merluccius hubbsi Marini, 1933) along the northernmost limit of its distribution in the south-western Atlantic

Age, growth and length-at-maturity of the Argentine hake (Merluccius hubbsi) were studied in the northernmost limit of the species distribution in the south-western Atlantic. A total of 351 otoliths and information from 1610 specimens sampled from the industrial double-rig trawl landings between May 2013 and April 2014 were used. Age and growth were estimated by counting and measuring increments in sectioned sagittae otoliths, and length at maturity was estimated based on macroscopic gonadal analysis. For both sexes, hepatosomatic index and condition index increased mainly during spring, reaching a maximum at the end of summer before the subsequent spawning season began. Gonadosomatic index was highest in April, believed to correspond with peak spawning. The annual periodicity of alternate opaque and translucent zones was validated by marginal increment analysis. Growth curves were fitted to back-calculated size at age by fitting the three-parameters von Bertalanffy growth function. The maximum age was 5 years in fish of either sex. Females attained larger sizes than males. The parameters of the von Bertalanffy growth equations were: L∞?=?533?mm, k?=?0.231 year^?1 and t₀?=??0.935 year for females; L∞?=?394?mm, k?=?0.405 year^?1 and t₀?=??0.463 year for males. The mean length and age at first maturity was 273?mm at 1.9 years for males and 274?mm at 2.0 years for females.     

Age,growth, and age at sexual maturity of the commercially landed skate species,Dipturus chinensis (Basilewsky, 1855), in the northern East China Sea

Age, growth, and age at sexual maturity of the polkadot skate Dipturus chinensis, in the northern East China Sea were determined for a total of 614 specimens collected from April 2009 to December 2014. Vertebral centrum analysis was used to calculate the age of the skates. Annual band deposition was determined by marginal increment analysis. The von Bertalanffy growth model was fitted to the observed length‐at‐age data for each sex (males, L_∞ = 76.8, k = 0.109, t₀ = ?1.28; females, L_∞ = 83.1, k = 0.103, t₀ = ?1.20). Growth patterns of females and males were similar until the age of 6; thereafter, females grew larger than males. Maximum age recorded was 13 years for males and 15 years for females. Age at 50% sexual maturity was 8.22 years for males and 9.39 years for females. These results indicate that D. chinensis is slow growing, relatively long‐lived, and late maturing, and therefore vulnerable to exploitation.     

A population study of Barbus barbus L. in the River Severn, England

Scales from 7071 barbel from the River Severn were used for age and growth determinations. The scales showed clear annual checks which were laid in May when most fish spawned. Scale structure and length frequency distributions showed an almost total absence of 1968 year class barbel. Growth was significantly faster in some sections of the sampling area than in others. Back-calculated growth analysis showed a systematic decrease in length for each age for females and males in the 1961 to 1967 year classes. Females grew significantly faster than males after four years of age and reached greater ultimate size. There was a preponderance of males between the ages of III and VII and a dominance of females in older age groups. The overall sex ratio of males to females was 2–41: 1. A distinct seasonal growth pattern was shown.     

Reproductive cycles in a reared strain of the mummichog, a daily spawner

Annual, lunar, and diel samplings were taken from a strain of mummichog (Arasaki strain) reared in outdoor tanks under natural conditions, to examine gonadal maturity. Gonads of yearling fish were quite immature in September. During late autumn and winter, a gradual increase in the GSI of both sexes was observed, and the growth of cortical alveolus phase oocytes in females and basal spermatogenesis in males progressed. In late February, a rapid increase in the GSI of both sexes, vitellogenesis in females, and active spermatogenesis in males, occurred. The spawning period of the yearling fish was from late March to August judging from the presence of milt-producing males and ovulated females. The spawning period of the underyearling fish started in the same month as the yearlings, but terminated 1 month earlier. Plasma levels of oestradiol-17 β (E₂) in females and testosterone in males were high during the spawning period in the yearlings. In the underyearlings, however, E₂ levels peaked in early spring, and declined in the latter part of the spawning period. Neither a lunar nor semilunar cycle was evident in the reproductive activity of this fish, which proved to be a typical daily spawner. Females showed an apparent daily reproductive cycle; oocyte maturation commenced at about 1200 hours, germinal vesicle breakdown (GVBD) occurred at about 2400 hours, and ovulation was completed by 2400 hours, 24 h after GVBD. Such clear annual and daily reproductive cycles make this strain of mummichog a suitable model for the study of environmental and endocrine regulation of reproductive cycles in marine and estuarine teleosts.