Analysis of the hatching site and migratory behaviour of the swordtip squid (Uroteuthis edulis) caught in the Japan Sea and Tsushima Strait in autumn estimated by statolith analysis

In contrast to the swordtip squid (Uroteuthis edulis) caught in the spring and summer, those caught in the autumn in the Japan Sea and the Tsushima Strait are characterized by thick bodies with large clubs, long tentacles and large suckers. In addition, most females and many males are immature. However, the reasons for these characteristics, as well as the hatching site and migratory behaviour, are not well known. The empirical water temperature of juveniles was estimated at ～17°C through strontium:calcium (Sr:Ca) ratios in statoliths and information on seawater temperature distribution. The ontogenetic variation in Sr:Ca ratios decreased from hatching to 60 days after hatching and then remained stable. The estimated water temperature was ～21°C after 60 days. Thus, individuals of the autumn-migrating group most likely hatch in the southern East China Sea in the winter and early spring and then move north-eastwards with currents and pass through the Tsushima Strait into the southern Japan Sea during or after July. However, the squid could be present in these waters without strong currents northeast of Tsushima Island, where thermoclines occur during summer, and become confined in limited layers until vertical mixing occurs in the autumn. The distribution of the squid would thereafter extend to fishing grounds in the southern and south-eastern Japan Sea and then to the Tsushima Strait. This migratory behaviour could be the cause of the observed characteristics because bottom seawater temperatures are much lower in the Japan Sea than in the East China Sea.     

The population density, growth rate and production of roach Rutilus mtilus (L.) in Tjeukemeer, The Netherlands

A method of estimating the population density of roach in Tjeukemeer (21.3 km²) using 20 529 introduced fin-clipped fish is described. Fyke nets proved to be an effective method of sampling the population for marked fish during the spawning season. A total of 20 277 roach were processed during the recapturing period. The population density of roach (⋝ 14 cm) was estimated to be 1 246 458. The growth rate of roach in the lake although relatively poor (von Bertalanffy's L ∞ for males and females, 22 and 26 cm respectively) for the species was similar to that recorded in three other Friesian lakes. The mortality rate of males was higher than that of females. Logarithmic length-weight regression analyses showed that the value of the coefficient varied both within and between the sexes, that of females being higher (range 3.03–3.375) than that of males (range 2.76–3.254). Seasonal changes in the size of the coefficient were due to a disproportionate loss of gonad weight in larger fish. The fecundity of the population was comparatively high for the species.
The total production of the population was estimated to be 95 hg ha⁻¹ of which 39 kg ha⁻¹ was contributed by fry. In older (⋝ IV) fish the production of females (12 kg ha⁻¹) exceeded that (2 kg ha⁻¹) of males, due to differences in their growth and mortality rates. The relatively poor performance of roach in Tjeukemeer, in terms of biomass and production was due to a scarcity of zoobenthos and competition from other species offish. There is no evidence either from this study or the literature that the productive potential of roach in lakes is high, even though macrophytes and detritus can be consumed in significant amounts.     

The growth of charr, Salvelinus willughbii Günther, in Windermere

The growth of charr ( Salvelinus willughbii Günther ) caught in Windermere from 1941–1952 has been studied. Scales were used for determination of age and back-calculation of length for age. Autumn and spring spawners, males and females, and charr of normal and dwarf growth were treated separately. In fish of normal growth, the spring spawners were significantly smaller than the autumn spawners at ages 1 and 2 years, and significantly larger from age 4 years onwards. There was little difference in growth between males and females within the two spawning populations. Charr of lengths of less than 200 mm at age 4 years were considered to be dwarfs. Mean lengths at capture of male charr were: autumn spawners normal growth 272 mm, dwarf 218 mm; spring spawners normal growth 327 mm, dwarf 194 mm. The oldest recorded age was 8 years.     

Biology of the western minnow,Galaxias occidentalis Ogilby (Teleostei : Galaxiidae), in a south-western Australian river

The size and age composition, growth and diet of the western minnow, Galaxias occidentalis, in the southern branch of the Collie River in south-western Australia were determined from samples collected at approximately monthly intervals between January 1984 and December 1986. The prominent, narrow hyaline zone on otoliths was shown to be formed annually and thus valid for ageing these fish. An examination of the otoliths of 4711 fish indicated that 69.2 and 26.8% of the fish caught belonged to the 0 + and I + age classes, respectively. While the vast majority of the remaining fish represented the II + age class, a few III + and IV + and one V + fish were also recorded. Growth was seasonal, being greatest in spring and autumn and effectively ceasing in winter. Females began to grow faster than males during their first autumn of life. The respective mean lengths of males and females were 70 and 75 mm at the end of the first year and 90 and 100 mm at the end of the second year. The largest fish caught was a III + female measuring 163 mm and weighing 32.0 g. The respective von Bertalanffy growth curve parameters for L, K and t₀ were 109, 0.758 and - 0.338 for males, and 124, 0.762 and - 0.223 for females. Although the diet of G. occidentalis was always dominated by small terrestrial fauna, and particularly insects, conspicuous seasonal differences were found between the more important of the other components. Data on body size, growth and diet of G. occidentalis are compared with those recorded for other galaxiids.     

An examination of the fish population in the River Trent, Nottinghamshire using angler catches

During this study, anglers caught over 580 kg of fish, comprising over 29 500 individuals of 14 species. Nine times as many gudgeon, Gobio gobio , as roach, Rutilus rutilus , were caught. Gudgeon represented 35.94% of the total catch weight compared with 44.64% for roach. The mean total catch per man-hour was 8.9 fish and the mean catch rate was 176 g per man-hour. Population estimates for fish longer than 12 cm for all species other than gudgeon and bleak, Alburnus alburnus , gave fish densities of 0.21 fish m⁻², the roach population was 0.15 m⁻², and that for dace Leuciscus leuciscus , 0.02 m⁻². The population density for all sizes of all species caught was estimated to be 2.25 fish m⁻².
The fish biomass available to the angler was 447 kg ha⁻². The rate of exploitation of the fishery over the period of sampling was high at 17%, representing an annual exploitation rate of 94%.     

Seasonal population dynamics of Pallisentis (Neosentis) celatus (Acanthocephala: Quadrigyridae) in the intestine of the rice-field eel Monopterus albus in China

Studies on the seasonal population dynamics of Pallisentis (Neosentis) celatus (Acanthocephala: Quadrigyridae) in the intestine of the rice-field eel Monopterus albus from the paddies and ditches in the Dong-ting Lake basin of China, were carried out with samples taken from June 2002 to May 2003. Prevalences were above 21% in all seasons sampled and with a distinct seasonal trend, which was highest (45.81%) in the spring and decreased by degrees. The mean intensity of infection was above 4.0 worms per fish. The maximum intensity of worms recovered from a single fish was 86 in the autumn of 2002. No significant seasonal differences were found in mean intensities, and differences in the mean abundance between winter and spring, winter and autumn were significant. Over-dispersed distributions of P. (N.) celatus in the host population, due to heterogeneity and feeding habits, were observed in all seasons. The size composition of both sexes of P. (N.) celatus showed males between 2.0 mm and 14.0 mm and females between 2.2 mm and 22.2 mm, with the main recruitment phase in the worm populations occurring in the summer and autumn, especially in the autumn, with the lowest recruitment occurring in the winter. The maturation and copulation of worms were mainly focused in the spring season. The sex ratio of female to male was both high in summer (1.09:1) and autumn (1.08:1). The higher proportion of females and the change in the worm sex ratio in summer can be attributed to the reduced longevity of male worms. As immature male worms exhibit a higher proportion of the worm population than females in all seasons, further studies are needed to determine if such a situation compensates for the shorter life span of males.     

Sex identification and PIT‐tagging: tools and prospects for studying intersexual differences in freshwater fishes

This study evaluated a technique to allow the long‐term monitoring of individual fishes of known sex in the wild using sex confirmation in close proximity to the reproductive period combined with individual tagging. Hundreds of partially migratory roach Rutilus rutilus were tagged with passive integrated transponders (PIT) following sex determination in spring and various performance measures were compared with fish tagged outside the reproductive period in autumn. Short‐term survival was >95% for R. rutilus sexed and tagged under natural field conditions. Total length (L_T) did not affect the probability of survival within the size range tagged (119–280 mm), nor were there differences in timing of migration the following season between individuals sexed and tagged in spring and individuals tagged in autumn (i.e. outside the reproductive period). Also, a similar per cent of R. rutilus sexed and tagged in spring and tagged in autumn migrated the following season (34·5 and 34·7%). Moreover, long‐term recapture data revealed no significant differences in body condition between R. rutilus individuals sexed and tagged in spring, individuals tagged in autumn and unmanipulated individuals. The observed sex ratio of recaptured fish did not differ from the expected values of equal recapture rates between males and females. Hence, there is no observable evidence for an adverse effect of tagging close to the reproductive period and therefore this method is suitable for studying intersexual differences and other phenotypic traits temporarily expressed during reproduction at the individual level in fishes.     

Differences in the condition of Norway lobsters (Nephrops norvegicus (L.)) from trawled and creeled fishing areas

The condition of trawled and creeled Norway lobsters, Nephrops norvegicus, was compared in individuals caught along the Swedish west coast. Female and male N. norvegicus were collected from trawled and creeled areas in the spring and autumn. Their nutritional state was determined by analysing individuals for haemocyanin concentration, the dry weight/wet weight relationship in muscle and hepatopancreas and the percentage dry weight of muscle and hepatopancreas of total animal dry weight. All parameters were measured on an individual basis and checked for size dependence. Creeled individuals were generally found to be in better condition than individuals from trawled areas, and animal condition increased from spring to autumn. Autumn males from creeled sites were overall in the best condition, having the highest mean haemocyanin concentration, muscle and hepatopancreas dry weight/wet weight relationship and percentage dry weight of muscle tissue. Claw symmetry (paired cutters) was suggested as an indicator of limb loss, with the highest occurrence found in females from trawled sites. Crusher absence had no effect on the animal's individual percentage dry weight of muscle, although the mean was lower in trawled females than in other groups. Resource limitation and physical stress are discussed as possible underlying factors affecting the observed differences.     

Diet and growth of asp,Aspius aspius (Linnaeus, 1758), in the Danube River near the confluence with the Sava River (Serbia)

A sample of 198 asp (Aspius aspius) was collected over a 28.5 km long section of the Danube River, upstream and downstream from the mouth of the Sava River, in order to provide information on population structure, diet, growth, and condition of this species. Total body lengths of sampled fish were 90–405 mm, and body weights 5–567 g. The sample was predominantly sub‐adult fish aged 0+ to 4+ years. Sexually immature asp prevailed over the sexually mature asp. The sex ratio (1.4 : 1) was biased toward males. Male asps in the Danube become sexually mature only in their fifth year of life, and the females even later, as no sexually mature females were caught. The diet spectrum consists exclusively of fishes; of seven determined prey species, most important are bleak Alburnus alburnus, roach Rutilus rutilus, and goldfish Carassius auratus. Highest value of the seasonal vacuity index is in November (I_v = 94.1), and the smallest in July (I_v = 35.6). Trophic niche breadth is largest in May (H = 1.40), and smallest in November (H = 0.00). The largest average number of prey items is found in age class 4+ (2.33), the smallest in age class 0+ (1.00). Von Bertalanffy growth parameters are L_∞ = 526.46, K = 0.28, and t₀ = 0.22. The length–weight relationship is described as log W = ?5.16 + 3.03 log L. Fulton’s condition factor increases with fish length, from 0.70 to 0.83. Regarding seasonal fluctuations, this factor begins to increase in late spring, with the trend continuing until autumn, and then decreasing from autumn to spring.     

Age and growth analysis of the mosshead sculpin Clinocottus globiceps Girard 1857 (Pisces: Cottidae) from Helby Island, British Columbia

The age and growth of the cottid fish Clinocottus globiceps Girard from tidepools at Helby Island, British Columbia, Canada were investigated with the aid of whole saccular otoliths (sagittae); ages were validated by marginal increment analysis. Four hundred and twenty five specimens were examined from 214 females and 211 males. Marginal increment analysis on specimens with one to three opaque zones suggested an annual ring deposition in sagittae during the late autumn and spring months.
The C. globiceps population was composed of individuals from less than 1 year to 5 years of age for fish measuring between 5–120 mm standard length. Growth was faster for younger than for older age groups. Lengths-at-age data were fitted to the Gompertz growth model, and estimates of the model parameters L₀, G and g were 26.7 mm 1.58 and 0.30 for pooled cohorts, respectively. The highest levels of growth occurred during late spring and early summer, when water temperatures were at maximum and food was most abundant. The lowest levels of growth occurred during the autumn and winter months.     

Age, growth and reproduction of the cyprinid Rutilus lemmingii (Steindachner, 1866) in the River Huebra, Central Spain

Age, growth and reproduction of the R. lemmingii population of the River Huebra, Duero basin are analysed. Females dominated older age classes and lived up to 6 years (5+) while males only reached 5 years (4+). The growing season extended from April to September; growth rates were similar for both sexes. 0+ fish condition increased during their first summer and spring. In older fish, condition cycle was related to gonad development and showed some differences between sexes. The number of females reaching maturity at age 1 + almost doubled that of males; females also matured at smaller size. Both fecundity and egg size increased with female length: mean egg counts varied between 974 for 1 + individuals and an estimated 10491 for 5+ fish. Eggs were produced as a single batch, but were released fractionally during April and May.     

Estimation of migratory history in female masu salmon Oncorhynchus masou (Brevoort, 1856) with the growth hormone pseudogene

To estimate the migration timing, length, and location of females with the growth hormone pseudogene (GHp), trace element analyses were performed on the otoliths of 40 wild adult masu salmon, Oncorhynchus masou (12 males, 19 normal females, and nine females with GHp [all fish were 3‐ or 4‐years‐old]) caught during the reproductive season (September) from 2004 to 2010 in the Atsuta River in Japan. Sr concentrations at the end of the otolith translucent area formed during the winter suddenly increased in all individuals, suggesting that they had migrated in the spring. In addition, the estimated migration length and location of females with GHp indicated that they had spent a fixed period of 1 year in the ocean, suggesting that females with GHp have a similar migratory history as that of normal females.     

黄海中南部细纹狮子鱼的生物学特征及资源分布的季节变化

根据2009年7—8月、10月和2010年1月、5月黄海中南部渔业生物底拖网调查数据,对该海域细纹狮子鱼的生物学特征及其分布的季节变化作了分析。结果表明,细纹狮子鱼平均体长和平均体重从春季(4.7 cm、3.3 g)到冬季(34.2 cm、764.9 g)呈显著增加,并且雄性个体平均体长显著大于雌性个体(P<0.05,春季除外)。性比(♀∶♂)随体长组和季节变化,体长越大趋向于雄性,反之趋向于雌性;夏季雄鱼居多(0.70∶1,P<0.05),秋季则为雌鱼居多(1.35∶1,P<0.05),而冬季(产卵群体)和春季性比接近于1∶1。细纹狮子鱼各季节摄食等级均在2.5以上,冬季雄性个体摄食等级显著大于雌性个体(P<0.05),但雄性个体肥满度为全年最低(1.52)。细纹狮子鱼相对资源量和贡献率从春季(0.17 kg/h,1.54%)到秋季(15.36 kg/h,33.05%)呈上升状态,而冬季(2.37 kg/h,5.60%)有所下降。相比2000年,夏秋季相对渔获量和贡献率提高明显。全年集中分布于7.8—13.6℃,3.20%—3.38%的水域,平均体重和水深有显著的相关性(秋季除外)。另外,根据性成熟个体分布区和稚幼鱼分布的相关历史资料分析发现,除海州湾外,黄海中部深水区可能是细纹狮子鱼的产卵场。     

Secondary production of Chasmagnathus granulatus (Crustacea; Decapoda) in a Ramsar Site from Argentina.

Secondary production of Chasmagnathus granulatus was calculated at the Refugio de Vida Silvestre Bahía Samborombón, Argentina (36 degrees 16' S and 57 degrees 06' W). Sampling was conducted on nine occasions between March 2001 and February 2003, crabs were collected by hand, physico-chemical variables, granulometry and organic matter contents of the sediments were registered. Crabs were classified as male, female and undifferentiated, measured (total carapace width: CW) and weighed (wet and dry weight: DW at 60 degrees C, during 48 hours). A correlation analysis between CW and DW was made. Morphometric growth of C. granulatus was by the application of the power function (y = a x (b)), where the carapace width (CW) was used as an independent variable. Males, females and undifferentiated individuals were analysed separately as well as all together as a group. The data were fitted indicating a positive allometry (constant of allometry b > 3), the males showing the greatest allometric value. The individuals (n = 957 juveniles and adults) were separated in cohorts by the polymodal width-frequency distribution converted into normal curves. Three cohorts were found during the whole study period, and two cohorts coexisting in each sampling date. Ovigerous females were caught on December 2001, 2002 and February 2003. The size-frequency method was used to estimate the annual production. The major contribution to production was carried out by the mature individuals, in particular those with size between 25 and 30 mm, but on the other hand, only few individuals measuring from 10 to 20 mm were collected. The annual production of C. granulatus was estimated in 7.76 g.m(-2). The biomass (expressed as total dry weight) varied between 0.55 and 1.85 g.m(-2), with the greater values being registered during autumn and spring, and the lower values during summer.     

An investigation of the advantages of autumn and spring stocking with brown trout Salmo trutta L. in a Yorkshire reservoir

Batches of trout have been introduced into Chelker Reservoir in Yorkshire in the autumn and spring since the 1870's for angling purposes. Six batches of tagged, hatchery-reared brown trout Salmo trutta L. were introduced from autumn 1966 to spring 1969. During the angling season fish introduced in the spring give better catches than those stocked in the autumn. At the beginning of the season the larger fish in the spring batch are caught more often than the smaller fish from the same batch. The larger fish in the autumn batch are caught more often than the smaller fish from that batch throughout the season. The population, available to the angler from the shore was estimated to be 1491 in 1968, with 722 fish/km of shoreline. More fish survive to a second year in the reservoir than is apparent from the number of tags returned. Fish introduced in the spring usually begin growing before those introduced in the autumn, thereafter growth rates varied. The growth rate was independent of the number offish stocked up to the numbers put in.
Batches of tagged trout were retained at the hatchery up to nine months to gain relevant experience of post-tagging mortalities, tag loss rate and effect of tags on growth.     

Energetics of a population of the isopod Asellus aquaticus: Life history and production

SUMMARY. A population of Asellus aquaticus in Wistow Lake, England, was sampled at monthly intervals from September 1973 to September 1974. The mean population density was 586 m⁻² in autumn 1973 but it fell to 67 m⁻² by autumn 1974. Evidence suggests that the lower density in autumn 1974 was due to premature mortality of gravid females. The cause of this is not known.
Gravid females were present from February to June and July to September, giving rise to spring and autumn cohorts. The larger members of the spring cohort reproduced in the autumn, the remainder in the following spring. The autumn cohort reproduced mainly in the following spring but later than the spring cohort. The bimodal length-frequency curves were analysed to separate the two cohorts and to estimate growth and production of each cohort separately. The overwintering spring cohort had a faster relative growth rate than the smaller individuals of the autumn cohort. Thus the spring cohort showed a P/B ratio of 2.62 for the period September–April compared with a ratio of 1.81 for the autumn cohort. The highest ratio of 6.42 was shown by the spring cohort in the summer (May–September).
Annual population production (P) was 3004.9 mg dry wt m⁻² from a mean biomass (B) of 757.2 mg dry wt m⁻². The P/B ratio of 3.96 is double the value reported for A. aquaticus in Sweden.     

Variation in the diet of the viperine snake Natvix mama in relation to prey availability

The diet of the viperine snake was compared with food availability in the Ebro Delta, a wetland largely occupied by rice fields, in 1990 and 1991. Snake selection of prey type and size was studied seasonally and by snake group: males, females and immature snakes. Overall, feeding activity (percentage of individuals with prey and number of prey per stomach) increased with food availability. Diet analysis showed that viperine snakes mainly foraged on the green frog Rana perezi (adults and tadpoles) and the carp Cyprinus earpio. Conversely, viperine snakes rejected the mosquito fish Gambusia holbroki which is the most abundant species in autumn, when Natrix maura has a low feeding activity. Statistical comparisons between viperine snake diet and prey availability showed that males selected small carp, immature snakes selected tadpoles and, in spring, females selected frogs. The selection of small carp by males may reflect a sexual divergence of trophic niche related to sexual size dimorphism, as females are larger than males. As tadpoles are presumably easier to catch than fish, tadpole selection by immature individuals may reflect variance in capture abilities. In spring, the selection of frogs by females overlapped with vitellogenesis, suggesting that females compensate for the cost of reproduction by selecting green frogs, which have a greater biomass and higher energy content than fish. Carps eaten in spring were smaller than in summer. Moreover, in summer viperine snakes selected smaller carp than the available mean size. This divergent tendency between carp size selection and carp size availability reveals how seasonal diet shifts in prey size selection may be a response to an increase in prey size.     

Some aspects of the biology and ecology ofKnipowitschia caucasica (Teleostei: Gobiidae) in the Evros Delta (North Aegean Sea)

Some aspects of the biology and ecology of the gobyKnipowitschia caucasica were studied over a period of 13 months in a poly-to euhaline area in the Evros Delta (North Aegean Sea). This fish grows rapidly in the summer and autumn after hatching, matures after its first winter, breeds from the end of April to the end of July, and grows rapidly again in July–September. The older males perish after their second February, whereas some females have a second breeding season at the end of April/beginning of May, shortly before their death. The fish grows to about 40 mm in total length. There is a positive correlation between the total length (TL) and the standard length (SL) or the cleaned body weight (CW). SL increases slower than TL, whereas CW increases slower than TL in immature individuals and faster in males and females. There is no difference between immature individuals, males and females, in the growth rate of SL, TL and CW, TL. The mean monthly values of the condition factor varies from 0.289 to 0.576 in females and from 0.313 to 0.548 in males. The overall sex ratio of females to males is 1: 1.46. Fecundity ranges from 60 to 217 eggs with a mean value of 109.8 and depends upon size, whereas relative fecundity varies between 968 and 2170 with a mean of 1558. The fish feeds predominantly on benthic amphipods and polychaetes.     

Mercury content in muscles of fish of the Selenga River and lakes of its basin (Russia)

Differences between the muscle mercury contents in fish from lakes Gusinoye and Karasinoye and the Selenga River may indicate an inconsiderable income of mercury in aquatic ecosystems with atmospheric precipitation, along with a more intensive migration of mercury with the riverine flux. The minimal concentration of mercury (less than 0.15 mg/kg, dry weight) has been registered in the muscles of Amur sleeper from Lake Karasinoye and of Baikal omul from Lake Baikal, while the maximal concentration (1.0–2.3 mg/kg, dry weight) has been revealed in the fish caught in the Selenga River delta (in predatory pike, Amur catfish, and perch, as well as in omnivorous roach and ide). The muscle metal content in dace decreased along the downstream direction.     

Effects of age and body size on gonadal development of Atlantic sturgeon

Three hundred and five Atlantic sturgeon caught in the Hudson River and Hudson Bight were examined for age, body size and gonadal development (histology). Sampled fish ranged in age from 1·5 to 43 years and fork length (LF) 48–244 cm, and included 144 females and 161 males. All young sturgeon (age 1·5–4 years) caught in the river had sexually differentiated gonads. Age and size distributions of subadults and adults at different stages of gametogenesis were sex-specific and conformed with von Bertalanffy growth curves. Males mature faster and at a younger age compared to the females. Females with mid-vitellogenic ovaries were not found and their absence may be related to fishing gear selectivity or out-migration into the ocean during ovarian recrudescence. Mature males and females caught during the spring spawning migration into the Hudson River, ranged in age from 12 to 19 and from 14 to 43 years, and LF 117–185 and 173–244 cm, respectively. Individual fecundity and diameter of fully grown ovarian follicles increased with age and body size, but this increase was dampened in older females. Three hermaphroditic fish were found and all exhibited sparse pre-vitellogenic ovarian follicles embedded in normally developing testicular tissue.