Observations on the age, growth, reproduction and food of the roach Rutilus rutilus (L.) in two rivers in southern England

Scales and opercular bones from 632 roach from the River Stour were used for age and back-calculated growth determinations. The scales had clearer inner annuli but operculars clearer outer annuli in fish more than nine years old. The annuli were laid in late May or early June at the beginning of the growth period. Growth was minimal between November and April. Roach from both rivers grow faster than those in most other European waters. Female roach grow faster than males; River Frome roach faster than those from the Stour. Spawning occurred in May and elaboration of gonads between September and May. Immature roach have an annual cycle in condition with a maximum in June and a minimum in early Spring. The condition of mature females is affected by the gonad cycle. The fecundity of Stour roach is represented by the formula: log egg number=4.43 log length (mm)—1.69. Approximately half of the Stour males attained sexual maturity at age III and most of the rest by age IV. Half of the females were mature at age IV and the remainder by age V. Both brood success and growth rate varied from year to year but independently of one another. Most Stour roach ate aquatic insect larvae and molluscs but algae were more frequent in the diet of larger fish.     

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.     

Observations on the age, growth, reproduction and food of the dace, Leuciscus leuciscus (L.), in two rivers in southern England

Scales of 497 dace from the river Stour and 573 from the river Frome were used for age determinations. Annuli were laid down in late May to early June at the start of the growth period. Minimal growth occurred from November to April. Male dace grew minimally faster than females; Frome dace faster than those from the Stour. Growth rates in the two rivers were similar to those published for most other European waters. Variation in growth rates in different years was not great, but there were marked differences in recruitment success. Spawning occurred in the second half of March and elaboration of the gonads between September and March. Immature dace have an annual cycle in condition with a maximum in June and a minimum during the winter months. The condition of the mature females is affected by the gonad cycle. The fecundity of Stour dace is represented by the formula:

and for Frome dace by:

Most dace were mature by age IV, but there were more mature II and III group fish in the Frome population. Molluscs and Trichoptera larvae comprised the bulk of the winter diet of Stour dace, and Ephemeroptera nymphs, Simulium and chironomid larvae were the principal constituents during the summer.     

Observations on the age, growth, reproduction and food of the pike Esox lucius (L.) in two rivers in southern England

Opercular bones of 261 pike from the River Stour and 117 from the River Frome were used for age and back-calculated growth determinations. The annuli were laid down during late April and early May and most growth occurred between May and September. Pike growth in the two rivers was comparable with the fastest growth in other waters, though Frome pike grew slightly faster than Stour pike. Spawning occurred from the end of March into May. Elaboration of the ovaries commenced in September and was virtually completed by February, whereas the testes reached their maximum weight in October and maintained it until spawning. Immature pike had an annual cycle of condition reaching a maximum in May and a minimum during the winter. The gonad cycle affected the condition of mature females which had their minimum condition in mid-summer. The fecundity of Stour pike is expressed by the formula: log₁₀ egg number =3.56 log₁₀ fish length (mm) – 5.40. Approximately 75% of all Stour pike were sexually mature by age II and these fish were, on average, larger than immature pike of the same age. The most numerous items in the diet of pike were small cyprinids, 30–80 mm fork length, although pike over 700 mm long ate larger fish. Few salmonids appeared in the diet of either Frome or Stour pike. The percentage of empty stomachs was highest in Stour samples taken during the summer, shorter digestion times and longer feeding periods in this period are suggested as reasons for the apparent anomaly.     

The autecology of the chub, Squalius cephalus (L.), of the River Lugg and the Afon Llynfi

(1) Analysis of data from samples of chub taken at monthly intervals from two tributaries of the Herefordshire Wye revealed an annual cycle of scale growth with the formation ofa check during May or June. The frequency distributions of ages deter-mined from scale checks and the length-frequency distributions showed close simi-larities. It was concluded that age determinations based on an examination of the scales were valid, provided care was taken in the identification ofthe first scale cheek. The maximum age observed was 15 years. (2) Examination ofthe population structure revealed an overall sex ratio close to unity but there was a significant increase in the proportion of females in the 11 + and older age groups. Dominant year-classes were observed. The strongest was 1959, which was attributed to exceptionally warm, dry, sunny weather during the period May-September. (3) Female chub grew more rapidly and attained greater ultimate size than the males. Changes in the pattern of growth during the life-span were attributed to the attainment of sexual maturity, especially in the females. The length-weight relation-ships of the sexes diflFered slightly but were almost identical for the same sex in the two rivers studied. Seasonal variations in the growth-rate were followed. Most rapid growth occurred after check formation in May or June and continued until September.     

The autecology of the chub, Squalius cephalus (L.), of the River Lugg and the Afon Llynfi

(1) The pattern of absolute atid relative gonad growth during the life-span and the seasonal gotiad cycle were determined from monthly samples of chub taken from two tributaries of the Herefordshire Wye. (2) A marked change in the pattern of absolute gonad growth was thought to indicate the attainment of sexual maturity. This was found to occur synchronously with corresponding changes in the pattern of body growth described previously and was in agreement with the age at which a seasonal gonad cycle was detectable. (3) Sexual maturity was attained during the eighth year of life (7+) in female chub and in males from the Afon Llynfi, but most males from the River Lugg matured a year earlier. (4) The chub gonads continued to increase in relative size after the attainment of sexual maturity. This was more evident in female chub. (5) Seasonal changes in the gonad condition and weight were followed. Gonad maturation occurred during spring and the gonad mass increased rapidly just prior to spawning. (6) Spawning occurred during June.     

Growth of dark chub, Zacco temmincki (Cyprinidae), with a discussion of sexual size differences

I examined the annual and seasonal growth of dark chub, Zacco temmincki, in a Japanese river. Investigation of opercular rings showed that the fish reached a maximum age of 8 years. There was no significant sexual size difference at younger ages (3–5 years), but males were larger than females at older ages (6–7 years). Annual increments of length and weight for males that were recaptured were also larger than those for females. The fish spawn from June to August. Females grew for a short period from April to May, but males on average grew for a longer period from April to August. There was no sexual difference in growth rate except during the spawning period. Annual growth rate was negatively correlated with fish length in each sex. The sexual size differences at older ages of the fish might be due to the polygynous mating system in which most mature males could not obtain females and invested for somatic growth in the spawning period, and a short growing season that was overlapped considerably with the spawning period.     

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.     

The growth, reproduction and food of the roach Rutilus rutilus (L.), of the River Lugg, Herefordshire

Checks were formed on the scales in June and July. A dominant 1959 year class accounted for half the population present in 1964. Females grew faster than males and attained greater ultimate size. Growth in the River Lugg was good in comparison with rates in other British waters. The sex ratio was found to change with age; a predominance of males in the youngest age classes changed to a preponderance of females in the older classes. The youngest fishes caught (3+) were already sexually mature. The gonads were found to be a constant proportion of the body weight for fishes of all sizes at a given season. Spawning was completed by June; males were ripe in May. The ovaries recovered more rapidly than the testes after spawning. Seasonal variation in feeding activity, with higher activity in summer, was observed and could be correlated with temperature. Seasonal changes in the diet could be related to availability. The diet was predominantly vegetable; the most important animal component, aquatic insect larvae, accounted for 11 % of the total diet. Aerial insects were rarely eaten. Diet varied with age: molluscs being particularly important to older roach; younger roach consumed large amounts of substrate material. There is some evidence that young roach indiscriminately ingest substrate material but older roach are more selective and reject inert material.     

Distribution, movements, and mortality of anadromous arctic char, Salvelinus alpinus L., in the Cumberland Sound area of Baffin Island

During 1972 the downstream movement of anadromous artic char, Salvelinus alpinus L., from two rivers flowing into Cumberland Sound, Baffin Island, began during the middle of May and was completed within 2 weeks. This movement took place during both the day and night. Upon reaching saltwater, many char older than 9 years (longer than 20 cm) began to migrate along the shore of the Sound at a rate of 0–6–0-9 km/day with the result that the average maximum distance travelled from the natal river was 40–50 km. Char 6–9 years old, 10–20 cm in length, remained much closer to the rivers while those younger than 5 years never entered saltwater. During the period of saltwater residence, the fish frequently moved into the intertidal zone and freshwater. Maturing fish of both sexes were occasionally found in saltwater. The upstream migration to the lakes began during the second week of August and was completed within 5–6 weeks. Females tended to ascend the rivers before males, although fish of all different size and age migrated upstream simultaneously. Migration occurred during both the day and night. The maximum distance anadromous char moved from saltwater was 40 km. The char were found only in freshwater between May and September and were normally located near the bottom of lakes at a depth of 15–40 m. During this period, large scale movements were probably very limited. Average annual mortality was estimated at 16.0% per year with the highest rates (25–30%) occurring at ages 10 and 15–17 years. Many fish probably died of old age but physical deterioration during and after spawning was also an important cause of death.     

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.     

The growth and reproductive strategy of the gudgeon, Gobio gobio (L.), in two hard-water rivers in southern England

Scales from 682 gudgeon from the River Frome and 504 from the River Stour were used for age determinations. Growth in length was confined to the period May to October, but some weight increase occurred during the winter because of gonad development. Growth rates in the two rivers were the same, and were higher than most of those reported from other European rivers. Wide fluctuations, up to 12-fold, occurred in the year-class strengths of Frome gudgeon, caused by variations in the survival of juvenile gudgeon in their first year of life. Density-independent factors, particularly water temperature, were major influences. Female gudgeon grew marginally slower than the males, but they matured earlier and at a smaller size. They were fractional spawners but their total reproductive effort each season was high. Both sexes had low survival rates and their reproductive life spans were rarely more than three years. These life history traits support the premise that these gudgeon populations are r-selected.     

The role of life history in the relationship between population dynamics and environmental variability in two Mediterranean stream fishes

Chub Squalius torgalensis and nase Chondrostoma lusitanicum , in a Mediterranean stream, showed important differences in life-history traits and population dynamics. Both species reached mean maturity at age 2 years. Chub lived up to age 5 years, spawned in March to June, grew at a maximum rate of 0·59 mm mm⁻¹ year⁻¹ and showed a low reproductive allocation, with fecundity and egg size increasing with body size. Nase lived up to age 4 years, spawned in January to April, grew at a maximum rate of 0·46 mm mm⁻¹ year⁻¹ and showed a high reproductive allocation, with egg size independent of body size. Both chub and nase showed moderate fluctuations in population size during 1991–1998, but differed in factors driving density at age. Density of age 1 year juvenile chub decreased following severe summer droughts and proportionate survival prevailed thereafter. Density of age 2 year adult nase decreased following severe spring floods, but neither environmental nor parental stock effects were detected for juveniles and older fishes. The results illustrated the interplay between life history and environmental variability in driving fish population dynamics, with impacts of both summer droughts and spring floods being contingent on species-specific patterns of spawning and reproductive investment.     

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.     

Diet composition of chub,Squalius cephalus (Teleostei: Cyprinidae), in Lake Tödürge,Sivas, Turkey

Digestive tract contents of 241 specimens captured between March 1998 and November 1999 were analysed using both qualitative and quantitative methods to determine diet composition and feeding habits of Squalius cephalus (L., 1758) inhabiting Lake Tödürge, Turkey. Ages ranged from I to VI years; 60.6% of the fish were females, 39.4% males. The chub population appeared to consume a wide range of food items such as phytoplankton, zooplankton, nematodes, insects, fish, macrophytes, plant and animal detritus, whereby zooplankton (69.2%) predominated. Although individuals in the age I group preferred plankton (phytoplankton frequently; zooplankton infrequently), the older specimens (age groups IV, V and VI) behaved mostly as carnivores but also consumed some macrophytes. While there were no significant differences between diet compositions of males and females, seasonal changes were observed in frequency of occurrence, quality and quantity of consumption, and feeding activity. The chub specimens fed most heavily during spring (the pre‐spawning period: March, April and May). Highest food volume (13.0 cm³) consumed was in May and the lowest in September (2.0 cm³) while also being correlated with temperature. All of the food items were found in the digestive tract (82.1% of the specimens examined over all seasons). Highest fullness (84.9%) was reached in autumn and the lowest during summer (79.8%).     

Growth and life history traits of Aegean chub,Squalius fellowesii (Günther, 1868) in streams in Muğla Province,Aegean coast,Turkey

To aid in species' conservation, the aim of this study was to provide initial findings on age, growth and reproduction of an endemic species, Aegean chub Squalius fellowesii (Günther, 1868) populations from streams in the Aegean region of Mu?la Province, Turkey. The species is relatively short‐lived (maximum 6 years), attaining a size of about 200 mm total length with a rapid growth to first maturity (≈60 mm TL), and relatively little growth thereafter. The male:female ratio was 1.0 : 0.6, males significantly outnumbering females in the majority of the streams. General condition values of individual fish varied between 2.9 and 3.4. Sexual maturity was usually achieved later and at larger sizes in females than in males. Sexual maturation in most populations was at the age of 2 years in females and 1 year in males. The species spawns between early April and late May. Mean absolute and relative fecundity were about 4440 eggs and 57 eggs·g^?1, respectively. Mean egg diameter was 1.00 ± 0.03 mm, ranging from 0.70 to 1.20 mm. Suggestions for the conservation of Aegean chub are discussed.     

Life-history patterns of the mosquito-fish, Gambusia affinis, in the estuary of the Guadalquivir river of south-west Spain

SUMMARY. 1. The age, growth and reproduction of the small, introduced fish Gambusia affinis (Baird & Girard, 1853) were studied in the estuary of the Guadalquivir river.
2. The life-span was very short, the stock contained only two age groups: with annulus (1+ group; 10–12 months old) and without annulus (0+ group).
3. In both sexes growth restarted in April when the annulus appeared, but whilst 1+ males stopped growth, 1+ females grew steadily to June. Growth of 0+ spawners was only evident in September, the last month of the reproductive period. A differential growth rate between sexes was also evident.
4. 1+ specimens reproduced during May and June and their offspring from July to September. In both age groups somatic condition progressively declined during the spawning period.
5. The loss of condition and the disappearance of 1 + and the larger 04-specimens after reproduction may indicate the cost of a prolonged high level of reproductive effort.
6. The total fecundity (taken as the number of embryos) of 1 + females was represented by the formula: Fec=5.08 T.L. (mm) -170.07 and that of 0+ specimens by: Fec=2.23 T.L. (mm) -42.92. The maximum average monthly fecundity was reached in June when the length of the mother was at its greatest.
7. Length at first maturity was smaller in 0+ group than in the 1 + group; the difference between the two groups was greater in males (≅5 mm, T.L.) than in females (≅3 mm, T.L.). Also the average total length of 14-spawners was greater than 0+ spawners. There were significant differences in the overall sex ratio of 956 males to 2057 females.
8. The differences found in growth and reproduction between the two age groups suggest that life-history tactics may vary not only between different stocks but also within the same stock among its different components.     

The reproductive cycle of Coregonus lavaretus (L) in Loch Lomond, Scotland, inrelation to seasonal changes in plasma cortisol concentration

The reproductive cycle of Coregonus lavaretus (L.) in Loch Lomond, Scotland, was investigated by monthly sampling. Spawing takes place during the first 3 weeks of January, on offshore gravel banks. Males congregate on the spawning-grounds throughout the spawning period, while ripe females cruise in unisexual shoals in deeper water. Individual females migrate to the spawning-grounds as ovulation takes place, spawn, and return to deep water. After spawning, the gonadosomatic ratio and somatic condition factor of both sexes decrease until June or July. Gonad recrudescence occurs in males between July and October, and in females between July and December. The somatic condition factor of both sexes rises from its minimum in June or July to its maximum in September. A competitive protein binding assay was used to determine cortisol levels in 0–1 ml plasma samples of individual fish. The lowest cortisol levels occurred in fish caught by seine-netting and killed immediately by anaesthesia in MS 222 (Sandoz). Seine-netting and killing by concussion induced higher cortisol levels, in the range of 3–5 ng/100 ml. Cortisol levels in fish caught by gill-netting for 18 h were 3–6 times higher than in seine-netted fish, and the method of killing was immaterial in this case. The length of time spent in the gill-net had no significant effect on cortisol level, but maintenance of the fish in aquaria for 24–80 h elicited high cortisol levels of over 50 μg/100 ml. Post-mortem delay before blood-sampling resulted in lowered cortisol levels. Seasonal variations in cortisol level were determined in gill-netted fish throughout the year, and in seine-netted fish when available. Cortisol levels were high in both sexes in September; and very high in ovulating females caught on the spawning-grounds, though not in ovulating females caught off the spawning-grounds.     

Growth, body condition and demography of wild banteng (Bos javanicus) on Cobourg Peninsula, northern Australia

Growth, body condition and demography of a sample of 125 banteng, Bos javanicus , from a largely unharvested wild herd on Cobourg Peninsula in northern Australia were examined. Growth (measured as changes in age-specific head-length) was sexually dimorphic, males growing faster and attaining larger sizes than females. Females reached maximum size in three to four years, and males in five to six years. Body condition (measured by the kidney-fat index) was low amongst juveniles, increasing into middle age. Condition of aged females showed a marked decline. Males attained sexual maturity between three and four years, females between two and four years. Fecundity declined in older females. Breeding was seasonal, mating activity peaking during October and November, with births most frequent between June and August. Mortality amongst calves was high over the first six months of life, declining rapidly amongst older animals. Comparison of demographic data with those reported for captive herds indicates that the wild banteng in this study matured later, were less fecund, and suffered a higher rate of juvenile mortality. Lower fecundity and higher juvenile mortality were associated with patterns of age-specific body condition, suggesting that food availability was the major factor affecting demography and hence rates of change in banteng abundance.     

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.