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.     

Annual growth rings, rainfall-dependent growth and long-term growth patterns of tropical trees from the Caparo Forest Reserve in Venezuela

1 Tree-ring analyses and dendrometer measurements were carried out on 37 tree species in a semi-deciduous forest of the Reserva Forestal de Caparo, Venezuela, where the mean annual rainfall is about 1700 mm and there is a dry season from December to March. The main purposes of the investigation were to show the seasonality of cambial growth, and the connection between precipitation patterns and tree-ring curves. Long-term rates of wood increment were also estimated.
2 Cambial markings in consecutive years showed that annual rings were formed by many species.
3 The distinctiveness of growth zones was usually greater in deciduous species than in evergreen species, although not all deciduous species had distinct rings.
4 Dendrometer measurements showed that the annual growth rhythm was related to precipitation patterns. Evergreen species tended to show only a short interruption of wood growth (during the later part of the dry season), whereas deciduous species stopped growth completely at the end of the rainy season.
5 For deciduous species, regression analyses showed close relations between tree-ring width and the sum of precipitation outside the rainy seasons (i.e. November to April). Evergreen species reacted to the total annual amount of precipitation.
6 Variation in longest available ring chronology (for Terminalia guianensis ) showed little correlation with the El Niño–Southern Oscillation effect.
7 On average trees from natural forests showed relatively constant growth over the entire life span. Plantation trees grew fast up to an age of 15–20 years, but annual increments then decreased to values seen in natural forest trees.     

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.     

The record of daily growth in otoliths of Atlantic silversides, Menidia menidia, from field and laboratory

Otoliths were removed from field-collected silversides of age less than 3 months. Otolith diameter was highly correlated with total length of the fish. Daily growth ring counts for this species are known to be a function of age rather than size, so widths for the daily growth rings provide a record of daily increases in length of the fish. Measurement of ring widths showed that weekly specific growth rate was greater than 70% at age 1 week, but declined to about 30% at age 1 month and about 15% at age 2 months. A laboratory experiment in which temperature was changed on a weekly basis demonstrated that environmental variables can affect the width of rings. Nevertheless, the growth rate of field-collected fish, as calculated from otolith ring widths, was more highly correlated with size of fish, as measured by otolith radius, than with the environmental variables of temperature, salinity and plankton abundance. Back-calculation of growth rates from otolith ring widths of five fish collected at the end of the growing season yielded the same age-growth curves as were obtained from 203 fish collected biweekly during the season.     

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.     

Seasonal and individual variation in gregarine parasite levels in the field crickets Gryllus veletis and G.pennsylvanicus

ABSTRACT. 1. Gregarines, debilitating protozoan gut parasites, were monitored in two species of field cricket, Gryllus veletis (Alexander and Bigelow) and G.pennsylvanicus Burmeister, in northern Michigan in 1983 and 1984.
2. Gregarines were found in 31–51% of G.veletis individuals and 50–70% of G.pennsylvanicus.
3. Males were more heavily infected than females in G. veleris , but G.pennsylvanicus males and females had nearly equal infection levels; this disparity resulted in an overall lower infection rate for G. veletis.
4. Both species had fewer gregarines in 1983 than in 1984, possibly due to the adverse effect of drier conditions in 1983 on development of parasite cysts in the soil.
5. Levels of infection were not constant throughout the breeding season for either cricket species.
6. Body size was not correlated with parasite load in either G. veletis or G.pennsylvanicus.
7. Adult age was unrelated to gregarine level in G. veferis , whereas G.pennsylvanicus showed a positive correlation between adult age and parasite load during two non-consecutive weeks of the breeding season.     

Maturity Ogives for South Pacific Albacore Tuna (Thunnus alalunga) That Account for Spatial and Seasonal Variation in the Distributions of Mature and Immature Fish

Length and age at maturity are important life history parameters for estimating spawning stock biomass and reproductive potential of fish stocks. Bias in estimates of size and age at maturity can arise when disparate distributions of mature and immature fish within a population are not accounted for in the analysis. Here we investigate the spatial and temporal variability in observed size and age at maturity of female albacore tuna, Thunnus alalunga, using samples collected across the South Pacific. Maturity status was identified using consistent histological criteria that were precise enough to allow for mature but regenerating females to be distinguished from immature females during the non-spawning season, permitting year-round sampling for maturity estimation in albacore. Using generalised linear mixed models, we found that the proportion of mature females at length varied significantly with latitude and time of year. Specifically, females at northern latitudes (∼10–20°S, where spawning occurs) were mature at significantly smaller lengths and ages than females at southern latitudes (∼20–40°S), particularly during the spawning season (October–March). This variation was due to different geographic distributions of mature and immature fish during the year. We present a method for estimating an unbiased maturity ogive that takes into account the latitudinal variation in proportion mature at length during a given season (spawning or non-spawning). Applying this method to albacore samples from the western region of the South Pacific gave a predicted length at 50% mature of ∼87 cm fork length (4.5 years).     

Juvenile migration in brown trout: a consequence of energetic state

1. We explored the mechanisms determining age and size at juvenile migration in brown trout Salmo trutta L. A ¹³³Cs tracer methodology was used to estimate food consumption of juvenile brown trout in a Norwegian stream, and the energy budgets of early migrants and stream residents were compared.
2. Fast-growing brown trout migrated to the lake earlier and at a smaller body size than slower-growing individuals. The 2+ migrants were significantly larger than those that remained 1 or more years longer in the stream. The 3+ migrants were significantly larger than the 2+ migrants. Some fast-growing males matured in the stream, whereas all females left the stream before maturing sexually.
3. The food consumption and the energy budgets for 2+ migrants were more than four times higher than those of the resident 2+ fish. Total energy allocated to growth was also higher among migrants, and the total metabolic costs were five times higher among migrants than among resident fish.
4. The proportional energy allocation to growth among the 2+ migrants was much lower (about half) than that of those remaining longer in the stream. The reduction in the proportion of energy available for growth from age 1+ to 2+ was larger among migrants (88%) than among resident fish (68%). Reduction in the proportion of energy available for growth is a probable explanation for why migrations are initiated at age 2.
5. Our study supports the hypothesis that fast-growing individuals shift their niche earlier and at a smaller body size than slower-growing individuals because they maintain higher metabolic rates and are energetically constrained at a younger age by limited food resources than slow growers.     

Phenotypic variability in nesting success among Osmia lignaria propinqua females in a glasshouse environment: (Hymenoptera: Megachilidae)

Abstract. 1. The phenotypic variability of several estimates of fitness among seventeen nesting female O.lignaria Cresson was examined in a glasshouse provided with abundant resources.
2. Females exhibited wide variation in: (a) number of nests and cells made and in their rate of construction, (b) the incidence of mortality of offspring, and (c) the percentage of male offspring produced (52–100%).
3. In confirmation of earlier field studies: (a) more offspring of both sexes were produced during the first half of the nesting season, (b) most female offspring were produced early in the nesting season, (c) most parental investment during the last half of the flight season was made in male offspring, (d) there was a decrease in offspring size with season, with females decreasing more than males, and (e) the ratio of female/male body weight was = 1.8. These results appear to be due to ageing rather than to a reduction in resource availability.
4. No relation between female size and fecundity was evident.
5. There was no evidence that small females tended to produce a greater proportion of the smaller sex (males) than did large females.
6. Smaller offspring of both sexes had a much greater probability of dying overwinter than did large offspring. However, where the sexes overlapped in size (large males, small females), almost all females died and almost all males survived. We hypothesize that as size of offspring produced declines with season, a greater proportion of males are produced because they have a much greater probability of surviving at small body sizes.     

Age, growth and reproduction of Aphanius iberus (Cuv. & Val., 1846) in the lower reaches of the Guadalquivir river (south-west Spain)

SUMMARY. 1. Age, growth and reproduction in an Atlantic population of the small fish, Aphanius iberus (Cuv. & Val., 1846), from the estuary of the Guadalquivir river were studied.
2. The growth period was from April to September and the annulus on the scales was formed in April.
3. The life-span was short with a winter age-structure of 95.9% 0+ fish, 3.9% 1+ and 0.2% 2+.
4. The fecundity of this stock, before the beginning of reproduction, is represented by the formula: Fec=0.907 TL (cm)^4.099. During the reproductive period 1+ females contained more, smaller eggs g⁻¹ of gonad than 0+ fish.
5. Males matured before females, but females were larger than males. The overall sex ratio did not differ from 1:1 but males dominated significantly during most of the spawning period.
6. Aphanius iberus spawned intermittently during the reproductive period. From April to July, 1+ group specimens (7–12 months old) reproduced. Their offspring (0+ group; 3–4 months old) reproduced from July to September. Very few of the 1+ group specimens survived to spawn the following year.
7. Mean gonadosomatic indices were much higher in the 1+ group than in the 0+ group and in females compared to males.
8. The loss of condition and the disappearance of the 1 + group during spawning, may indicate the cost of a prolonged high level of reproductive effort.
9. In this productive environment, the life history of Aphanius iberus is similar to that of Gambusia affinis (Baird & Girard, 1853) and Fundulus heteroclitus (Linnaeus) found in the same area.     

湘华鲮的生物学研究

湘华鲮是湖南沅江中上游的一种主要经济鱼类。主要以硅藻为食。1+龄鱼的平均体长为22厘米,平均体重为273.7克;2+龄鱼的平均体长31.3厘米,平均体重704克;3+龄鱼的平均体长为39.2厘米,平均体重1479克。渔获物中的年龄组成,以2+、3+、4+龄为主,渔获物中最大年龄和最大体重为6+龄、3400克。江河生长的湘华鲮,雌性性成熟年龄多为3年,雄性提早成熟一年;达性成熟年龄的雌性以Ⅳ期卵巢越冬;达性成熟年龄的雄性精巢,在冬季发育至Ⅴ期;它的生殖季节为4月底至5月下旬。在江河中有自然产卵场;4—5龄的雌性湘华鲮,成熟卵巢系数为8—17.6%,卵径约2.0—2.2毫米,每克卵粒数为293—321。       

Age, growth and reproductive parameters of the Mediterranean cardinal fish, Apogon imberbis

Life history parameters (age, growth and reproductive characteristics) of the Mediterranean paternal mouthbrooding cardinal fish, Apogon imberbis, were investigated at a coastal locality off Blanes, NW Mediterranean Sea. Maximum age was found to be 5 years for both sexes. Age was validated with an otolith chemical (tetracycline) marking experiment. Both females and males reached maturity at length >5.5 cm, corresponding to 1 year of age in both sexes. The spawning season ranges from July to October, with a peak in August. The number of eggs in the mouths of males increased linearly with fish total length.     

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.     

Production biology of the upland bully Philypnodon breviceps Stokell in a small New Zealand lake

The life history, food habits, feeding and locomotory activity rhythms of the upland bully, Philypnodonbreviceps Stokell were investigated (February 1969-March 1970) as a basis for studying the relationships between food consumption, biomass and production of the species in a small, moderately eutrophic lake (one of a pair of adjacent lakes at an altitude of 610m in the South Island, New Zealand, known collectively as Spectacles Lakes). Annuli formed on the scales during August and September and could be used as valid indicators of age, although small fish could be aged simply by length frequency analysis. The maximum life-span for both sexes was observed to be 4.5 years but growth of males considerably exceeded that of females. Because females matured at a smaller size than males, mature females were in excess of mature males (3.7: 1). Each female laid only one batch of eggs during a short breeding season in spring (October-December) but several females contributed eggs to each nest. Fecundity ranged from 60–440 eggs per female; the relationship between egg number ( F ) and length ( l ) was log F =–1.609+2.314 log l and between egg number and age ( A )was F =–93.51+109.93 A. Larvae hatched in approximately one month (water temperature 14.4-17.5°C) and the yolk sac became absorbed after a further eight days. Some fry remained pelagic for up to six months. Fry fed predominantly on Crustacea, but the diet changed to larger insect larvae and young of its own species with increasing age and size of the fish. The diet also varied, but to a lesser extent, with season and the time of day. All age groups showed diel rhythms of feeding and locomotory activity which, however, exhibited complex seasonal phase shifts throughout the year. In general, periods of higher feeding intensity appeared to follow closely the periods of increased locomotory activity. The activity level of larger fish was higher than that of smaller fish.     

A preliminary study of the age and growth of the Cyprinid fish Barilius moorii Blgr. from Lake Kivu

The age and growth of the Cyprinid fish Barilius moorii from Lake Kivu is studied by means of the growth rings occurring in the scales. Although the moment of ring formation and the duration of one growth season were not known, both overall length growth in a population as well as individual length growth could be calculated. Increase of weight was obtained from length growth on the basis of a length-weight relationship. By comparing the growth parameters of the von Bertallanfy equation and data from the literature, a hypothesis is formulated that ring formation should occur at the transition from a dry to a rainy season, and that two rings a year should be formed. Ring formation on the scales might be due to gonad maturation, but this could not be demonstrated.     

The nesting biology and population dynamics of the Seychelles potter wasp Eumenes alluaudi Perez

Abstract. 1. The nesting biology of the solitary potter wasp Eumenes alluaudi was studied on Cousin Island, Seychelles.
2. Although the rainy season was from October to April there was no indication of strong seasonality in the wasps' nesting.
3. Females tended to nest close to where other females were nesting.
4. The mean number of cells per nest was 3.71, the mean number of nests made per female 135, and the percentage of cells from which adults emerged 65.87; thus the mean number of adult wasps emerging from the nest(s) of each breeding female was 3.29.
5. Male-producing eggs were laid before female-producing eggs and the estimated sex ratio at emergence was, at 1:2.52, female biassed. It is possible that inbreeding occurred.
6. Daily mortality of nesting females was estimated as 0.088.
7. The mean interval between a female's emergence and her starting to nest was 19.7 days.
8. Marking showed that only 26.7 ± 6.3% of females emerging from cells in the study area returned to breed there. Since the number of emerging daughters per breeding female was only 5.01 times 0.66 times 0.72 = 2.36 (fecundity x proportion emerging x proportion of females emerging), the number of returning females would be only 236 times 0.267 = 0.63, and hence, in order to maintain numbers over many generations, 037 females must have been immigrants.     

Age and size-dependent variation in the seasonal timing and probability of reproduction among mature female pumpkinseed,Lepomis gibbosus

Synopsis In this study, we used pumpkinseed,Lepomis gibbosus, populations in two east-central Ontario lakes to test for age and size-dependent effects on the probability and timing of reproduction of mature females. Pumpkinseed body size characteristics differed in the two lakes; Little Round Lake harbours a stunted population and Beloporine Lake does not. Age-class distribution of mature females was determined by a maturity assessment on fish collected just prior to spawning and at the mid-spawning period, combined with an early-season capture-mark-recapture survey. Spawning females were collected throughout the breeding season to assess age and size-related temporal trends, and to compare their age and size distribution with that of mature females at large. The proportion of age 2 females in Little Round Lake that actually spawned was considerably lower than the proportion of mature age 2 females at large. Furthermore, age 2 females that spawned in this lake did not do so until late in the breeding season. In contrast, the proportion of young/small females spawning in Beloporine Lake was comparable to the proportion of young/small mature females at large, and both small and large females spawned throughout the breeding season. Small mature females in Little Round Lake may have had no other option but to spawn late in the season because of their poor body condition. In Beloporine Lake, condition factor early in the breeding season in age 2–4 females was higher than that of Little Round Lake females, suggesting that limited energy reserves in the spring may have prevented young Little Round Lake females from early spawning. Our results show that the likelihood and timing of reproduction are both age and size-dependent in some populations. Small individuals that delay seasonal maturation and spawn late in the summer probably contribute little to the population due to the restricted growth and reduced overwinter survival of their progeny.To whom correspondence should be addressed     

Seasonal emergence, host-seeking activity, age composition and reproductive biology of the mosquito Aedes punctor

Abstract. 1. Seasonal patterns of adult emergence, host-seeking and reproductive ageing in a population of the woodland mosquito Aedes punctor (Kirby) are described from field studies in northern Britain in 1984 and 1985.
2. The pattern of emergence showed little variation between years but duration did vary. Males started emerging before females. Sex ratios at emergence showed a marked female bias. A late, second period of emergence apparently represented a second generation in this normally univoltine species.
3. Host-seeking females were first caught at human bait within a few days of the start of emergence and peak numbers at bait occurred 3–4 weeks later. High numbers lasted for c. 2 weeks. The duration of host-seeking activity was related to weather. The second emergence in 1985 resulted in a second peak of activity in early September and probably extended the flight season.
4. As the season progressed the proportion of females that were parous increased. However, this proportion never reached 1.0, indicating variation in individual reproductive success, which differed between years.
5. The reproductive biology of individuals within the population was investigated. No autogeny was detected, suggesting that the population was entirely anautogenous.     

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     

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

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