Sex ratio, spawning season and size at maturity of red bandfish in the western Aegean Sea

The red bandfish Cepola rubescens is characterized by a normal gonochoristic sexual organization. The overall male: female ratio did not differ significantly ( x ²=4.57, P <0.05) from the theoretical 1: 1. However, the male: female ratio differed with season and length class and these differences are most probably related to sexual differences in growth rate, natural mortality rate and energetic cost of reproduction. Red bandfish spawns over an extended period, from late spring to mid autumn, with larger females spawning earlier than smaller ones. Males reach maturity at a larger total length, 299 mm, and age, 2.6 years, than females, 219 mm and 1.9 years respectively, a fact most probably indicating the existence of social structure in red bandfish. Finally, red bandfish matures at a comparatively smaller length and age than other fish species.     

Maturation, spawning and growth of rock soles off Kodiak Island in the Gulf of Alaska

Northern rock sole Lepidopsetta polyxystra females from the Kodiak Island area, Alaska, reached 50% maturity at 328 mm L _T and an average age of 7 years. In contrast, southern rock sole Lepidopsetta bilineata females reached 50% maturity at 347 mm L _T and an average age of 9 years. Spawning started in midwinter for northern rock sole and peaked during the spring, while spawning for southern rock sole occurred during the summer. The bottom depth for spawning northern rock sole ranged from 43 to 61 m and averaged 45 m; spawning depth for southern rock sole ranged from 35 to 120m and averaged 78m. Both species appeared to develop a single stock of oocytes and to ovulate them in a single spawning. Northern rock sole females grew faster overall ( K =0.24) than southern rock sole females ( K =0.12) but reached a smaller maximum length ( L _∞=430 mm) than southern rock sole ( L _∞=520mm). Males of both species grew more slowly than females after 5 years of age and reached a smaller maximum length.     

Age and growth parameters of Siganus sutor in Kenyan marine inshore water, derived from numbers of otolith microbands and fish lengths

Siganus sutor (Valenciennes, 1835) is, together with the Lethrinidae, commercially the most important fish of Kenyan waters. Age and growth parameters of this fish have been estimated for stock assessment purposes, using the von Bertalanffy growth model while taking into account the initial small but finite length of fish, L _o. Microbands on the otoliths were used as a measure of age in days. Data of fish length against numbers of microbands were fitted to the growth formula by a least squares procedure applied to a non-linear fit. This gave an L _∞ of 36.2 cm s.l. and a K of 0.87 on an annual basis. Independently, a curve was fitted by eye to the same data, and values were read off the curve and used in a standard Ford–Walford plot. This gave an L_x of 35 cm and a K of 0.9. The close agreement of the values obtained by the two methods, and of these with values in the literature, demonstrates the value of using microbands for determining growth parameters in a tropical fish.     

Population ecology of the paddy field-dwelling fish Channa gachua (Günther) (Perciformes, Channidae) in Sri Lanka

A population of Channa gachua in a small irrigation canal that supplies rice fields was studied by monthly sampling over 2 years. The population density was positively correlated with the rainfall and varied from 0.34 to 0.95 individuals m⁻². The growth parameters of the von Bertalanffy growth equation determined on monthly size–frequency data were L_x = 179 mm total length and K =0.50. Overall male to female ratio was 0.82 and there were more females than males in the middle size classes. Spawning occurred throughout the year, but all evidence indicated enhanced breeding during major rainy periods of May to July and October to December. The length at first spawning was 102 mm, which is reached in about 20 months. Fecundity, which varied between 389 and 2130, was positively correlated with gonad weight, body weight and total length. Longevity and natural mortality were estimated as 6 years and l.27 yr⁻¹, respectively. However, 99% of the population appeared to live for only 3 years. The mean biomass, average annual production and turnover ratio of the population were 7.35 g m⁻², 12.06 g m⁻² and 1.64, respectively.     

Aspects of the ecology of bream, Abramis brama (L.), in a gravel pit lake and the effects of reducing the population density

The growth of bream, Abrumis brumu (L.), in a gravel pit lake was considered to be good in 1982/1983 (L_x=663cm, K=0.105). Theadult breampopulationwasdominated by the 1973and 1976 year-classes. These year classes still formed most of the spawning population in 1987, but had grown very little (<2 cm) in the previous 5 years. In November 1987, 158 kg ha⁻¹ of bream were removed from this lake and in I988 the remaining bream population showed an increase in growth (mean length by 2.7 cm and mean weight by 0.5 kg) and condition (1.87 in 1987 to 2.09 in 1988) in one growing season. This additional growth of an ageing stunted bream population is considered to be the result of an increased food supply after reducing the fish density.     

Intraspecific Variations in Size- and Age-at-maturity for Red Bandfish, Cepola macrophthalma

Intraspecific variations in size- and age-at-maturity were studied in red bandfish, Cepola macrophthalma, in two adjacent gulfs of the western Aegean Sea, in the southern of which the population of red bandfish is stunted. Samples were collected with a commercial trawler over a grid of 34 stations at depths ranging from 22 to 222m. The hypothesis tested was that length and age at 50% maturity, Lm50 and tm50 respectively, for males and females do not differ in the two regions. The results showed that the Lm50 of both males and females in the northern area was by 3.5cm larger than that in the southern area and the 95% confidence intervals of Lm50 in the two areas did not overlap. Although the tm50 of males was larger in the northern area, the 95% confidence intervals of tm50 overlapped in the two areas whereas for females, the tm50 was larger by 0.4 years in the northern area and the 95% confidence intervals of tm50 in the two areas did not overlap. Stunting of the red bandfish growth in the southern area is the result of the combination of an extremely low food availability with higher temperatures prevailing in that area. Implications of these fine spatial scale intraspecific differences for the fisheries management of the highly oligotrophic eastern Mediterranean Sea are also discussed.     

Regional, interannual and size-related variation of age 0 year walleye pollock whole body energy content around the Pribilof Islands, Bering Sea

Mean whole energy content ( E _wb) of age 0 year walleye pollock Theragra chalcogramma was 19.928 KJ g⁻¹ dry mass in 3943 fish collected from different habitats around the Pribilof Islands frontal structure, south-east Bering Sea, during September 1994–1996 and 1999. It varied, however, with habitat type. Fish residing offshore had higher E _wb than fish residing inshore of the frontal regions. Age 0 year walleye Pollock E _wb changed in a non-linear fashion with fish size, with larger juveniles typically having higher E _wb. Size thresholds were identified at which the relationship between age 0 year walleye pollock E _wb and L _S changed. One such threshold was found at 46 mm where E _wb reached a local minimum. Another threshold was found at 80 mm beyond which E _wb tended to remain constant with size. Overall mass-length and E _wb-length residuals were highly correlated with each other ( r =0.73, P ≪0.0001). The slope of the regression, however, was higher for smaller fish. Possible mechanisms are proposed to explain the observed ontogenetic variation in nutritional status and the role of age 0 year walleye pollock late summer E _wb on survival over their first critical winter of life.     

Winter growth of juvenile plaice on the Port Erin Bay (Isle of Man) nursery ground

Juvenile plaice ( Pleuronectes platessa ) were studied in Port Erin Bay, Isle of Man, U.K. between September and March 1989/1990 and 1990/1991. Plaice (>90 mm) were tagged and individual growth rates calculated for the autumn, winter and over-winter time periods. During the study the population of fish >90 mm remained fairly stable both within a study season and between years. Autumn growth rates ranged from 0 to 0.39 mm day⁻¹ (mean₁₉₈₉=0.13 mm day⁻¹, mean₁₉₉₀=0.10 mm day ⁻¹) and winter 0 to 0.5 mm day⁻¹ (mean₁₉₉₀=0.11 mm day⁻¹ and mean₁₉₉₁=0.17 mm day ⁻¹). In general, growth rates were higher at higher mean seasonal temperatures. However, relative growth rate was significantly higher in the colder winter period of 1991 than 1990.     

Age, growth and reproduction of the barrelfish Hyperoglyphe perciformis (Mitchill) in the western North Atlantic

Otoliths ( n = 847) and gonads ( n = 817) were collected from barrelfish Hyperoglyphe perciformis that were captured by commercial fishermen in the waters off South Carolina and Georgia in 1995, 1997 and 2001–2006. Of the otoliths collected, 97% were aged successfully, and specimens sampled ranged from 5 to 85 years, with a median age of 12 years. The von Bertalanffy growth parameters yielded the equation: L_t = 857·8{1 − e^{−0·0985[ t −(−8·95)]}}, where L_t is fork length ( L _F) at time t . Through histological examination, 94% of the gonads assessed were assigned to a sex and reproductive class. Females spawned from September to May with a peak from November to January. Males spawned year round, but had a peak from September to April. The sex ratio (M:F) for this population was 1:1·34. The smallest mature female was 605 mm L _F and the youngest immature female was 697 mm L _F. Estimates of L _F and age at 50% maturity ( L ₅₀ and A ₅₀) for females were 660 mm L _F (95% CI = 633–667 mm L _F) and 6·08 years (95% CI = 3·50–7·27 years), respectively. The youngest mature male was 575 mm L _F and the oldest immature male was 762 mm L _F, and no estimates of L ₅₀ or A ₅₀ were made for males. It was determined that barrelfish exhibit the typical characteristics of long life span, slow growth and high age at maturity seen in other deepwater fishes, and that care should be taken to manage this species accordingly.     

Population structure and phylogeography of Aphyocypris kikuchii (Oshima) based on mitochondrial DNA variation

Aphyocypris kikuchii is a cyprinid species endemic to northern and eastern Taiwan and is the only primary freshwater fish native east of the Coastal Mountain Range. In total, 92 individuals of A. kikuchii from seven populations in three regions of the island were surveyed for mitochondrial DNA (mtDNA) variation. High haplotype diversity ( h = 0·989) and low nucleotide diversity ( π = 0·009) of mtDNA were detected. Negative values of Tajima's D and unimodal mismatch distributions probably reflect a history of recent demographic expansions from small populations. Three major haplotype clusters displayed geographically non-overlapping distributions, indicating a long-term isolation between regions. Hierarchical analysis of molecular variance showed significant genetic structuring among populations ( Φ _ST= 0·66). Significant haplotype heterogeneity was also detected among populations within regions ( Φ _SC= 0·41, P < 0·001) and among regions ( Φ _CT= 0·43, P < 0·05). Molecular clock estimates of coalescence in the three major mtDNA lineages indicated coalescence in the most recent common ancestor c. 0·11–0·39 million years ago. Haplotypes of cluster B nested as interior nodes in the haplotype network, indicating that migrations from Shueilian (SL) populations to the northern region (cluster A) and to the eastern region (cluster C) may have occurred independently. Lineages A and B + C should be managed as two distinct evolutionarily significant units, while the northern, SL and southern groups should be managed as separate management units.     

Abundance-depth relationship, condition factor and adaptive value of zooplanktophagy for red bandfish, Cepola macrophthalma

The abundance-depth relationship, condition factor and feeding of red bandfish, Cepola macrophthalma , were studied from trawl samples collected seasonally in 1986–1988 in the western Aegean Sea (Greece). The red bandfish comprised numerically 1.4% of the total fish catch. Its abundance ranged between 0 and 1362 individuals/h (mean = 57.7 individuals/h, + s.d. = 124.7). The relationship between the natural logarithm of the mean number of individuals/h, ln[( n /h) + 1], and depth, D in m, was found to be described by the following quadratic model:
Feeding intensity and condition factor were significantly ( P <0.05) lower in December and March, when annuli formation takes place, and significantly higher (<0.05) in June and/or September when reproduction takes place. The red bandfish is a zooplankton predator. Copepods and euphausids dominated by far its diet and made up 60.4% and 31.1 % by number, respectively. The remainder of the diet was shared by cladocerans, decapods, mysids, chaetognaths, amphipods, fish larvae and decapod larvae. Red bandfish has probably evolved a zooplanktophagus habitat because, by providing a relatively abundant food supply, it will neither limit its high linear growth in the first 4–5 years of life nor increase its predatory induced mortality.     

Hierarchical organization of genetic variation in the Costa Rican livebearing fish Brachyrhaphis rhabdophora (Poeciliidae)

I examined the geographic distribution of genetic variation in the livebearing freshwater fish Brachyrhaphis rhabdophora in northwestern Costa Rica as revealed by allozymes and mitochondrial DNA sequences. Allelic variability at 11 enzyme-coding loci surveyed across 12 localities revealed marked genetic differentiation among populations within drainages (0_P= 0.36) and among drainages within regions (0_D=0.17), but not between northern and southern geographic regions (0_R=– 0.02). Allozyme variation was hierarchically organized such that populations found within stream drainages were more similar to each other than to populations found in adjacent drainages, a result confirmed by cluster analysis. In contrast to the allozyme data, there was extremely little DNA sequence variation among populations in the mitochondrial control region (3 variable nucleotide positions out of 444 bp examined). The difference in genetic divergence between allozyme and mtDNA markers was unexpected and is discussed in terms of biogeographical colonization events and a molecular selective swéep on the mitochondrial genome, both processes that could explain the lack of mitochondrial variability in this highly subdivided species.     

Comparison of growth rate and formation of otolith increments in age-0 red snapper

For wild red snapper Lutjanus campechanus , mean otolith increment deposition rate after marking with oxytetracycline dihydrate (OTC) was daily (0.97 increments day⁻¹) when growth rates were fast (0.63 mm fork length, L _F day⁻¹), but were not daily (0.82 increments day⁻¹) when somatic growth was slow (0.2 mm L _F day⁻¹). For reared larvae ( n =8), increment deposition rates were daily (0.99–1.03 increments day⁻¹), and growth rates ranged from 0.6 to 0.9 mm L _F day⁻¹. Growth rate affected increment deposition rate as a threshold function, i.e. when growth rate was <0.3 mm L _F day⁻¹, deposition was less than daily, but above this level increment deposition did not exceed a daily rate. As growth rates increased increment widths increased. Examination of a sub-sample ( n =8) of the otoliths from the slowest growing wild fish by scanning electron microscopy did not increase increment counts. Because L. campechanus are late spring-early summer spawners, young fish can expect maximum growth due to warm summer temperatures. Thus, daily ageing methods should be well suited to this species.     

The population biology of tench, Tinea tinea (L.), in two gravel pit lakes

The populations of tench from two gravel pit lakes of contrasting habitat type were studied. The population density of tench from St Peter's Lake, which has abundant aquatic vegetation was 176 individuals ha⁻¹ (102.2 kg ha⁻¹) compared to 0.3 individuals ha⁻¹ (0.5 kg ha⁻¹) in the Main Lake which has very little aquatic vegetation. The results of ageing tench by scales, opercular bones and otoliths were compared; all three structures gave similar results up to 9 years of age, but thereafter there were difficulties in ageing using scales and care was needed in counting annuli. The oldest tench caught was 15 years old. Growth of male and female tench was similar and fitted the von Bertalanffy model; for female tench L_∞ = 573 mm, K =0.122 and for male tench L_∞ = 586 mm, K =0.114. Recruitment was variable and strong year classes occurred in years with warm summers.     

Studies on grayling, Thymallus thymallus L., in Llyn Tegid and the upper River Dee, North Wales.

Scale and length/weight data from 2071 Llyn Tegid grayling and 1803 River Dee grayling were used for age and growth determinations. The time of scale annulus formation varied from autumn in some years to spring in other years. Seasonal changes in length, weight and the condition factor were described. The main growth period was from spring to autumn with very little growth occurring during the winter. Annual growth in length was back-calculated from scale measurements, and von Bertalanffy's model was fitted to the resulting length for age data. Comparisons were made between the specific growth rates and ultimate lengths ( L_x ) of Llyn Tegid and River Dee grayling, and between the growth of male and female grayling. Males grew faster than females after the onset of sexual maturity. Calculated lengths were converted to weights using a combined length/weight relationship for Llyn Tegid and River Dec grayling. Changes were evident in this relationship throughout the life of the fish.     

Geography of sexual dimorphism in the tooth size of the red fox Vulpes vulpes (Mammalia, Carnivora)

Geographic variation in sexual dimorphism of tooth size was assessed for the red fox Vulpes vulpes (Linnaeus, 1758) across the whole northern range of the species. Twenty-one measurements of tooth size and skull length were taken from 2849 specimens (1577 males and 1272 females) originating from 12 Nearctic and 25 Palearctic localities. The index of sexual dimorphism was calculated as a quotient of the mean measure of certain characters in males by the respective mean in females ( M _m/ M _f). In the whole range, the males were larger than females and mean dimorphism index of tooth size ranged from 1.01 to 1.06. On average, the tooth measurements in males were 3.6% larger than in females. The highest dimorphism was observed in the canines. Dimorphism of tooth size was higher in the Palearctic than Nearctic. Statistically significant differences between regions were found for lengths of C¹, C₁ and M₁. In the Palearctic, higher values of the dimorphism indices were observed particularly in the southern parts of the Eurasian range of the red fox and in Great Britain. For a few metrical traits, sexual dimorphism indices presented significant relations to some geo-climatic variables. The geographic pattern of size dimorphism in the red fox seems to be shaped by sexual selection, intraspecific and interspecific competition and population density.     

Genetic differentiation in pikeperch (Sander lucioperca): the relative importance of gene flow, drift and common history

To investigate the relative importance of homogenizing factors, such as gene flow, and diversifying factors, such as drift, genetic variation in pikeperch ( Sander lucioperca ) in two Fennoscandian regions (North and South) was analysed with microsatellites. Allelic richness and the degree of differentiation were significantly higher in the North ( F _ST= 0·20) than in the South ( F _ST= 0·064). In northern areas, assignments of genotypes were almost exclusively to the population of origin, but in southern areas, the proportion of correct assignments was significantly lower. Most samples exhibited significant heterozygote deficits, and the level of relatedness was higher than expected from randomness. These combined results suggest that there has been more gene flow between populations in southern areas than in northern areas, where the importance of genetic drift has been greater. Effective population sizes were small ( c. 100) and did not differ between areas. The effect of a common history appears minor, and thus processes such as genetic drift and gene flow have been more influential in shaping the patterns of genetic diversity in this species.     

Growth rates of juvenile smalltooth sawfish Pristis pectinata Latham in the western Atlantic

The growth rates of juvenile smalltooth sawfish Pristis pectinata collected in Florida waters between 1999 and 2006 were investigated using length-frequency and tag-recapture data. Stretched total length ( L _ST) data from 144 smalltooth sawfish (690–4960 mm) and 28 recaptures (775–2150 mm) were used for the analyses. Both methods indicated that growth was rapid during the first 2 years after birth. The L _ST increased by 650–850 mm in the first year, and by 480–680 mm in the second year. Data for animals >2200 mm were limited, so growth beyond 2 years of age was uncertain. The von Bertalanffy growth parameters estimated from L _ST frequency data were L _∞= 6000 mm, K = 0·140 year⁻¹ and t ₀=−0·863 years. Growth rates over the size range for which tag-recapture data were available were similar to that from L _ST frequency data. The growth rates reported are substantially faster than those previously assumed for this species and may have important implications for the recovery of this endangered species. There are conflicting data regarding the growth rates of older P. pectinata which need to be resolved with more data from the wild population before a complete understanding of the conservation implications can be obtained.     

Age estimation, growth, maturity and distribution of the roundnose grenadier from the Rockall trough

This paper summarizes the history of commercial exploitation of roundnose grenadier Coryphaenoides rupestris in the North Atlantic. Length frequencies of C. rupestris in 1993, from 400 to 1200 m on the slopes of the Rockall trough indicate a reduction since the 1970s in the modal length of fish found at 700–1000 m. Ages ranged from 2 to 50 years for males and 2 to 60 years for females, with most between 10–38 years. Females attained a greater asymptotic pre-anus length ( L _∞=19.5 cm) than males ( L _∞=15.5 cm) and had a greater weight for a given age (male W _∞=761g, female W _∞=1132g). This species may have a protracted spawning period. Using pre-anus lengths, 50% of male fish were mature at 10 cm (ages 8–10) while 50% of female fish were mature at 12 cm (ages 9–11). At the greatest depths sampled the length frequency of fish was bimodal with a hiatus between 9 and 11 cm (ages 8–12). Highest catch rates occurred on the Donegal slope in September at a depth of 800–1000 m.     

Distribution, growth and mortality of young rough scad, Trachurus lathami, in the south-eastern Brazilian Bight

Distribution, growth and mortality of larval and juvenile rough scad Trachurus lathami Nichols, 1920, were studied, based on samples collected during December 1991 in the south-eastern Brazilian Bight. Young rough scad were widespread throughout the region surveyed, but spawning was more intensive in the northern area and tended to be greater in areas of low temperature and high salinity. The length class distribution of the rough scad larvae and juveniles ranged from 2.25 to 32.25 mm body length (BL), and the preflexion larvae of size categories from 2.25 to 3.25 mm BL were the most abundant. Net avoidance was detected for early larvae (2.25 mm length class) and for juveniles larger than 12.25 mm BL length class. Two models were applied to estimate growth and daily growth rate: a linear regression and a Gompertz curve. Both curves showed similar results and a good fit to the data. The mean growth rate estimated by linear regression was 0.44 mm per day (SD=0.008 mm). In small larvae up to 25 mm BL the linear and Gompertz curves showed similar estimated lengths. The hypothetical length at age zero ( L ₀) was estimated as 1.5 mm. The instantaneous daily mortality coefficient estimated from the slope of the regression of log-transformed values of relative production rates ( P _t/ d _t) against age ( t_i ) was Z=0.1888 for larval and juvenile rough scad. This corresponds to a daily mortality rate of 17.2%.