Genetic structure of silver Prussian carp <Emphasis Type="Italic">Carassius</Emphasis> (Superspecies <Emphasis Type="Italic">auratus</Emphasis>) (Linnaeus, 1758) colonies from the Middle Dnieper Basin

Population genetic structure of silver Prussian carp from the Middle Dnieper basin was established by means of biochemical gene marking and cytometric analysis. In addition to diploid goldfish Carassius auratus, which was the basic species of bisexual colonies, a number of biotypes of triploid silver Prussian carp C. gibelio were identified. These biotypes either formed isolated unisexual populations, or were an admixture to the bisexual colonies. In addition, in bisexual colonies, triploid females of non-clonal origin were identified. Despite the fact that all forms of C. gibelio reproduced by means of gynogenesis, some of them (C. gibelio-1) formed isolated unisexual populations, while the others (C. gibelio-2, -3, and -4) usually coexisted with C. auratus.     

Hybridization of crucian carp <Emphasis Type="Italic">Carassius carassius</Emphasis> (Linnaeus, 1758) in Ukrainian reservoirs and the genetic structure of hybrids

The hybridization of crucian carp Carassius carassius inhabiting polyspecific carp populations of Ukraine’s water bodies and the genetic structure of its hybrids were studied using biochemical gene marking and cytometry procedures. The widespread hybridization between C. auratus and C. carassius was justified by a large number of hybrids, which could form populations only represented by hybrid specimens. The hybrids of C. auratus × C. carassius were diploid, triploid, and, in exceptional cases, tetraploid. Females and males were presented in equal numbers and were most likely breeding by hybridogenesis. Alongside with that, some clonal hybrids of C. carassius × C. gibelio-1 were represented by tetraploid females, and one triploid female of C. carassius × Tinca tinca was found. Arguments are presented in favour of hybridization of alien C. auratus and endemic C. carassius and that this hybridization may appear as one of the mechanisms of replacement and suppression of the C. carassius species.     

Reproductive biology of albacore Thunnus alalunga

Reproductive variables in albacore Thunnus alalunga were evaluated by gonad histology in samples of 132 males (58–118 cm fork length, L_F) and 112 females (59–101 cm L_F) that were collected from the western North Pacific Ocean from 2001 to 2006. In the sex ratio examination, males greatly outnumbered females in large adult fish (L_F > 100 cm). Thunnus alalunga exhibited a protracted spawning period from March to September in the waters off eastern Taiwan and the Philippines, and the peak spawning activity occurred in March and April. Minimum sizes associated with the classification of mature fish were 78 and 83 cm L_F for males and females, respectively. In addition, the largest L_F of immature fish were 93 cm for males and 94 cm for females. The spawning frequency estimate in April was 1·7 days. Batch‐fecundity estimates of 21 females (89–99 cm L_F) ranged between 0·17 and 1·66 million eggs (mean ±s.d . = 0·94 ± 0·43). The relative fecundity estimates of the 21 females ranged between 9·2 and 92·4 oocytes g^?1 body mass (mean ±s.d . = 50·5 ± 22·8). The results presented in this study provide increased information regarding this species' reproductive‐related characteristics than are currently available in stock status determinations.     

Length–weight relationships of an invasive cyprinid fish (Carassius gibelio) from 12 Greek lakes in relation to their trophic states

The length–weight relationships of the cyprinid fish Carassius gibelio (Bloch, 1782) are described for the 12 most important lakes of Greece. Carassius gibelio is an allogynogenetic fish species, which was introduced into Greek lakes during the late 1970s. The values of the exponent b of the length–weight relationships ranged from 2.33 to 3.38, and varied with the trophic state of the lake. In eutrophic lakes these b values were significantly (P < 0.001) lower than in oligotrophic or mesotrophic lakes. Relationships between the b values and phosphorus concentrations were logarithmic: b = 1.37–0.13 log (PO₄‐P); total length, fork length and standard length were linear (in all cases: r² > 0.95). In most of the lakes, populations consisted of females, with the exception of Pamvotis, Doirani and Koronia lakes where a small proportion were males.     

Geographic variation in life-history traits of the endemic kite skate Dipturus chilensis (Batoidea: Rajidae), along its distribution in the fjords and channels of southern Chile

Life-history traits of kite skates Dipturus chilensis were examined from two regions (c. 2286 km apart) in the sheltered fjords and channels of southern Chile. A total of 482 and 403 specimens were collected from the southern fjords (c. 42–46° S) and the fjords of Chilean Patagonia (c. 51–54° S), from September 2003 to 2004, respectively. Vertebra marginal increment analysis indicated an annual deposition of growth rings which was completed during the winter months. For each region, von Bertalanffy growth parameters showed that females attained a larger asymptotic size, L_∞, had a lower growth coefficient, K, and lived longer than males. Growth analysis indicated that D. chilensis from the Patagonian fjords had a longer life span (females: 22 v. 21 years; males 19 v. 17 years), attained a larger L_∞ (females: 150 v. 136 cm; males: 122 v. 118 cm total length, L_T) and had a lower K value (females: 0·087 v. 0·104; males: 0·110 v. 0·116) than their counterparts in the southern fjords. Comparisons with previous studies indicated that D. chilensis from both southern and Patagonian sheltered fjords had larger L_∞, and grew more slowly than their counterparts from central-southern Chile (L_∞= 119–123 cm, K= 0·123–0·127), suggesting latitudinal variations in growth. Females attained sexual maturity later than males in both regions. For both sexes, lengths at 50% maturity (L_50%) between regions were similar (females: c. 103 cm; males: c. 87 cm L_T); however, D. chilensis from Patagonia appeared to mature 1 year earlier (females: 13 v. 14 years; males: 10 v. 11 years). Specimens from Patagonia had a lower ovarian fecundity than those from the southern fjords. An increase in the proportion of mature females and males during summer, suggests that the reproductive peak occurs in this season, and no regional differences were found. The size of the egg cases increased with maternal L_T and these were longer in Patagonia. The information provided here represents the first evidence of regional variations in life-history traits for elasmobranchs in the south-eastern Pacific.     

Reproductive parameters of the Pacific angel shark Squatina californica (Selachii: Squatinidae)

Reproductive characteristics of the Pacific angel shark, Squatina californica, were evaluated from 420 specimens obtained from the artisanal fishery in La Paz Bay, Gulf of California, Mexico. Females (99 cm, 6000 g) were larger than males (95 cm, 5000 g) in terms of both total length (L_T) and body mass (M_T). The overall sex ratio was significantly different from the expected 1:1, suggesting sexual segregation of mature individuals in La Paz Bay. Males had developed reproductive organs and calcified claspers from 72 cm L_T; the median size at maturity (L_T50) was 75·6 cm. In females, only the left ovary was functional and mature ovarian follicles were present from 77 cm L_T; the estimated L_T50 was 77·7 cm. For the 10 gravid females sampled, uterine fecundity was between two and 10 embryos. Mature, non‐gravid females with small and large ovarian follicles appeared simultaneously with gravid females with follicles that did not exceed 1·9 cm diameter.     

Inheritance of microsatellite DNA in bisexual gynogenesis complex of Fangzheng silver crucian carp,Carassius auratus gibelio (Bloch)

Five gynogenetic progeny groups of silver crucian carp Carassius auratus gibelio were produced and sex ratios (males:total progeny) of each of the progeny groups were analysed. About 110 males and 366 females were genotyped at 15 microsatellite loci for comparison with their parents to (1) verify the gynogenesis status of Fangzheng C. auratus gibelio, (2) detect the incorporation of paternal genetic material into the offspring and (3) study the possible association of genetic exchange at microsatellite loci with the existence of sex. The sex ratios in progenies of five groups were highly variable, but all had significant female bias. The sex ratio ranged from 0 to 0·37. Significant differences in the sex ratio within and between groups were also found. Microsatellite genotyping at 15 loci showed that 100 and 97% of the progeny shared the same genotype with the mother in four groups and in one group, respectively, confirming that gynogenesis is the general mechanism of reproduction in C. auratus gibelio. However, 0·63% of all offspring did show incorporation of paternal genetic material. No single loci tested were associated with the occurrence of male progeny, indicating unknown genetic mechanisms for sex determination in C. auratus gibelio.     

Reproductive aspects of the Atlantic angel shark Squatina dumeril in the southern Caribbean Sea

The maturity and reproduction of the Atlantic angel shark Squatina dumeril were assessed using 77 females (29·2–110·4 cm total length; L_T) and 269 males (58·7–108·2 cm L_T) harvested by artisanal gillnetters off Venezuela. The biased sex ratio implied segregation or sex‐specific gear selectivity. Based on the development of the reproductive tract, 50% L_T at sexual maturity (L_T50, mean ± s.e .) for females and males were estimated at 86·14 ± 0·64 and 81·55 ± 0·12 cm, respectively. Uterine fecundity ranged between one and six and with a maximum embryo size of 25·7 cm L_T. Gravid females were observed from August to December, including those close to parturition and while the gestation period was not confirmed, the size of ovarian follicles among some specimens implied protraction. The low fecundity of the species supports close monitoring of catches.     

Influence of environmental parameters on growth pattern and population structure of Carassius auratus gibelio in Eastern Ukraine

Population structure and growth parameters of Prussian carp (Carassius auratus gibelio) were studied in 12 freshwater ecosystems of the Donbass region (Eastern Ukraine). These ecosystems differed significantly with respect to their surface area, water transparency and annual concentrations of phosphorus and nitrogen. Amongst the studied ecosystems, diploid males and females as well as a smaller percentage of triploid females were found. The population structure of C. a. gibelio varied significantly in terms of the percentage of triploids and sex ratio amongst diploids. A considerable proportion of triploid females (>10%) was found in four ecosystems with intermediate surface area (38–50 ha) and relatively high growth rate of specimens. The sex ratio amongst diploids was significantly female-biased in seven of 12 ecosystems, including those where triploids were present in considerable numbers. The growth parameters of Prussian carp were significantly correlated with ecosystem characteristics, but the growth patterns of diploids and triploids were not significantly different from each other. The restricted distribution of triploid specimens suggests that the triploid form might counter diverse environmental challenges, whereas the diploid form of Prussian carp seems to be efficiently adapted to a wide range of ecosystem conditions.     

Estimated genetic parameters for growth‐related traits in large yellow croaker Larimichthys crocea using microsatellites to assign parentage

To estimate the heritabilities of growth‐related traits in large yellow croaker, Larimichthys crocea, three independent full‐factorial crosses were created by crossing four males × four females, seven males × three females and four males × three females (set 1, set 2 and set 3). At 13 months post‐hatch, the juveniles were collected from three cross sets and measured for body mass (M), standard length (L_S) and body height (H_B). In addition, the parentage of the juveniles was assigned by genotyping six or seven polymorphic microsatellite loci. Out of the 959 juveniles, 99·6% could be assigned to a single parental pair. Heritabilities of growth‐related traits were estimated for individual and combined sets with the pedigrees reconstructed by using microsatellite genotypes. The heritability estimates at 13 month‐old were 0·02–0·30 for M, 0·02–0·25 for L_S and 0·03–0·36 for H_B. These results showed that the heritabilities of M, L_S and H_B were different among three sets, which suggested that different breeding strategies should be adopted for different sets.     

Distribution and Cytogenetic Features of Triploid Males of Crucian Carp in Azov Basin

When studying uni-bisexual crucian carp (Carassius auratus gibelio) populations in the Azov basin in 1995–2000, we found triploid males, which constituted 2.5%, on average, of the total numbers of studied samples. The areas of nuclei of erythrocytes of triploid males were, on average, 1.35 times those in diploid males. At the same optical density of DNA, the sizes of mature spermatozoon heads in triploid males were, on average, 1.8 times smaller than in diploid males, as follows from the data obtained in summer 1996. The results of similar studies carried out during the period of natural spawning activity in 1997–1999 suggest that the sizes of spermatozoon heads in triploid males were, on the contrary, 1.5 those in diploid males. Triploid males were characterized by mosaicism of spermatozoon sizes and chromosome mosaicism in somatic cells. Electrophoretic analysis for the locus of transferrin confirmed the triploid status of this genetic group. The results of comparative crosses of crucian carps with different ploidy suggest a high fertilizing capacity of triploid males, as well as normal viability of their progenies. A distinct positive correlation (r = 0.73) was found between the numbers of triploid females and triploid males in mixed di-triploid populations. No significant correlation was found between males and females within di- and triploid forms.     

Life‐history characteristics of the large Amazonian migratory catfish Brachyplatystoma rousseauxii in the Iquitos region,Peru

The main life‐history traits of the dorado Brachyplatystoma rousseauxii, a large Amazonian catfish undertaking the largest migration known for a freshwater fish species (from the nursery area in the estuary of the Amazon to the breeding zones in the head waters of the western Amazon basin close to the Andes), were determined from a 5 year sampling of >15 000 specimens in the Peruvian Amazon. The breeding season occurred during the falling and low‐water periods, which is hypothesized to be an adaptation to maximize the chances of young stages to reach the estuary. The size at first sexual maturity was slightly larger for females than males, c. 91 and 83 cm standard length (L_S), respectively. Both males and females reproduce for the first time at >3 years old. The fecundity per spawning event ranged from 481 734 to 1 045 284 oocytes for females weighing 25 and 34 kg, respectively. Seasonal variations of body condition were similar among sexes, but differed between immature specimens that had a higher condition during the low‐water period and lower condition during rising waters, and mature individuals that showed the opposite pattern. The growth characteristics were estimated by L_S frequency analysis. For females, the best fitting models gave a mean birth date in August, during the height of the breeding cycle, with the following von Bertalanffy growth function parameters: L_S∞ = 153·3, K = 0·29 and t₀ =– 0·37 years. For males, the best fitting model gave a mean birth date in July, also during the height of the breeding period, with L_S∞ = 142, K = 0·30 and t₀ =– 0·36 years. At a given age, females were systematically larger than males and the size difference increased with age. The largest females sampled (148 cm L_S) was 11 years old and the largest male (134 cm L_S) was 9 years old. The mortality estimates were higher for males total (Z) = 1·34, natural (M) = 0·52 and fishing (F) = 0·82 than for females (Z = 0·98, M = 0·50, F = 0·48). The life‐history patterns of B. rousseauxii are discussed in light of the available knowledge about this species and the understanding of its complex life cycle.     

Life‐history traits of the long‐nosed skate Dipturus oxyrinchus

This work investigates life‐history traits of the long‐nosed skate Dipturus oxyrinchus, which is a common by‐catch in Sardinian waters. The reproductive variables were analysed from 979 specimens sampled during scientific and commercial hauls. Females (10·4–117·5 cm total length, L_T) attained larger sizes than males (14·5–99·5 cm L_T). To evaluate age and growth, a sub‐sample of 130 individuals (76 females and 54 males) were used. The age was estimated by annuli counts of sectioned vertebral centra. Four models were used for the length‐at‐age data: the von Bertalanffy, the exponential, the Gompertz and the logistic functions. According to the Akaike's information criterion, the Gompertz model seemed to provide the best fitting curve (L_∞ mean ± s.e. : 127·55 ± 4·90 cm, k: 0·14 ± 0·09, IP: 3·97 ± 0·90 years). The oldest female and male were aged 17 (115·5 cm L_T) and 15 years (96·0 cm L_T), respectively. Lengths at maturity were 103·5 cm for females and 91·0 cm for males, corresponding to 90% of the maximum observed length in both sexes. The monthly distribution of maturity stages highlighted an extended reproductive cycle, with spawning females and active males being present almost throughout the year, as confirmed by the gonado‐somatic index. Ovarian fecundity reached a maximum of 26 yolked follicles with a mean ± s.e. size of 19·7 ± 6·5 mm.     

Biological observations on the broadfin shark Lamiopsis temminckii (Carcharhiniformes: Carcharhinidae)

Biological information was collected from 214 individuals of the broadfin shark Lamiopsis temminckii measuring 418 to 1782 mm total length, L_T. Size at maturity (L₅₀) for females and males was estimated at 1430 and 1368 mm L_T, respectively, while mature and gravid females were observed from 1350 mm L_T with litter sizes 2–8 and size at birth 418–650 mm L_T. Analysis of stomach contents revealed a variety of prey, primarily crustaceans (54·0%), teleosts (42·7%) and cephalopods.     

Life history of the symbiotically luminous cardinalfish Siphamia tubifer (Perciformes: Apogonidae)

Characteristics of the life history of the coral reef‐dwelling cardinalfish Siphamia tubifer, from Okinawa, Japan, were defined. A paternal mouthbrooder, S. tubifer, is unusual in forming a bioluminescent symbiosis with Photobacterium mandapamensis. The examined S. tubifer (n = 1273) ranged in size from 9·5 to 43·5 mm standard length (L_S), and the minimum size at sexual maturity was 22 mm L_S. The number of S. tubifer associated during the day among the spines of host urchins was 22·9 ± 16·1 (mean ± s.d .; Diadema setosum) and 3·6 ± 3·2 (Echinothrix calamaris). Diet consisted primarily of crustacean zooplankton. Batch fecundity (number of eggs; F_B) was related to L_S by the equations: males (fertilized eggs) F_B = 27·5L_S ? 189·46; females (eggs) F_B = 31·3L_S ? 392·63. Individual mass (M; g) as a function of L_S was described by the equation: . Growth, determined from otolith microstructure analysis, was described with the von Bertalanffy growth function with the following coefficients: L_∞ = 40·8 mm L_S, K = 0·026 day^?1 and t₀ = 23·25 days. Planktonic larval duration was estimated to be 30 days. The age of the oldest examined individual was 240 days. The light organ of S. tubifer, which harbours the symbiotic population of P. mandapamensis, increased linearly in diameter as S. tubifer L_S increased, and the bacterial population increased logarithmically with S. tubifer L_S. These characteristics indicate that once settled, S. tubifer grows quickly, reproduces early and typically survives much less than 1 year in Okinawa. These characteristics are generally similar to other small reef fishes but they indicate that S. tubifer experiences higher mortality.     

Cytogenetic studies of Poecilia (Pisces)

Natural populations of triploid females resembling the gynogenetic teleost, Poecilia formosa (Girard), occur in northeastern Mexico where they intermingle with diploid populations of this species and the members of congeneric bisexual species such as P. mexicana or P. latipinna. Mitotic configurations from gill epithelial cells show 46 chromosomes for the diploid fishes, but 69 chromosomes for members of the triploid clones associated with P. formosa. Triploid females have erythrocytes that are significantly larger than those from diploid specimens and also show a roughly 50% elevation in the average DNA content of their somatic nuclei. Similar analyses of two functionally incompetent males of P. formosa, of a number of bisexual F₁ and F₂ hybrid offpsring from P. latipinna x P. mexicana, and of females from several other poeciliid species consistently show only diploid DNA levels and somatic chromosome complements where 22N=46. Demonstration of cytogenetic criteria by which females from triploid clones may be clearly distinguished from sympatric diploid specimens of P. formosa or P. mexicana leaves unresolved, for the present, problems of an appropriate systematic designation for natural populations of triploid gynogenetic fishes. The role of sympatric speciation in the evolution of poeciliid genomes is discussed in terms of alternative mechanisms to account for the persistence in nature of a vertebrate triploid of hybrid origin.This work was supported by grants from the National Science Foundation (GB 7393) and from the U.S. Public Health Service (GM 14644).Recipient of a Research Career Development Award from the U.S. Public Health Service (1 K3 GM 3455).     

Sexual size dimorphism in anadromous brown trout Salmo trutta

Anadromous trout Salmo trutta exhibits sexual size dimorphism (S_SD); females were larger than males in populations where male mean total length (L_T) at maturity was below 49 cm and females were smaller than males when mean male L_T was above 49 cm, the slope of the regression of female on male L_T was 0·59. In streams with mean annual discharge below 41 m³ s^?1, flow added significantly to a model with S_SD as the dependent variable and male mean L_T at maturity as the first predictor variable. There was a slight increase in S_SD with increasing latitude, which may result from an increase in male size with increasing latitude.     

Age and growth of black seabream Acanthopagrus schlegelii (Sparidae) in Hong Kong and adjacent waters of the northern South China Sea

Age and growth of the black seabream Acanthopagrus schlegelii (family Sparidae) from the northern South China Sea (NSCS) were studied by reading growth rings in sectioned sagittal otoliths. Ring formation frequency was determined to be annual by using marginal increment analysis. The von Bertalanffy growth function parameters were estimated as: L_∞ = 43.7 cm L_S; K =0.22 year; t₀ = ?1.59 years. Functional males are significantly younger than functional females, with sexually transitional individuals between the modal ages of males and females supporting protandry in this species. Males become sexually mature within 1 year and 50% age at sex change is at 2 years. The maximum age recorded for both males and females sampled was 9 years which is lower than for conspecifics elsewhere and may reflect high fishing pressure in the study area when compared with conspecifics in other areas or could reflect latitudinal effects. Otolith mass was significantly and positively related to age, providing a cheap and quick alternative method for approximating age. Acanthopagrus schlegelii is a relatively fast‐growing and rapidly maturing species attaining a similar asymptotic length to conspecifics. A need for fishery management is indicated to protect both young juveniles and older adults, especially females, to increase reproductive output and safeguard fishery production.     

Spontaneous polyploidy,gynogenesis and androgenesis in second generation (F2) koi Cyprinus carpio × goldfish Carassius auratus hybrids

The objective of this study was to characterize the genetics of second generation (F₂) koi Cyprinus carpio × goldfish Carassius auratus hybrids. Spermatozoa produced by a novel, fertile F₁ male were found to be diploid by flow‐cytometric analysis. Backcross (F₁ female × C. carpio male and C. carpio female × F₁ male) juveniles were triploid, confirming that female and male F₁ hybrids both produced diploid gametes. The vast majority of surviving F₂ juveniles was diploid and small proportions were aneuploid (2·1n–2·3n and 3·1n–3·9n), triploid (3n) and tetraploid (4n). Microsatellite genotyping showed that F₂ diploids repeated either the complete maternal or the complete paternal genotype. Fish with the maternal genotype were female and fish with the paternal genotype were male. This demonstrates that F₂ diploids were the result of spontaneous gynogenesis and spontaneous androgenesis. Analysis of microsatellite inheritance and the sex ratio in F₂ crosses showed that spontaneous gynogenesis and androgenesis did not always occur in equal proportions. One cross was found to have an approximate equal number of androgenetic and gynogenetic offspring while in several other crosses spontaneous androgenesis was found to occur more frequently than spontaneous gynogenesis.