Juvenile bisexuality in the red sea bream,Pagrus major

The histology of the gonad of the red sea bream,Pagrus major, was examined in order to study the early gonadal development, sexual maturation and sex ratio in a natural population. A total of 1,117 fish between the ages of 4 months and 8 years were examined. Gonads of 4-month-old fish were either sexually undifferentiated with a central cavity, or ovarian in form. Gonads of 12- and 18-month-old fish were ovaries or bisexual gonads, while those of 2-year-old fish were ovaries, bisexual gonads or testes. Fish aged between 3 and 8 years had ovaries or testes, except for a few bisexual gonads found in 3- and 4-year-old fish. The chronological appearance of females, hermaphrodites and males in that order, and histological evidence, suggested that the testis originates from the ovary via a bisexual gonad in the juvenile stage. The sex ratio of females to males at the age of 2 years and over was about 1:1, suggesting that hermaphroditic red sea bream appear in about 50% of the juvenile population. The sexual pattern in this species, therefore, is concluded to be gonochorism with a bisexual juvenile stage.     

The fish community of the Loosdrecht Lakes and the perspective for biomanipulation

In a two-year-study, the fish community of the Loosdrecht Lakes area was characterized with regard to the professional fishery and the forage base. The lakes are shallow (mean depth 2 m) and eutrophic to hypertrophic. The bream,Abramis brama, dominates the fish biomass. The pikeperch,Stizostedion lucioperca, is the main predator.Bream up to 30 cm have a slow growth rate and are in a bad condition. A faster growth rate and a better condition are shown by bream of 30 cm and more. The small bream feeds on chironomid larvae, benthic cladocerans and zooplankton. The better condition of bream over 30 cm is explained by the more efficient feeding of larger bream onChironomus plumosus larvae. Pikeperch show a fast growth rate and a good condition. Recruitment is limited by the low densities of smelt,Osmerus eperlanus, leaving cannibalism as the most important way for the 0+ pikeperch to become piscivorous and to manifest a fast growth.The impact of the professional gillnet fishery on bream and pikeperch is small because the mesh sizes in use are as large as 75–100 mm bar mesh.The planktivorous 0+ pikeperch consumes mainly the carnivorous zooplanktersLeptodora kindtii and cyclopoids. The zooplankton community lacks large herbivorous species likeDaphnia hyalina, capable of consuming bluegreens. A possible experiment in biomanipulation with a view to find out whether the development ofD.hyalina is depressed by the small planktivorous cyprinids, is predator enhancement with the aid of a stocking programme for indoor-raised 0+ pikeperch in early summer.     

Differences in the exploitation of bream in three shallow lake systems and their relation to water quality

SUMMARY 1. The development of bream populations, water transparency, chlorophyll‐a concentration, extent of submerged vegetation and densities of the zebra mussel, Dreissena polymorpha, were analysed in three shallow eutrophic lake systems subject to different fish management. 2. In Lake Veluwemeer, the bream population was reduced from c. 100 to 20 kg ha^?1 after 5 years of fishing. The mortality caused by the fishery was estimated at 38% of bream >15 cm in addition to a 13% natural mortality of bream >17 cm. The decline was followed by an expansion of the Chara beds present in the shallow parts, an increase in water transparency in the open‐water zone, an increase in the density of zebra mussels and a decrease in chlorophyll‐a concentrations. 3. The newly created Lake Volkerak showed trends opposite to those in Lake Veluwemeer. Bream colonised the lake in 1988 and reached a biomass of c. 140 kg ha^?1 in 1998. The water transparency decreased from a maximum of 3 m to c. 1 m and the chlorophyll‐a concentration increased from 5 to 45 μg L^?1. Submerged vegetation colonised up to 20% of the total lake area in the first 5 years after creation of the lake in 1987 but decreased to 10% as turbidity increased. 4. Seine fishery in the Frisian lake system did not appear to affect the bream population despite annual catches as high as 40–50 kg ha^?1. The estimated natural mortality of fish >15 cm was 15% and mortality by fishery was 26%. The high loss was apparently compensated by good recruitment and high growth rates resulting from a c. 1 °C higher water temperature during the years when bream were removed by fishing. There was only a slight decrease in chlorophyll‐a concentrations and a slight increase in water transparency. 5. The results of this study suggest that the effects of bream exploitation in eutrophic lakes can vary depending on the efficiency of the fishery, recruitment success and temperature regime. In the absence of fishery, bream dominated the fish community in the study lakes and apparently prevented D. polymorpha and submerged vegetation from establishing because of physical disturbance, enhanced internal P‐loading and resettling of resuspended sediments.     

State of the reproductive system of Cyprinidae from the Teterev River and Kiev Reservoir after the Chernobyl accident

The state of the reproductive system in four species of Cyprinidae from the Teterev River and Kiev Reservoir (Ukraine)—descendants of F₃–F₆ generations of individuals subjected to the radiation impact because of accident at the Chernobyl Nuclear Power Plant—has been studied. It was shown that 20 years after the accident, there is a wide range of morphofunctional anomalies of this system in fish. The most significant of them are asymmetry and abnormal morphology of gonads; proliferation of connective tissue-sterilization; and mass destruction of sexual cells of different stages of development. Disturbances of reproductive gonads among the studied species are expressed most strongly in bream Abramis brama and rudd Scardinius erythrophthalmus. In the series of studied generations, maximum frequency of occurrence of gonad anomalies in bream and silver bream Blicca bjoerkna was recorded in F₃–F₄ and that in roach Rutilus rutilus and rudd was recorded in F₄–F₅, which is determined by the phenomenon of prolonged mutagenesis.     

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.     

Host switch and infestation by Ligula intestinalis L. in a silver bream (Blicca bjoerkna L.) population

Sampling of the fish community was carried out for 20 years in the Mirgenbach reservoir, in North-Eastern France. The prevalence and the mean intensity of Ligula intestinalis (Cestoda) were analysed in roach (Rutilus rutilus) and silver bream (Blicca bjoerkna) populations, the main two infected species. The aim of this study was to investigate the host switch from roach to silver bream and the consequences of L. intestinalis infestation in silver bream, which is an unusual host for this parasite as Ligula parasitism in silver bream appears to be rare. We analysed in detail the relationships between parasitism index (PI), gonadosomatic index (GSI), perivisceral fat abundance (PFA) and condition index (CI) in the silver bream population. In 1998, prevalence of L. intestinalis highlighted a clear host switch from roach to silver bream. In the silver bream population, young fish were the most severely infected and the impact of plerocercoids appeared to be different depending on the host sex. In male silver bream, plerocercoids drew energy from fat reserves even if GSI was also slightly impacted. On the contrary, in females energy was diverted from gonad maturation rather than from perivisceral fat reserves. No significant difference was observed in terms of CI in either sex.     

On the biology of bream, Abramis brama (L.) in Lake Peipsi in 1994

The population of bream in L. Peipsi was studied with respect to age, growth rate, condition factor (according to Fulton) and length-weight relationship in 1994. That autumn the bream population in L. Peipsi consisted of fishes aged from 0+ to 15+. During the first year bream reached an average body length of 7.9 cm (the commercial legal size (30 cm) was usually attained by the end of the 5th–6th year. The condition of bream in this lake was above the average of Estonian lakes. The relatively good growth rate and condition of bream in the lake indicates that the waterbody is appropriate for this fish.     

Biology of the kingsoldier bream (Argyrops spinifer, Forsskål 1775; Sparidae), from the Arabian Sea, Oman

It is recognized by the FAO that management of fish resources in the western Indian Ocean is complicated by the lack of data on the basic biology and landing statistics for exploited fish species. In this paper data are presented on the population biology of kingsoldier bream, Argyrops spinifer (Forsskål 1775), in the Arabian Sea with a view to contributing towards the development of management plans for its sustainable exploitation. Samples were obtained from the Omani artisanal hand‐line fishery catch, January 2001–December 2002. Total length (L_T) of fish sampled ranged from 20 to 68 cm (males) and 25 to 70 cm (females). The male : female ratio was similar up to 55 cm L_T but the larger size‐classes were composed predominately of male fish. L_T/carcass weight (W_C) relations for male and female fish were similar and the combined data produced an equation W_C = 0.00005 × L_T^2.67. Marginal increment analysis indicated an annual cycle of opaque and translucent ring formation in otoliths that was related to the change in surface water temperature during the annual monsoon period. The opaque zone was completed in May and the translucent zone began to form in June. Female and male fish age ranged between 2 and 25 years. Both males and females exhibited similar asymptotic growth patterns; the combined von Bertalanffy growth function was L_t = 64.6(1 ? e^{[?0.142(t + 0.489)]}). Gonadosomatic indices and gonad condition of male and female fish indicated that the spawning season occurred between September and January. Size (L₅₀) and age at first maturity (A₅₀) were estimated to be 36.5 cm L_T and 5.0 years for males and 37.2 cm L_T and 5.6 years females, respectively. The results of this study provide fundamental information on the biology and population dynamics of A. spinifer in the Arabian Sea that can be used in management models for the continued sustainable exploitation of this species in the Omani demersal coastal fisheries.     

Age,growth and reproduction of the black sea bream Spondyliosoma cantharus (Linnaeus, ) (Sparidae) in the Gulf of Annaba (Algeria)

The objective of this study was to determine the basic population‐specific parameters necessary for fish stock assessment in the Gulf of Annaba and to compare these with data from other Mediterranean regions. Black sea bream Spondyliosoma cantharus (Linnaeus, 1758) (N = 501) were collected monthly from January to December 2008 along the Algerian eastern coasts. More than 22 fish were collected each month and ranged in size from 13.4 to 40 cm total length, weighing from 36 to 1080 g eviscerated weight. Biological sampling included weighing and measuring the fish, gonad weighing, sex and maturity stage determination, and age estimation through otolith readings. Validity of the otolith readings for estimating age and growth was supported using the back‐calculation method. Estimated parameters of the von Bertalanffy model are: L_∞ = 33.54 cm, W_∞ = 633.46 g, k = 0.52 year^?1 and t_o = ?0.04 year. The growth performance index (φ) is: 2.76. The length‐weight relationship is: EW = 4.4.10^?6 TL^3.23. The spawning period occurred from February to May, while the gamete emission peaked in April. Females reached sexual maturity at 19.3 cm (2 years) and males at 21.3 cm (3 years). Sexual inversion occurs at approximately 24.3 cm. Spondyliosoma cantharus was characterized as being a protogynic hermaphrodite.     

The food, growth and abundance of five co-existing cyprinids in lake basins of different morphometry and water quality

The food, growth and abundance of five co-existing cyprinid fish species in the eutrophic Lake Hiidenvesi were studied. The diet overlaps within the cyprinid community in shallow lake basins were compared with those in a deep basin, where littoral resources are less available. Roach, bleak and white bream inhabited both the shallow and the deep parts of the lake. Their growth rate was slow, probably due to the low availability of animal food, indicated by the increasing proportion of detritus and plant material in the diets towards the end of the summer. In the deep basin, roach and bleak, contrary to white bream, did not forage on the very abundant invertebrate Chaoborus flavicans, explained by the migration behaviour of C. flavicans. Blue bream, unlike other cyprinids, utilized copepods and had a relatively fast growth rate, but was mostly restricted to the shallow areas. The condition of the bream stock was weak both in terms of growth and abundance. The availability of zoobenthos was low and bream was not able to compete for zooplankton with the more specialized planktivores.     

Diapause in the life cycle of Calanoides carinatus (Kroyer), (Copepoda, Calanoida)

The distribution and stage composition of Calanoidescarinatus (Kroyer) are described together with changes in protein and lipid content, respiration rate and gonad development in copepodite stages IV and V (CV) and adults in the Northern Benguela current (17°S, 23°S and 25°S).During active upwelling the population consisted of two parts: the surface part over the shelf was represented by all development stages, while the deep part offshore was dominated (90–95%) by diapausal CVs. In the surface CVs the surplus assimilated energy was allocated to structural growth and maturation or to synthesis of reserve lipids. CVs with large oil sacs and high lipid content descended into deeper layers and formed diapausal stock; they were characterized by a dramatic decrease of respiration rate. Increase of gonad size in association with decrease of oil sac volume in diapausal CV suggests that reserve lipids were expended not only for respiration but also for gonad development. The moulting of dispausal CVs into adults took place in deep water.These results are discussed in relation to the life cycle of the C. carinatus population and the factors causing the formation and termination of the diapausal phase.     

Maximum length and age report of Sparus aurata (Linnaeus, 1758) in the Black Sea

The presence of gilthead sea bream (Sparus aurata) in the Black Sea, albeit sparse, has been known for many years. In recent years, it has been encountered in fishing nets, most commonly as by‐catch. In this study conducted in the southern Black Sea (Ordu) region, three female individuals were caught in trammel nets on October 9, 2017, and the largest individual was found to have a total length of 61.4 cm, a weight of 3080.6 g, and a gonad weight of 115.59 g. The metric and meristic characteristics of the largest individual sampled were also determined.     

Dynamics of structural parameters of populations of the bream <Emphasis Type="Italic">Abramis brama</Emphasis> (Cyprinidae) in Rybinsk Reservoir in 1954–2007

The data on age, size, and sex structure of the population, on the linear and weight growth of bream Abramis brama are generalized for the period of 1954–2007 in Rybinsk Reservoir. Analysis of dynamics of these parameters demonstrated that recently a high fishing intensity is both reflected on the size of the stock but also determines the changes in structural parameters of the bream population. At present, in the exploited stock of bream, the specimens of junior ages dominate. The part of specimens older than ten years, which previously made the bulk of catches, now compose not more than 10–15%. This resulted in a rather noticeable decrease of mean age and size in catches. The previously observed sex ratio, near 1: 1, shifted towards a significant prevalence of males. The age of the first spawning and of the fish spawning for the first time decreased. These changes indicate that the fishing load surpasses adaptational potential of bream.     

Reproductive features of the non-native Siganus luridus (Teleostei, Siganidae) during early colonization at Linosa Island (Sicily Strait, Mediterranean Sea)

In July 2003, the finding of a newly settled population of Siganus luridus at Linosa Island (Sicily Strait, Mediterranean Sea) gave us the unusual opportunity to examine the reproductive condition of a Lessepsian migrant during early phases of colonization. Aspects of gonad morphology, fecundity, atresia and oocyte dynamics were investigated by using 43 pioneer specimens collected in concomitance with their first record in the Pelagie Islands. Ovarian development was consistent with the group‐synchronous type, and testicular organization was of the unrestricted spermatogonial testis type, with cystic spermatogenesis. Both males and females had reached final stages of gonad maturation. The rates of follicular atresia were moderate: out of 17 adult females, 10 individuals did not present atretic oocytes; six exhibited <15.1% of secondary growth phase (SGP) oocytes in α‐atresia, while one female presented 45.7% of SGP in α‐atresia. Fecundity estimates did not diverge from what was observed in a reference population along the Lebanese coast. Absolute fecundity ranged from 115 739 to 740 433 oocytes per female (16.5–24.5 cm L_T). Relative fecundity ranged from 1239 to 3162 oocytes g⁻¹, with a mean of 1885 ± 868 oocytes g⁻¹. Our observations indicated that these early settled siganids are reproductively active at Linosa and suggested the forthcoming of self‐maintaining populations across the central Mediterranean area.     

Biomanipulation,new perspectives for restoration of shallow,eutrophic lakes in The Netherlands

Eutrophication of Dutch lakes has led to massive algal growth, disappearance of most of the macrophytes and disturbance of the food chain. The pike population has fallen sharply and bream developed very strongly, in the absence of this predator. Eutrophication problems are primarily being tackled by reducing nutrient loading. Restoration of water quality, however, seems to be impeded by the present structure of the food chain,i.e. the large bream stock. Biomanipulation, especially fish stock control with the aim of reducing the bream stock and increasing that of predatory fish, can accelerate the process of restoration. For the further development of biomanipulation it is very important that water authorities and managers of fish stocks agree on a common strategy.     

Characterizing the biological traits and life history of Acanthopagrus (Sparidae) hybrid complexes: implications for conservation and management

This study examined the spatio‐temporal reproductive patterns, population structure, maturity and growth of Acanthopagrus hybrid complexes, which comprise mainly black bream Acanthopagrus butcheri and the hybrids they form with yellowfin bream Acanthopagrus australis, in two Australian estuaries (Coila and Brou Lakes, NSW). There were no differences between pure A. butcheri and hybrids in terms of their population structure, growth and maturity, suggesting that these two breeds have similar life histories and may therefore be managed as single, naturally cohesive units. Sexual variation in size structure was only observed for the complex in Coila Lake. Although there was significant variation in age structure between estuaries, both complexes exhibited dominance of only a few year classes indicating episodic recruitment and high fishing mortality. Acanthopagrus eggs occurred in higher numbers within upstream creek habitats compared to lake habitats, thereby highlighting the need to protect these spawning habitats. Although maturity in the complexes was not influenced by gender or estuary, differences in growth were detected between the genders and estuaries.     

Mytilus galloprovincialis (Mollusca: Bivalvia) in a warm-temperate South African estuarine embayment

The distribution, population structure, condition and gonad indices, and the attachment strengths of the invasive Mediterranean mussel Mytilus galloprovincialis are described from the Knysna Estuary, South Africa. Mussels were found in the rocky intertidal at the mouth of the estuary and on all man-made hard substrata as far as 12?km from the mouth in 2013. However, mussel beds were found only in the lower reach of the estuary, where mussel densities were as high as 120 per 0.01?m². When compared to mussels from the embayment regions of the estuary, those at the estuary mouth, where wave action was high, were generally smaller, had significantly lower condition and gonad indices, and greater attachment strength. This suggests that mussels within the sheltered regions of the estuary invest more energy in growth and reproduction, and that this is one reason for their success as an invasive species in the Knysna estuarine embayment.     

Isolation and characterization of polymorphic microsatellite loci in Wuchang bream (Megalobrama amblycephala)

Wuchang bream (Megalobrama amblycephala) is an economically important fish in China. From a (GT)₁₃‐enriched genomic library, 20 microsatellites were developed. Nine of these 20 loci were polymorphic in a test population with allele numbers ranging from two to four, and the observed and expected heterozygosities ranging from 0.2609 to 0.7826 and from 0.3739 to 0.7546, respectively. In the cross‐species amplifications, six of these nine loci were also polymorphic in white amur bream (Parabramis pekinensis). These polymorphic microsatellite loci are potentially useful for population genetics of Wuchang bream and its closely related species.     

Annual reproductive cycle and growth of the pen shell Atrina maura (Pterioidea: Pinnidae) on sand-bottom culture in the Ensenada Pabellones lagoon system,Gulf of California,Mexico

Abstract

The reproductive cycle and growth of the pen shell, Atrina maura, which was cultured in the Ensenada Pabellones lagoon system, Gulf of California, from March 2008 to March 2009, is described in this article. Histological techniques and the condition index were used to determine its reproductive condition. The sex ratio was 0.57 females:1.72 males within the population studied. There were no differences (χ², p < 0.05) in shell length (SL) between males and females. The mean length of the sampled specimens ranged between 50.99 ± 4.86 mm and 218.16 ± 8.87 mm. The histological results confirmed that A. maura is a gonochoristic organism that presents synchronic development of the gonads. The maturity and spawning phases were observed throughout the study period, with the exception of March and May 2008. The frequency of the gonad development stages obtained per month suggests that this species reproduced two times annually, with one important reproductive period from June to September, a minor reproductive period from November to February, and two resting periods as follows: July to August and January to February 2009.     

Photoperiodic activation of brains in castrates and the role of the gonad in reproductive maturation ofLimax maximus

Summary Results obtained with castration and gonad implantation verify that a factor(s) from the gonad is required for development of the female accessory sex organs (ASO) inLimax maximus. In addition, they show that a gonadal factor promotes rapid gonadal growth and sperm production, and gradual or incomplete development of the penis. Although an immature slug that is castrated and then switched to inductive photoperiods fails to exhibit reproductive tract maturation, in two differently designed experimental tests, the brains of such animals were able to promote sexual maturation when subsequently paired with an immature gonad. We interpret the results of these experiments as evidence for photoperiodic induction of secretion of maturation-inducing factor (MH) by the brain in the absence of the gonad. One or more gonadal hormones appear to be both necessary and sufficient for production of sperm and for development of ASO, but they are not required for the photoperiodic stimulation of MH release.Abbreviations ASO accessory sex organs - MH maturation hormone