Seasonal distribution, age, growth, and reproductive biology of marbled sole Pleuronectes yokohamae in Tokyo Bay, Japan

ABSTRACT:   The seasonal distribution, age, growth and reproductive biology of marbled sole Pleuronectes yokohamae (Günther) from Tokyo Bay, Japan were studied. A clear seasonal distribution trend was observed, with P. yokohamae limited to the south of the bay in summer and expanding almost throughout the bay in other seasons. The formation and dynamics of hypoxic areas in the bay limited the northward distribution of P. yokohamae in summer. Age was determined by counting growth rings on otoliths; maximum ages were found to be 5 years for males and 6 years for females. The mean back-calculated length for females at each estimated age was greater than that for males. Growth of males and females was shown by the von Bertalanffy growth equations. Reproductive biology was studied on the basis of gonadosomatic indices and histological sections of gonads. The spawning season lasted from November to March, peaking in December and January. Sixty per cent of males at 1 year and all males ≥ 2 years had mature testes, whereas 6.7% of females at 1 year, 58.3% of females at 2 years, and all females ≥ 3 years had attained maturity.     

Ichthyoplankton distribution and abundance in relation to nearshore dissolved oxygen levels and other environmental variables within the Northern California Current System

Nearshore hypoxia along the coast of Oregon and Washington is a seasonal phenomenon that has generated concern among scientists studying this temperate upwelling ecosystem. These waters are affected by coastal upwelling‐induced hypoxia mainly during late summer and fall, but the effects of low oxygen levels on fish and invertebrate communities, particularly during the early‐life history stages, are poorly known. We investigated the effects of hypoxia and other variables on the species composition, density, vertical and horizontal distribution of fish larvae along the Oregon and Washington coasts during the summers of 2008, 2009 and 2010. Bottom‐dissolved oxygen (DO) values ranged from 0.49 to 4.79 mL L^?1, but the overall water column DO values were only moderately hypoxic during the 3 yr of sampling compared with recent extreme years. In this study, DO was found to be an environmental parameter affecting the species composition, but other variables such as season, year and depth of capture were also important. Although the overall density of fish larvae increased with increasing bottom‐DO values, the effect on individual species density was limited. Slender sole (Lyopsetta exilis) and sand sole (Psettichthys melanostictus) were the only species to have a weak trend of density with DO, but both showed negative relationships and neither relationship was significant. Our results indicate that larval fish spatial distribution was only moderately affected within the range of observed oxygen values, but low DO may be an important factor under intense hypoxic conditions.     

The life-history patterns of Barbus bocagei sclateri (Günther, 1868) in a tributary stream of the Guadalquivir River basin, southern Spain

Abstract– The age, growth and reproduction of Barbus bocagei sclateri (Günther, 1868) were studied from November 1987 to September 1989 in a tributary stream of the Guadalquivir River basin. The maximum ages observed were 8 + in males and 11 + in females. The seasonal growth began in April and lasted 4–6 months. The males matured during their third year of life (2 +) and females during their fifth/sixth year (4 +/5+). There was a significant difference in the overall sex ratio of 1. 3: 1 (961 males to 740 females). Reproductive activity started in April/May and lasted until June/July. The end of the reproduction period coincided with a fall in the percentage of oxygen saturation. During this reproductive period, females spawned 2 batches of eggs. The relationship between fecundity (Fec) and fork length (FL, mm) was: Fec= 7.54 × 10⁻⁴ FL^3.06 The maximum contribution to the fecundity of the population was observed in the 6 + female group. The reproductive effort was also maximum in this age. Compared with the rest of the European barbel populations studied, the life-history patterns of this stock are characterized by low annual growth, early maturity, reduced longevity and high fecundity.     

Reproductive biology of<Emphasis Type="Italic"> Pasiphaea japonica</Emphasis> females in Toyama Bay,central Japan

The reproductive biology of female Pasiphaea japonica, including the minimum size of females carrying embryos, spawning and hatching seasons, and brood size, was examined in Toyama Bay, central Japan, during 2004 through 2007. Sampling was conducted onboard a commercial seiner and a fisheries research vessel. The minimum size of ovigerous females was 47.7 mm body length. The percent occurrence of ovigerous females increased with body size, reaching 50% at 57.9 mm body length. Ovigerous females occurred all year round with a seasonal change in percent occurrence, ranging between 41.5 and 94.3% of the total observed females. Consequently, reproduction in females seems to occur throughout the year in Toyama Bay, with seasonal differences in reproductive intensity. Spawning intensity was high during April–July and October–January based on the occurrence of the early developmental stage of embryos, while hatching intensity was high in October–May based on the occurrence of embryos just before hatching. Brood sizes were similar at the same size of body length regardless of embryo stage, except just after spawning.     

Demersal fish and invertebrate biomass in relation to an offshore hypoxic zone along the US West Coast

In August 2007, as part of the NOAA National Marine Fisheries Service (NMFS) West Coast Groundfish Bottom Trawl Survey, we examined the biomass of demersal organisms in a known hypoxic area off the Oregon coast. Although observed each summer, the intensity of hypoxia has varied annually (2002–2007) with the greatest temporal and spatial extent noted in 2006. In 2007 we identified the geographic extent of the hypoxic zone and sampled 17 stations along two depth contours (50 and 70 m) within the area. A Sea-Bird SBE 19 plus equipped with a dissolved oxygen (DO) sensor was attached to the bottom trawl to monitor oxygen concentration during each tow. Bottom DO concentrations at all stations were hypoxic with means along the tow tracts ranging from 0.43 to 1.27 mL L⁻¹. Total catch per unit effort (ln CPUE, kg hectare⁻¹) and species diversity (number of species, N ) were significantly and positively related to oxygen concentration along the hypoxic gradient. In addition, CPUE (natural log-transformed) for eight fish species and five benthic invertebrate species were significantly and positively related to bottom oxygen concentration within the hypoxic region. Condition factors for five fish species, as well as Dungeness crab ( Cancer magister ) increased with increased bottom oxygen levels along the hypoxic gradient. Historical catch (2003–2006) within the hypoxic zone indicates that biomass was significantly lower in 2006, the year with the lowest bottom DO levels, relative to other years.     

Reproductive biology of male skipjack tuna <Emphasis Type="Italic">Katsuwonus pelamis</Emphasis> (Linnaeus) in the tropical western and central Pacific Ocean

The reproductive biology of male skipjack tuna Katsuwonus pelamis was examined from May 2005 to December 2007 in the tropical western and central Pacific Ocean. Testis maturity was classified into five stages (i.e., immature, early maturation, mid maturation, late maturation, and regression) on the basis of morphological changes in the germinal epithelium. The testis duct system (TS), which was characterized by lobules that lack spermatocysts, store only sperm, and form an anastomosing network, was located under the main sperm duct. The TS was observed at all stages of maturity except the immature stage, and first appeared in individuals with a fork length (FL) of 38–40 cm. The estimated minimum size at first maturity was 35.5 cm FL and the size at 0.5 maturity was 40.7 cm in FL. It was difficult to clearly differentiate the testis maturity stage based solely on the gonad index (GI) class because each GI class contained mature fish. Monthly changes in testis height index and GI did not follow a seasonal cycle. Mature individuals dominated throughout the year. These results imply that male skipjack tuna in this area showed evidence of spawning activity throughout the year without a clear seasonal pattern.     

Habitat use of cownose rays (Rhinoptera bonasus) in a highly productive,hypoxic continental shelf ecosystem

Highly productive surface waters and hypoxic (dissolved oxygen, DO ≤ 2.0 mg L^?1) bottom waters develop seasonally on the northwestern Gulf of Mexico continental shelf due to nutrient and freshwater inputs from the Mississippi‐Atchafalaya River system. We investigated the spatial distribution of the cownose ray (Rhinoptera bonasus), a highly mobile, bentho‐pelagic species that is a seasonal resident of the shelf, in relation to surface chlorophyll, bottom‐water hypoxia, and other environmental variables (salinity, temperature, depth). We used synoptic trawl and aerial surveys to investigate ray distributions at both shelfwide (100–1000s km) and local (5–50 km) spatial scales. Shelfwide sampling indicated that rays were associated with regions of high surface chlorophyll and low bottom salinity and DO, conditions characterizing the Mississippi‐Atchafalaya plume region. Local sampling in and around the hypoxic zone indicated that rays preferred habitats where bottom waters were hypoxic but they primarily occupied normoxic (DO > 2.0 mg L^?1) waters above the bottom hypoxic layer. Stomach fullness and diet composition were similar between rays sampled in habitats with hypoxic versus normoxic bottom waters. These results indicate that cownose rays are strongly associated with riverine‐influenced regions of the shelf and preferentially use habitats with hypoxic bottom waters, perhaps for benthic foraging. Collectively, our results highlight the importance of considering the responses of mobile species to enhanced productivity and to hypoxia‐induced habitat degradation, which are both the products of coastal eutrophication.     

Temperature and food‐level effects on reproductive investment and egg mass in vendace,Coregonus albula

Abstract Individual variation in reproductive investment is important for recruitment and population dynamics in fish populations. Thus, it is crucial to understand how these decisions are influenced by environmental conditions. Here, the influence of growth variation during gonadogenesis or early life on reproductive investment in vendace, Coregonus albula (L.) was investigated. A set of cohorts of mature females were sampled over two different years with contrasting climate conditions and food levels, using total length at age 1 year as a proxy for juvenile growth. Relative reproductive investment and individual egg mass were lower in the favourable year (elevated temperatures and zooplankton densities) when the females were in better condition compared with a less favourable year (lower temperatures and zooplankton densities). Female vendace demonstrated plasticity in their allocation to relative reproductive investment and egg mass, probably induced by diverging environmental conditions. This phenotypic response to growth may have strong effects on recruitment and population growth rate.     

Growth and maturation in sterlet <Emphasis Type="Italic">Acipenser ruthenus</Emphasis> under high concentrations of dissolved oxygen

This study investigates the effect of high dissolved oxygen concentrations (DO) on sterlet Acipenser ruthenus maturation. Two groups, each comprising 246 individuals of 8-month-old juvenile sterlets, were reared for 37 months under high DO (group H, mean DO of 11.2 mg/L) or normal DO (group C, mean DO of 7.3 mg/L). Significant differences in body weight were observed between group H (638.7?±?191.9 g) and group C (572.2?±?151.9 g) in 12 months (P?<?0.05). Growth until 12 months occurred at a specific growth rate of 0.6%/day for group H and at 0.5%/day for group C. The food conversion rate of groups H and C was 5.2 and 5.8, respectively. The gonadosomatic index of group H was 3.1?±?1.1 for females and 3.1?±?9.7 for males, and showed no significant difference with group C (3.0?±?0.7 for females and 2.8?±?8.9 for males, P?>?0.05) in 24 months. Significant differences in follicle diameter in mature females were also observed. Group H included 68 mature females, with an average follicle diameter of 2318.0?±?175.3 µm, whereas group C included 56 mature females, with a smaller average follicle diameter of 2152.3?±?287.0 µm (P?<?0.001). However, the polarization index in group H (0.194?±?0.049) was higher than that in group C (0.178?±?0.042) (P?<?0.05). These results suggest that, for sterlet, rearing conditions with high DO can affect growth of both the body and follicle diameter of fish compared to normal rearing conditions.     

溶解氧对团头鲂耐低氧新品系F5代的鳃组织形态及各组织酶活性的影响

为研究不同浓度溶解氧(DO)对团头鲂(Megalobrama amblycephala)耐低氧新品系F5代鳃组织形态以及各组织酶活性的影响,本研究将团头鲂在低氧[DO为(1.7±0.2) mg/L]和高氧[DO为(19.3± 0.5) mg/L]条件下分别处理0、4和7 d,恢复常氧[DO为(7.8±0.3) mg/L] 7 d后,通过石蜡切片观察鳃组织的形态,并测定了鳃、肝胰腺、肠道、肌肉中过氧化氢酶(CAT)、琥珀酸脱氢酶(SDH)及乳酸脱氢酶(LDH)活性和丙二醛(MDA)含量。石蜡切片结果显示,随着低氧处理时间的延长,团头鲂新品系鳃丝的层间细胞团体积减小,鳃小片表面积增加,恢复常氧7 d后又有所恢复。高氧条件下,层间细胞团体积增大,鳃小片表面积减小,恢复常氧7 d后也会恢复。酶活性检测结果显示,在低氧和高氧2种条件下,随着处理时间的延长,CAT活性和MDA含量在各组织中的变化无明显规律,但均有显著差异(P<0.05)。低氧条件下,LDH活性显著增高,SDH活性显著降低(P<0.05)。高氧条件下,LDH活性显著降低,SDH活性显著增高(P<0.05)。本研究可为溶解氧对团头鲂的鳃组织以及各组织酶活性的影响提供基础资料,并为团头鲂新品系的养殖与选育奠定基础。     

Reproductive characteristics of the orbiculate cardinalfish <Emphasis Type="Italic">Sphaeramia orbicularis</Emphasis> in the Chuuk Lagoon,Micronesia

Detailed knowledge of the reproductive characteristics of fish in tropical areas is currently lacking. We have performed a histological study of the reproductive aspects of Sphaeramia orbicularis, a tropical fish found on the Weno Islands of the Chuuk Lagoon, Micronesia, and further estimated the gonadosomatic indices (GSI) of this fish. The sex ratio was approximately 1:1. The standard length of males and females at 50% maturity was 49.0 and 46.9 mm, respectively. Histological observation of S. orbicularis ovaries and testes revealed that the fish exhibits multiple spawner characteristics, including coexistence of primary yolk stages, migratory nucleus or mature stages, and asynchronism of the spermatogenesis process. Monthly variations in the GSI and gonadal maturity stages demonstrated that reproductive activity occurs throughout the year. The findings in this study provide important information on the spawning activity and season of S. orbicularis in Micronesia.     

低氧预适应对魁蚶在低氧胁迫下生理生化指标的影响

本研究以未进行低氧预适应的魁蚶(Scapharca broughtonii)为对照组(C组),分析了2次低氧预适应(H2组)和4次低氧预适应(H4组)的魁蚶在溶解氧(DO)约为2.0 mg/L低氧胁迫48 h内的摄食、呼吸代谢和酶活力的变化规律。结果显示,3组魁蚶的摄食率(IR)在胁迫初期急剧下降,后期均随时间的延长逐渐恢复,至48 h时,H组恢复程度显著高于C组(P＜0.05＝;C组、H2组和H4组魁蚶的耗氧率(OR)随时间变化呈逐渐升高的趋势,48 h比0 h分别提高了1.15、1.08、0.73倍;3组排氨率(NR)表现出不同的变化趋势,至48 h时,C组、H2组和H4组分别为0 h的1.67、1.30、0.97倍;C组的氧氮比(O/N)相对平稳,H组的变化范围相对较大。3组的细胞色素C氧化酶(COX)随着低氧胁迫时间的延长呈逐渐降低的趋势,乳酸脱氢酶(LDH)活力和还原型谷胱甘肽酶(GSH)含量整体呈上升趋势,与对照组相比,预低氧组的酶活力在低氧胁迫期间变化相对平稳,应激反应小。研究表明,魁蚶经低氧预适应后再次受到低氧胁迫时,IR升高,OR降低,酶活性相对稳定,低氧预适应能提高魁蚶的耐低氧能力。本研究丰富了魁蚶低氧耐受相关研究的基础数据,为进一步探讨魁蚶低氧耐受机制和创制耐低氧新种质提供了参考资料。     

Patterns of oxygen production and consumption in intensively managed marine shrimp ponds

Abstract. Temporal trends were determined for primary production and respiration in marine shrimp ponds. Dissolved oxygen concentration (DO) and water temperature were monitored in four marine shrimp, Penaeus vannamei Boone and P. monodon Fabricius , ponds during the grow-out. Wind speed was also measured. Pond production and respiration were estimated based on DO curves. Trend analysis revealed a significant decline in pond net production during grow-out. Ponds were autotrophic at the start of grow-out but heterotrophic at the end. Pond respiration, adjusted for water temperature, increased during grow-out. Temporal trends in pond gross production appeared to be influenced by seasonal patterns in solar radiation intensity. Pond sediments and water column were the chief consumers of oxygen in the pond, accounting for 51% and 45%, respectively, of the total pond oxygen consumed. Despite showing a marked increase during grow-out, shrimp respiration rate was of relatively minor importance in the pond oxygen budget. Pond management strategies to maintain positive pond net production and to mitigate the impact of sediment respiration on pond DO were recommended.     

Population age and sex structure of Aphanius fasciatus Nardo, 1827 (Pisces: Cyprinodontidae) in the Mesolongi and Etolikon lagoons (W. Greece)

The population structure of Aphanius fasciatus in the Mesolongi and Etolikon lagoonal system was studied, using 5794 fish. Significant differences were observed in the number of individuals of each sex, the age and size composition and survival. The overall males to females sex ratio was 1:2.44, although there was seasonal variation. During the reproductive period the percentage of males in the population decreased significantly, while after reproduction and during recruitment they increased. The females in each age class were larger than the males (40.33 mm and 36.72 mean total length for females and males, respectively). The survival rate of females was greater than males (0.73 for females and 0.60 for males). The strategy of this species is to invest in female individuals.     

Feeding,body condition and reproductive investment of Astyanax intermedius (Characiformes,Characidae) in relation to rainfall and temperature in a Brazilian Atlantic Forest stream

Life history theory seeks to explain how environmental variation selects for patterns of investment in growth and survival relative to production and survival of offspring. Seasonal variations in rainfall and temperature provide environmental cues for spawning by many tropical freshwater fishes. To investigate environment–life history associations, we conducted a one‐year study of Astyanax intermedius in an Atlantic Forest stream of southeastern Brazil. Our analysis focused on temporal variation in feeding, body condition and reproduction in relation to rainfall and water temperature. For mature females, food intake was not significantly correlated with rainfall or temperature; however, body condition was negatively correlated with rainfall and water temperature. Female reproductive effort was positively correlated with water temperature, but did not vary with rainfall. For males and juveniles, there was no significant relationship between food intake or body condition and either environmental variable. Testis weight was negatively correlated with rainfall, but was not significantly correlated with water temperature. We detected a negative correlation between gonad mass with body condition and food intake for females but not for males. Our results differed from other studies in tropical and subtropical areas where rainfall has been shown to be positively correlated with fish reproductive effort. Our results indicate that reproductive effort of males is relatively constant throughout the year, whereas for females, it increases with increasing water temperature. This increase in reproductive investment in concert with an increasing temperature and metabolic rate may incur a trade‐off with somatic growth and survival for this small stream fish.     

大鹏澳养殖水域溶解氧的变化及其与生态结构的关系

根据2001年6月至2002年6月大鹏澳网箱养殖水域周年的溶解氧(DO)水平监测数据,阐述网箱养殖区水体DO的水平、季节的变化、垂直变化和网箱养殖水体DO质量评价以及DO与水环境因子的相关性。结果表明,大鹏湾网箱养殖水域DO周年水平为3 86～8 01mg/L,氧饱和度为51 6%～103 6%,养殖水域DO水平低于非养殖水域的;冬、春季DO水平较高,均符合我国渔业水质标准要求。夏季DO水平普遍较低,超标率为95%;表层水DO水平略高于底层水,DO水平超标率分别为46%和66 7%;DO水平(全年)与pH值、盐度、叶绿素水平均呈显著性正相关(P<0 02,n=32),与水温、无机磷和无机氮水平呈显著性负相关(P<0 02,n=32)。其中,在春季相关最为明显。     

Characterization of the quality of the gametes and sex steroid levels during spring and summer spawning events in pejerrey Odontesthes bonariensis reared under natural conditions of temperature and photoperiod

Pejerrey Odontesthes bonariensis spawning period takes place during the end of winter and spring and, depending on temperature conditions, during late summer and autumn. Nevertheless, the occurrence and quality of the summer–autumn spawning period have not been well documented and are not considered for aquaculture production. In this context, this study aimed to characterize the reproductive activity of pejerrey reared in captivity under natural conditions of temperature and photoperiod throughout a year in order to summarize the spawning quality of the two spawning periods. The present results showed that pejerrey might spawn from late winter to the end of the spring with a peak in October (mid‐spring) and, also during summer and early autumn, interrupted by a period of 56 days without spawning activity in between. The extension of both spawning periods was almost equal (67 and 69 days). Nevertheless, higher relative fecundity and larger egg size were observed during the first spawning period, associated with higher levels of oestradiol measured in females demonstrating that it is better than the second spawning. The fertilization rate was not affected throughout the reproductive periods. These differences in the reproductive parameters are discussed in order to design specific strategies to increase seed production.     

Impact of long‐term dietary exposure to lead on some reproductive parameters of a female Common carp (Cyprinus carpio L.)

During a long‐term 3‐year dietary exposure of mature carp females to lead, its bioaccumulation in the brain, changes in the neurohormonal activity at the level of the hypothalamus and the pituitary gland as well as the growth and maturation of ovaries were analysed. Moreover, an analysis of the effectiveness of hormone‐stimulated spawning during two subsequent spawning seasons was carried out. The results of the analyses show that chronic exposure of maturing and mature carp females to lead in feed results in its accumulation in the brain (1.365 μg g^?1). This impairs the endocrine activity of the hypothalamus, which is manifested by, among others, an increased secretion of dopamine and impaired spontaneous secretion of luteinizing hormone (LH). The observed decrease in the concentration of gonadotropin in blood inhibits vitellogenesis, which is manifested by a lower degree of the maturity of oocytes, lower fecundity (as measured by egg number, egg weight, egg maturity and egg survival) and lower gonadosomatic index values. The final negative impact of lead is the impairment of reproductive functions, as manifested by a smaller number of spawning females and in their lower fecundity during spawning.     

Hypoxic conditions induce centrum defects in red sea bream Pagrus major (Temminck and Schlegel)

A previous study elucidated that an extreme hypoxia during somitogenesis induced the most frequent skeletal malformation centrum defects in red sea bream (RSB), Pagrus major. In this study, details of the hypoxic conditions to induce them in RSB, dissolved oxygen (DO) concentration and exposure time to hypoxia, were investigated. Fertilized eggs were exposed to seawater of six DO concentrations (0%, 10%, 25%, 50%, 75% and 100% of saturation) for seven different periods (5, 10, 30, 60, 120, 240 and 360 min) during somitogenesis. Somitic disturbances in newly hatched larvae were induced by exposure to 0% and 10% DO concentration for 10 and 120 min and longer respectively. Rearing eggs exposed to hypoxic condition of 10% DO for 240 min for 40 days post‐hatch showed that the location and the frequency of somitic disturbances in larvae and centrum defects in juveniles were significantly correlated (P<0.01). Dissolved oxygen concentration of the interstitial water in the egg high density layer formed at the water surface in a stationary state abruptly decreased to 3.7% within 7 min. Centrum defect induction by exposure of eggs to extreme low DO concentrations for a short period, which is the probable situation in the practical juvenile production, suggests that careful maintenance of DO concentration is important in the incubating water of fertilized eggs during egg sorting and transportation, where eggs are made into a pile and undergo hypoxia, for the prevention of centrum defects.     

Occurrence of demersal fishes in relation to near‐bottom oxygen levels within the California Current large marine ecosystem

Various ocean‐climate models driven by increased greenhouse gases and higher temperatures predict a decline in oceanic dissolved oxygen (DO) as a result of greater stratification, reduced ventilation below the thermocline, and decreased solubility at higher temperatures. Since spreading of low oxygen waters is underway and predicted to increase, understanding impacts on higher trophic levels is essential. Within the California Current System, shoaling of the oxygen minimum zone (OMZ) is expected to produce complex changes. Onshore movement of the OMZ could lead to habitat compression for species with higher oxygen requirements while allowing expansion of species tolerant of low bottom DO. As part of annual groundfish surveys, we sampled catch across a range of conditions from the upper to the lower limit of the OMZ and shoreward across the continental shelf of the US west coast. DO ranged from 0.02 to 4.25 mL L^?1 with 642 stations (of 1020 sampled) experiencing hypoxic conditions in 2008–2010. Catch and species richness exhibited significant and positive relationships with near‐bottom oxygen concentration. The probability of occurrence was estimated for four species (spotted ratfish, petrale sole, greenstriped rockfish and Dover sole) using a binomial Generalized Additive Model. The models for each species included terms for position, day of the year, salinity, near‐bottom temperature and the interaction term between depth and near‐bottom DO. Spotted ratfish and petrale sole were sensitive to changes in near‐bottom oxygen, while greenstriped rockfish and Dover sole show no changes in probability of occurrence in relation to changes in oxygen concentration.