浙江南部海域银姑鱼的生活史参数估算及资源评价

为了评估银姑鱼资源开发状态，实验根据2016年在浙江南部海域底拖网的调查数据，研究了银姑鱼的生活史参数，并基于单位补充量模型对其资源状态进行评价，进而探讨不同自然死亡系数和捕捞选择性对资源评价结果的影响。结果显示，银姑鱼渐近体长估计值为25.36 cm，生长速率为0.32/年，当前开捕体长(13.52 cm)远小于其初次性成熟体长(17.79 cm)；自然死亡系数估计值为0.74，总死亡系数为2.62，当前捕捞死亡系数为1.88。基于以上参数，构建了单位补充量渔获量YPR模型和单位补充量亲体生物量SSBR模型，随着F的增加，YPR先增大后减小，而SSBR则减少。银姑鱼生物学参考点F_0.1为0.78，F_max为3.43，F_20%为0.66，F_40%为0.33，可知当前捕捞强度远大于防止补充型过度捕捞警戒线F_20%。敏感性分析结果显示，自然死亡系数的不确定性将明显影响单位补充量模型的研究结果和相关生物学参考点的估算值，而不同选择性系数，尤其是开捕体长，也直接影响单位补充量模型的结果。研究表明，当前浙江南部近海银姑鱼种群已处于补充型过度捕捞状态，为维持渔业资源的可持续发展，建议适当减小开发力度，增大开捕体长；为提高资源状态评价的准确性，建议减小自然死亡系数的不确定性。本研究可为银姑鱼资源的养护和管理提供科学建议。     

Growth,diet, and reproduction of Eurasian perch <Emphasis Type="Italic">Perca fluviatilis</Emphasis> L. in Lake Varese,northwestern Italy

No data have previously been reported on Eurasian perch Perca fluviatilis L. in Lake Varese. In this study, the growth, diet, and reproductive biology of the Eurasian perch population were investigated with the aim of providing information that may serve as a basis for efficient resource management. A total of 240 specimens were caught during the monthly sampling campaign from November 2006 through October 2008. The length-to-weight relationships were W _t = 8.4 × 10⁻³ L _t^3.10 (males) and W _t = 4.1 × 10⁻³ L _t^3.36 (females). The parameters for the von Bertalanffy growth function for pooled sexes were L _∞  = 33.17 cm, k = 0.20 year⁻¹, and t ₀ = −1.34 year. Perch in Lake Varese spawn from April through May. Sexual maturity is reached when males are 2 years old, in females mostly when they are 3 years old. Relative fecundity (F _rel) and absolute fecundity (F _abs) were assessed for females. Fecundity values were similar to data reported for other European populations: females of age 2+ F _rel = 102,457 ± 12,275, age 3+ F _rel = 131,767 ± 5,891, and age 4+ F _rel = 131,252 ± 15,555. Perch diet spectrum was wide and somewhat characterized by season. Perch in Lake Varese feed on macroinvertebrates, mainly Chironomidae and Chaoborus, zooplankton, and juvenile rudd Scardinius erythrophthalmus.     

Spatial avoidance of tu‐fish Schizopygopsis younghusbandi for different sounds may inform behavioural deterrence strategies

Water diversions for hydropower and other applications can potentially affect wild fish populations. Although some evidence indicates that acoustic barriers can prevent fish from entrainment into such infrastructures, few studies have been conducted on filtering candidate sound stimuli. Here, the effectiveness of three types of sounds acting as acoustic barriers to prohibit the movement of tu‐fish Schizopygopsis younghusbandi (Regan) was evaluated. The phonotaxic response of the fish to recordings of hissing sound (sound of Chinese alligator Alligator sinensis hissing), outboard motorboat and pile driving noise, compared to control conditions (recordings of ambient riverine noise), was investigated using playback approaches in a fibreglass tank. The tu‐fish reacted to the hissing sound at relatively low sound intensity by exhibiting negative phonotaxis with significantly more responses (F_3,79 = 49.590, p < 0.01) and faster swimming (F_3,219 = 310.086, p < 0.01) away from the sound source during the 10‐min trials than to control conditions. However, the fish were relatively impervious to the outboard motorboat and pile driving noise even when the sound intensities were increased. These results indicate that the potential use of the hissing sound to manipulate fish behaviour and to help protect them from water diversion structures.     

Rebuilding Mediterranean fisheries: a new paradigm for ecological sustainability

In Mediterranean European countries, 85% of the assessed stocks are currently overfished compared to a maximum sustainable yield reference value (MSY) while populations of many commercial species are characterized by truncated size‐ and age‐structures. Rebuilding the size‐ and age‐structure of exploited populations is a management objective that combines single species targets such as MSY with specific goals of the ecosystem approach to fisheries management (EAF), preserving community size‐structure and the ecological role of different species. Here, we show that under the current fishing regime, stock productivity and fleet profitability are generally impaired by a combination of high fishing mortality and inadequate selectivity patterns. For most of the stocks analysed, a simple reduction in the current fishing mortality (F_cur) towards an MSY reference value (F_MSY), without any change in the fishing selectivity, will allow neither stock biomass nor fisheries yield and revenue to be maximized. On the contrary, management targets can be achieved only through a radical change in fisheries selectivity. Shifting the size of first capture towards the size at which fish cohorts achieve their maximum biomass, the so‐called optimal length, would produce on average between two and three times higher economic yields and much higher biomass at sea for the exploited stocks. Moreover, it would contribute to restore marine ecosystem structure and resilience to enhance ecosystem services such as reservoirs of biodiversity and functioning food webs.     

Diphenyl diselenide‐loaded nanocapsules in silver catfish feed enhance growth,improve muscle antioxidant/oxidant status and increase selenium deposition: Advantages of nanotechnology for fish health

The aim of this study was to determine whether feed supplementation with nanoencapsulated Ph₂Se₂ would improve the growth performance of silver catfish and would maintain or improve the muscle antioxidant system. Final mean weight (p = .031), weight gain (p = .014) and specific growth rates (p = .045) were significantly higher in supplemented fish than in the control group. Muscle reactive oxygen species (p = .0001) levels were significantly lower in supplemented fish than in the control group. Also, muscle hydrogen peroxide (p = .0001) and lipid peroxidation (p = .0001) levels were significantly lower in supplemented fish than in the control group. Muscle antioxidant capacity against peroxyl radical (p = .00001) levels were significantly higher in fish supplemented with both Ph₂Se₂ forms (free or nanocapsules) than in the control group, while muscle superoxide dismutase (p = .001) and catalase (p = .0001) activities were significantly higher in supplemented fish than in the control group. Finally, selenium (Se) deposition (p = .00001) was significantly higher in the muscle of fish supplemented with free and nanoencapsulated forms compared with the control; and deposition levels were significantly higher in fish supplemented with Ph₂Se₂‐loaded in nanocapsules compared with the free form. Based on this evidence, Ph₂Se₂‐loaded in nanocapsules improves silver catfish performance and antioxidant/oxidant status. The greater content of Se (1.22 µg/g muscle) in the muscle of fish fed with dietary Ph₂Se₂‐loaded nanocapsules indicates that it may be considered a nutraceutical for fish.     

Age and growth of the largemouth perch Percichthys colhuapiensis in the Negro river, Argentine Patagonia

Largemouth perch (Percichthys colhuapiensis) represents one of the most economically important fish species in the Argentine Patagonia. However, little research has been done on the age and growth and population dynamics of this fish, though both studies are essential to properly deal with fisheries forecasts and management. As a contribution to elaborating management programmes for P. colhuapiensis, we evaluated the age and growth of this species in the Negro river via scale and whole otolith reading methods. The sample consisted of 579 specimens ranging in total length (TL) from 90 to 475 mm, captured seasonally from December 1994 to December 1995. The formation of scale annuli (end of winter) and the hyaline zone on otoliths (winter) of adult fish coincided with the beginning of the spawning season (end of winter-beginning of spring). The maximum estimated age was 11 years, which indicates that this is a relatively long-lived species. Otoliths were useful for ageing specimens 1–5 years-old, but above this age whole otoliths yielded lower age estimates than scales. Isometric growth of weight with length was found for total population, juveniles, and separate sexes (p > 0.25 in all cases). No significant differences between the length–weight relationships of sexes were observed (p > 0.10). Length at first maturity was significantly higher for males (TL₅₀ = 271 mm TL; r = 0.88) than for females (TL₅₀ = 243 mm TL; r = 0.96) (p < 0.01). Largemouth perch exhibited a consistent pattern of increase in length with age, with a period of fast growth during the first 5 years, and a slow-growing phase during the rest of his life. The growth parameters based on scale data were L∞: 462.1 mm, k = 0.23 and t₀ = −0.94 for total population, L∞: 402.3 mm, k = 0.33 and t₀ = −0.67 for males, and L∞: 548.4 mm, k = 0.15 and t₀ = −1.59 for females, whereas those based on otolith reading were L∞: 537.4 mm, k = 0.17 and t₀ = −1.0 for total population, L∞: 497.6 mm, k = 0.21 and t₀ = −0.79 for males, and L∞: 582.0 mm, k = 0.14 and t₀ = −1.53 for females. Scales are concluded to be the best structure to age P. colhuapiensis because they rendered L∞ values closer to the maximum TL observed, high precision, easiness of collection, low processing time, and the possibility of performing non-destructive monitoring studies.     

Mangroves enhance local fisheries catches: a global meta‐analysis

Mangroves are among the most productive ecosystems in tropical and subtropical regions. Historically, mangroves are assumed to support artisanal fisheries, leading decision‐makers to protect mangroves based on this premise. However, this relationship remains unclear, despite positive correlations obtained in different geographical regions. Here, we provide the first meta‐analysis of the mangroves–fisheries linkage at a global level. After conducting a systematic review, 23 publications containing 51 studies estimating the mangrove–fishery linkage were obtained. A random effect model was used to estimate the effect size (Pearson's correlation coefficient) of each individual study as well as the overall effect size. We found strong evidence for the mangrove–fishery linkage with an overall effect size of r = 0.72 (95% CI: 0.61–0.81), and substantial heterogeneity was observed (Q = 143.88, df = 50, P < 0.01). The countries where the studies were carried out were the only significant moderator (Q_M = 26.07, P < 0.01), while fisheries types (i.e. crab, fish, shellfish, prawn and total) and global regions were not good predictors of the relationship. Our results show that mangrove area is a good predictor of fishery catches overall, confirming the importance of conserving such habitats.     

Age and growth of two gizzard shads, <Emphasis Type="Italic">Nematalosa come</Emphasis> and <Emphasis Type="Italic">N. japonica</Emphasis>, in coastal waters around Okinawa Island,southwestern Japan

The age and growth of two Nematalosa species around Okinawa Island were examined using sectioned otoliths collected from September 2003 to April 2006. Monthly changes in the frequency of the appearance of a translucent band on the outer margin of the otoliths indicated that ring formation occurred once a year from January to July for Nematalosa come and from January to March for Nematalosa japonica. The von Bertalanffy growth equations for both species were as follows: N. come: L _t  = 365.5{1 − exp[−0.111 × (t + 0.288)]} for females and L _t  = 214.7{1 − exp[−0.700 × (t – 1.110)]} for males; N. japonica: L _t  = 205.1{1 − exp[−1.068 × (t − 1.180)]} for females and L _t  = 195.5 {1 − exp[−1.293 × (t − 1.269)]} for males. The maximum ages observed for N. come and N. japonica were 11 and 6 years old, respectively. The growth of these species was characterized by the slow growth of N. come over many years, resulting in a larger size than N. japonica.     

Effect of short‐term fasting and re‐feeding on growth,digestive enzyme activities and antioxidant defence in yellowfin seabream,Acanthopagrus latus (Houttuyn, 1782)

An 80‐day feeding trial was conducted to evaluate the influence of different short‐term fasting and re‐feeding strategies on growth and physiological responses in yellowfin seabream, Acanthopagrus latus (2.4 ± 0.2 g) fingerlings. The fish were subjected to four different feeding regimes, and the control group fed four times daily to apparent satiation throughout the whole feeding period, while the other three groups were deprived for 2, 4 and 8 days followed by 8, 16 or 32 days of re‐feeding (F₂R₈, F₄R₁₆ and F₈R₃₂, respectively) in repeated cycles for 80 days. The fish in the control and F₂R₈ groups had the highest and the lowest total length, respectively (p < .05). Moreover, fish exposed to F₄R₁₆ had the highest hepatosomatic indices, while control fish had the lowest hepatosomatic indices (p < .05). Fish in the F₂R₈ group relatively had higher catalase and glutathione‐S‐transferase activities than other groups (p < .05). Furthermore, total protease, α‐amylase and alkaline phosphatase activities in the F₄R₁₆ and F₈R₃₂ were higher than the F₂R₄ and control groups (p < .05). Overall, this study showed that compensatory growth in weight and length and digestive enzyme activities were observed in the F₄R₁₆ and F₈R₃₂; however, the increase in the activity of antioxidant enzymes in the F₈R₃₂ group indicated that oxidative stress remained after 80 days of re‐feeding in the liver.     

Identifying spawner biomass per‐recruit reference points from life‐history parameters

Analysis of spawning biomass per‐recruit has been widely adopted in fisheries management. Fishing mortality expressed as spawning potential ratio (SPR) often requires a reference point as an appropriate proxy for the fishing mortality that supports a maximum sustainable yield—F_MSY. To date, a single generic level between F_30% and F_40% is routinely used. Using records from stock assessments in the RAM Legacy Database (RAMLD), we confirm that SPR at MSY (SPR_MSY) is a declining function of stock productivity quantified by F_MSY. We then use general linear models (GLM) and Bayesian errors‐in‐variables models (BEIVM) to show that SPR_MSY can be predicted from life‐history parameters (LHPs, including maximum lifespan, age‐ and length‐at‐maturation, growth parameters, natural mortality, and taxonomic Class) as well as gear selectivity. The calculated SPR_MSY ranges from about 13% to 95% with a mean of 47%. About 64% of the stocks in the RAMLD require SPR_MSY > 40%. Modelling SPR_MSY reveals that LHPs plus Class explain 61% of the deviance in SPR_MSY. Faster‐growing, low‐survival, and short‐lived species generally require a high SPR. With equal LHPs, elasmobranchs require about 20% higher SPR_MSY than teleosts. When F_MSY is estimated from fisheries that harvest older fish, increasing the vulnerable age by one year leads to about an 8% increase in SPR_MSY. The BEIVM yields smaller variance and bias than the GLM. The models developed in this study could be used to predict SPR_MSY reference points for new stocks using the same LHPs for calculating F_x%, but without knowledge of the stock‐recruitment parameters.     

Population dynamics and fishery benefits of a large legal size of a pelagic sportfish,the Talang queenfish,Scomberoides commersonnianus,in northern Australia

The life history of an increasingly important pelagic commercial and sport fish, the Talang queenfish, Scomberoides commersonnianus, was studied in northern Australia to investigate the stock status and assess current management of the species using minimum legal lengths (MLL). Estimated von Bertalanffy growth parameters were L_∞ = 1404 mm FL, K = 0.10 year⁻¹ and t₀ = −1.21 year⁻¹. There was no significant difference in growth between sexes. Ages ranged from 1 to 11 years with age composition differing between the commercial (mainly 6–7 years) and sport fishery (mainly 2–4 years). Females matured (L₅₀) at 635 mm FL and 4–5 years. Spawning occurred between August and March when mature females were estimated to produce 259,488–2,859,935 eggs per spawning. Natural mortality (M) was estimated as 0.16–0.26 year⁻¹, while the combined fishing mortality (F_current) from commercial and sport fisheries was 0.38–0.48 year⁻¹. Yield-per-recruit analyses revealed that under current MLL limits (no MLL or 45 cm TL) and natural mortality (M = 0.16, 0.2 and 0.26 year⁻¹), F_current exceeded the reference points F_max (0.15–0.22 year⁻¹) and F_0.1 (0.10–0.15 year⁻¹), suggesting the stock may be growth overfished if the current situation remains unchanged. Although a stock–recruitment relationship is unknown, spawning stock biomass-per-recruit analysis indicates the stock may also be recruitment overfished since F_current exceeded the reference points F_25% (0.19–0.24 year⁻¹) and F_40% (0.11–0.15 year⁻¹). Increasing the MLL corresponding to L₅₀ of females (70 cm TL) will greatly improve the yield and long-term sustainability of the stock, and also enhance the sport fishery by increasing the number of larger trophy fish.     

Effect of temperature on the development of eggs and the daily pattern of spawning of round herring <Emphasis Type="Italic">Etrumeus teres</Emphasis>

Effect of temperature on the development of eggs of round herring Etrumeus teres was experimentally examined to construct a temperature-dependent egg development model. Mature fish were collected in the field and their eggs were artificially fertilized onboard. The eggs were incubated at nine temperatures set between 14.0 and 25.0°C. All eggs at the lowest three temperatures, 14.0°C, 15.0°C, and 16.0°C, ceased development and died at various stages before hatching. Durations required to hatching after fertilization ranged from 38.0 h at 25.0°C to 90.0 h at 17.5°C. The temperature-dependent egg development model, i.e., egg age in hours (y _i,t ) at the ith stage and temperature t (°C), was expressed as: y _i,t  = 4.604 × exp(−0.100 × t −0.129 × i) × i ^2.593. From the application of the model to early-stage eggs collected in the field, it is concluded that round herring starts spawning immediately after sunset and almost completes spawning by midnight. The temperature-dependent egg development model and the daily pattern of spawning presented in this study are essential tools for developing the daily egg production method to estimate the spawning stock biomass.     

Age and growth of the lizardfish <Emphasis Type="Italic">Saurida elongata</Emphasis> from the Tsushima/Korea Strait

We studied the age and growth of the lizardfish Saurida elongata using ground thin sections of otoliths (sagittae) from specimens collected in the Tsushima/Korea Strait between May 1999 and June 2001. A total of 695 individuals with fork lengths (FL) ranging from 189 to 478 mm were examined. The frequency of translucent zone occurrence at the outer margin of the otoliths indicated that translucent zones formed once a year between November and February. Most of the males examined were estimated to be 2–7 years old and the females, 3–9 years old. The maximum estimated age of a male specimen was 10 years and that of a female, 11 years. The estimated von Bertalanffy growth curves were FL _t  = 451{1 − exp[−0.172(t + 2.50)]} and FL _t  = 515{1 − exp[−0.151(t + 2.47)]} for males and females, respectively. At all ages, the FL at a specific age for females was greater than that for males, suggesting that females of this species grow faster than males.     

Stable isotopes infer the value of Australia’s coastal vegetated ecosystems from fisheries

Wild capture fisheries provide substantial input to the global economy through employment and revenue. The coastal zone is especially productive, accounting for just 7% of the total area of the ocean, but supporting an estimated 50% of the world's fisheries. Vegetated coastal ecosystems—seagrass meadows, tidal marshes and mangrove forests—are widely cited as providing nutritional input that underpin coastal fisheries production; however, quantitative evidence of this relationship is scarce. Using Australia as a case study, we synthesized fisheries stable isotope data to estimate nutritional input derived from coastal vegetated ecosystems and combined these “proportional contribution” estimates with total annual catch data from commercial fisheries to determine species‐specific dollar values for coastal vegetated ecosystems. Based on the data from 96 commercially important fish species across Australian states (total landings 14 × 10⁶ tonnes pa), we provide a conservative estimate that Australia's coastal vegetated ecosystems contribute at least 78 million AUD per year to the fisheries economy. Two thirds of this contribution came from tidal marshes and seagrasses that were both equally valued at 31.5 million AUD per year (39.4%) followed by mangroves at 14.9 million AUD per year (18.6%). The highest dollar values of coastal ecosystems originated from eastern king prawn (Melicertus plebejus) and giant mud crab (Scylla serrata). This study demonstrates the substantial economic value supported by Australia's coastal vegetated ecosystems through commercial fisheries harvest. These estimates create further impetus to conserve and restore coastal wetlands and maintain their support of coastal fisheries into the future.     

Econometric model of viability/profitability of octopus (<Emphasis Type="Italic">Octopus vulgaris</Emphasis>) ongrowing in sea cages

The interest in diversifying aquacultural production with new species is evident, preferably with species with a high commercial value and whose consumption is not geographically limited. In this sense, octopus would be a good choice. The present work, therefore, presents an economic-financial analysis of the commercial viability of octopus ongrowing in the Mediterranean, paying special attention to the one- or two-cycle approach. Viability–profitability equations are developed for analysing economic parameters associated with production. To estimate the investment, an offshore ongrowing installation was designed comprising 150 cages containing 30,000 individuals. Growth was estimated for the two strategies: (A) Two consecutive cycles per year (2CY), each lasting 3.5 months from October to June. Initial weight was 0.7 kg, and the mean final weight was 2.7 kg. (B) One growth cycle per year (1CY) beginning in November or December and finishing in April or May, starting with the same weight individuals (0.7 kg) and giving individuals with a final weight of 3.65 kg. The highest costs, the most important from an economic point of view, are feed (38.57 and 40.03%, respectively), fixed assets (25.26 and 17.47%, respectively), juveniles (16.65 and 23.02%, respectively), and in fourth place salaries (14.34 and 15.60%, respectively). The equations obtained for the variables NPV (Net Present Value) and IRR (Internal Ratio of Return) are the following: 1 cycle per year (1CY), NPV = −489,088 − 1.45 K − 1,439,823 C _F − 1,477,890 C _J − 1,460,627 C _O + 1,432,386 SP, IRR = 0.1328 − 7.82 × 10⁻⁸ K − 0.0416 C _F − 0.0437 C _J − 0.0427 C _O + 0.0412 SP. 2 cycles per year (2CY), NPV = −404,431 − 1.46 K − 2,118,410 C _F − 2,121,221 C _J − 2,144,755 C _O + 2,129,223 SP, and IRR = 0.0952 − 6.95 × 10⁻⁸ K − 0.0586 C _F − 0.0588 C _J − 0.0588 C _O + 0.0613 SP. The NPV and IRR values estimated with the econometric equations for each option using the initial variables confirm that 1CY has a higher NPV (3,013,569 €) and IRR (12.27%) than 2CY, with an NPV of 2,396,708 € and IRR of 10.39%. In both cases, octopus ongrowing is economically viable, although 1CY is the most favourable system.     

Fisheries resource management of the daggertooth pike conger,Muraenesox cinereus,using existing limited datasets in the western Seto Inland Sea,Japan

The daggertooth pike conger, Muraenesox cinereus (Forsskål), has become an important fish resource in the western Seto Inland Sea, Japan, since the 1990s. However, introducing sustainable fisheries resource management for this species is difficult in this region because stock assessments have not been performed, and official fisheries statistics for this stock were discontinued after 2007. This study used existing limited data sets to compile the first report for fisheries resource management for this M. cinereus stock. Yield‐per‐recruit analyses showed that increasing fishing pressure above current levels would provide only a minimal increase in expected catch levels. Hence, the current harvest level is considered to represent the upper limit of fishing pressure. Age composition in a given year could potentially be used to forecast landing abundance for the following 2 years. This study provides a basis for establishing effective fisheries resource management strategies for M. cinereus.     

Movement patterns and growth estimates of big skate (Raja binoculata) based on tag-recapture data

From 2003 through 2006, 18,180 big skate (Raja binoculata) were tagged in three regions in British Columbia, Canada: northern Hecate Strait, Queen Charlotte Sound and the west coast of Vancouver Island. To date, this is the largest tagging program conducted for skates or rays worldwide. As of December 31, 2008, 7% of the tagged fish (n = 1238) have been recaptured through the commercial fisheries. Generally, 75% of the recaptured fish were recaptured within 21 km of the tagging location. Long-range movements (up to 2340 km) were undertaken by a small percentage (1.5%) of the recaptured fish. Tagged big skate were recaptured in waters off of Oregon, Washington, throughout the Gulf of Alaska and the Bering Sea. The majority of big skate recaptured outside of Canadian waters were female (83%, n = 15), of which 80% (n = 12) were likely immature at release. Three methods of estimating growth parameters were employed and produced varying results. The Gulland and Holt method was not able to produce growth parameter estimates. The GROTAG method for combined sexes produced von Bertalanffy growth curve parameters L_∞ (294.7 cm), K (0.05) and t₀ (?1.44) that were similar to published estimates for British Columbia big skates. The von Bertalanffy growth curve parameters produced by Fabens method for combined sexes were L_∞ = 168.6 cm, K = 0.16 and t₀ = ?0.81.     

Reproductive ability of second generation ornamental (koi) carp (Cyprinus carpio L.) × goldfish (Carassius auratus L.) hybrids and characteristics of their offspring

The purpose of this study was to investigate the reproductive ability of second generation (F₂) koi (Cyprinus carpio L.) × goldfish (Carassius auratus L.) hybrids. Only diploid F₂ males and females were fertile and used in crosses. A significant increase was recorded in male fertility in F₂ versus F₁. In contrast with an earlier study in which only one fertile F₁ male was found, about 20% of F₂ males produced sperm. The observed reproductive ability of F₂ hybrids was similar to that demonstrated by the only fertile F₁ male and F₁ females. F₂ males produced diploid spermatozoa and generated triploids when crossed with koi females. All triploid fish in these progenies were males indicating that F₂ males had a sex chromosome constitution of XY. F₂ females produced diploid eggs and generated mostly triploids when crossed with koi males. In progenies obtained by crosses of F₂ males with F₁ and F₂ females, most of the surviving juveniles (63%–100%) were diploid; a minority of juveniles were aneuploid (ploidy ranged from 2.1n to 3.6n). Diploid fish in these progenies were presumably the result of spontaneous androgenesis and gynogenesis, by the same mechanisms observed earlier in progenies obtained by crossing the F₁ male with F₁ females.     

Carrying capacity for finfish aquaculture. Part I—Near-field semi-analytic solutions

The ecosystem carrying capacity for aquaculture cage farming in South Australia is based on guidelines that the maximum feed rates (and farmed fish biomass) be determined such that the concentration c of a given dissolved nutrient does not exceed a prescribed value (say c_P). The problem then is one of relating the nutrient flux F, due to feeding, to the tracer concentration c. To this end the evolution of concentration is modelled using the depth-averaged advection–diffusion equation for a constant source flux F over a finite area cage (or lease) and for both constant and time dependent (tidal) velocities. The divergence theorem is applied to this equation to obtain a new scale estimate of the relation between the flux F and the maximum concentration c_max of a nutrient in the cage region: c_max ≈ F·T*, where T* is a time scale of cage “flushing” that involves both advection and diffusion. The maximum allowed nutrient flux F (and carrying capacity of fish biomass) can then be simply estimated from: F ≈ c_P/T*. New semi-analytic solutions of the advection–diffusion equation for a finite (cage) source are then derived to explore the physics of concentration evolution for constant and tidally varying currents, and to show that the estimate c_max ≈ F·T* is surprisingly robust and generally within 40% of the exact values for a wide set of advective/diffusive parameters. The results generally should find application in other finite source flux problems in the coastal oceans including desalination plants and waste water outfalls.     

Growth,sex ratio,and maturation rate with age in the blackspot tuskfish <Emphasis Type="Italic">Choerodon schoenleinii</Emphasis> in waters off Okinawa Island,southwestern Japan

The growth, sex ratio with age, and age at sexual maturation were determined based on sectioned otoliths in 257 specimens of the blackspot tuskfish Choerodon schoenleinii collected in waters off Ryukyu Island. Opaque rings observed by reflected light in the sectioned otoliths were found to form once a year from January to July. The three growth parameters of the von Bertalanffy growth equation were L_∞ = 68.1 (cm), k = 0.263, and t ₀ = −0.023 (year). The age at which the sex ratio reached 50% by sexual transition was about 6.15 years, and the age at which 50% of females were sexually mature was approximately 2 years. The oldest specimen among the samples was 17 years old.