Age, growth and mortality of greater amberjack from the southeastern United States

Rings on 323 sectioned otoliths (sagittae) were used to determine the ages of greater amberjack, Seriola dumerili, sampled from headboats and commercial handline vessels operating out of ports from North Carolina through the Florida Keys. Age and growth determinations were difficult. Rings were identified and counted on 71% of the samples, but measurements could be made on only 48%. The oldest fish examined was 17 years old and was 1552 mm total length (TL). Back-calculated mean lengths at annulus formation were 366, 873, 1207 and 1471 mm TL for ages 1, 5, 10 and 15, respectively. The von Bertalanffy equation describing theoretical growth for TL was L_t = 1648(1 − e^{−0.119(t + 1.230)}), where T = years. The equation using fork lengths (FL) was L_t = 1514(1 − e^{−0.115(t + 1.178)}). The weight-length relationship for greater amberjack was W = 7.2 × 10⁻⁸L^2.700, where W is the whole fish weight (in kg), and L is the total length (in mm). Conversion of total length to fork length may be obtained using the equation: FL = −4.807 + 0.887(TL), and fork length to total length: TL = 20.110 + 1.111(FL). Greater amberjack are fully recruited to the fishery by age 8. Estimates of total instantaneous mortality (Z) ranged from 0.60 to 0.65 depending on the year.     

Hydroacoustic in situ target strength of smelt (Osmerus eperlanus (L.))

Dependence of the in situ acoustic target strength (TS) of smelt (Osmerus eperlanus (L.)) on the total fish length (L) was estimated from TS measurements made with a split-beam 120 kHz echo sounder with reference to fish length–frequency distributions in trawl catches. The studies were conducted in the eutrophic and turbid Lake Hiidenvesi in southern Finland. Smelt dominated the catches-in-number with proportions at different sampling stations ranging from 91.8 to 100%. A TS–length equation of the form TS = alog L − b was fitted through the modes in the TS-distributions and in the respective fish length distributions. The estimated model (±parameter standard error) was TS = 23.4 (±2.24)log₁₀ L − 68.7 (±1.82). With a pre-defined slope of 20, the fitted equation was TS = 20 log₁₀ L − 65.9 (±0.23). The estimated day–night difference in TS–length relationship was not significant (t-test, p = 0.37).     

Age, growth, and reproduction of silky sharks, Carcharhinus falciformis, in northeastern Taiwan waters

To examine the age, growth and reproduction of silky sharks, Carcharhinus falciformis, in the waters off northeastern Taiwan, 469 specimens (213 females and 256 males) were collected from August 2000 to January 2002 at the Nanfanao fish market, northeastern Taiwan. The relationship between body weight (W) and total length (TL) for both sexes combined was expressed as: W = 2.92 × 10⁻⁶ TL^3.15 (n = 469, p < 0.01). The relationship between TL and vertebral centrum radius (R) for both sexes combined data was estimated as: TL = 25.979 + 18.197R (n = 250, p < 0.01). Growth bands (including translucent and opaque zones) in precaudal vertebrae formed once a year between December and January and were counted up to 11 and 14 for females and males, respectively. The von Bertalanffy growth function (VBGF) was used to model the observed length at age data. The sexes combined VBGF predicted an asymptotic length (L_∞) = 332.0 cm TL, growth coefficient (k) = 0.0838 year⁻¹, age at zero length (t₀) = −2.761 year (n = 250, p < 0.01). Size at 50% maturity for males was estimated to be 212.5 cm based on the logistic curve, which corresponded to 9.3 years. Females matured at 210–220 cm, which correspond to 9.2–10.2 years. The length at birth was estimated to be 63.5–75.5 cm TL. The number of embryos per litter was 8–10 and sex ratio of embryos was 1:1.     

Regional size, age and growth differences of red grouper (Epinephelus morio) along the west coast of Florida

Red grouper (Epinephelus morio) were collected from the west coast of Florida, the central area of fishery harvest in U.S. waters, by fishery-dependent sources during 2000–2005. The west Florida shelf was divided into two regions: north (capture locations ≥28°N latitude) and south (capture locations <28°N latitude). Significant differences were found for age, length, and size-at-age by region and by gear; red grouper from the north were significantly younger and smaller on average than those from the south. Regional differences were also noted with respect to age progression; year class trends were only detected in the north. The 1996 year class dominated the landings in 2000–2001 (ages 4 and 5) and the 1999 year class dominated in 2004–2005 (ages 5 and 6). Regional data were fit to a size-modified von Bertalanffy growth model indicating smaller asymptotic length (L_∞) and faster growth rate (k) in the north (north: L_∞ = 800 mm, k = 0.23 mm year⁻¹, t₀ = 1.12; south: L_∞ = 863 mm, k = 0.15 mm year⁻¹, t₀ = 0.05). Mortality estimates derived from catch curves resulted in higher total and fishing mortality in the north for both gears. Alternative explanations of regional differences likely depend on nursery delineation and correlation to periodic environmental events such as red tides and hurricanes; all possibly important factors based upon anecdotal information. Nevertheless, our finding of regional demographic differences in red grouper from the west coast of Florida suggests a more complex population spatial structure for red grouper.     

Modeling industry-wide sediment oxygen demand and estimation of the contribution of sediment to total respiration in commercial channel catfish ponds

Data collected from 45 commercial channel catfish, Ictalurus punctatus, ponds were used to develop empirical models predicting sediment oxygen demand (SOD). Seven acceptable models were combined with a Monte-Carlo sampling distribution to predict industry-wide sediment oxygen demand (SOD_i). The SOD_i values obtained from the best equation were used in simulations to assess the effect of diurnally varying water column dissolved oxygen (DO) concentrations on SOD and the effect of pond water depth on the contribution of SOD to overall pond respiration. Estimated SOD_i ranged from 62 to 962 mg m⁻² h⁻¹, with a mean of 478 mg m⁻² h⁻¹. There was a 95% probability of mean SOD_i being ≥700 mg m⁻² h⁻¹. The effects of diurnal variation in DO concentration in the water column on expression of SOD was modeled by combining maximum SOD_i, an empirical relationship between DO and SOD, and simulated pond DO concentrations. At DO concentrations >15 mg l⁻¹, diel SOD in catfish ponds exceeded 20 g O₂ m⁻² day⁻¹. But when average diel DO was <4 mg l⁻¹ and the range of DO concentration was 6–8 mg l⁻¹, SOD decreased to 13 g O₂ m⁻² day⁻¹ because DO availability limited the full expression of potential SOD. Respiration totals for sediment (average SOD_i), plankton, and fish respiration were calculated for pond water depths ranging from 0.25 to 4 m. Although whole-pond respiration increases as pond depth increases, the proportion of total respiration represented by sediment decreased from 48 to 10% by increasing water depth over this range. The results of these studies show that SOD is a major component of total pond respiration and that certain management practices can affect the impact of SOD on pond oxygen budgets. Mixing ponds during daylight hours, either mechanically or by orienting ponds for maximum wind fetch, will increase oxygen supply to sediments, thereby allowing maximum expression of SOD and maximum mineralization of sediment organic matter. Given a mixed condition caused by wind or other artificial means, the construction of deeper ponds increases the total mass of DO available for all respiration, causing nighttime DO concentrations to decline at a slower rate, reducing the need for supplemental aeration. Because a pond’s water volume decreases over time from sediment accumulation, annual aeration costs will increase with pond age. Constructing ponds with greater initial depth will therefore reduce long-term cost of aeration, allow more flexible management of pond water budget, and reduce the long-term expense associated with pond reconstruction.     

Growth and mortality of the catfish, Hemisynodontis membranaceus (Geoffroy St. Hilaire), in the northern arm of Lake Volta, Ghana

Estimates of growth and mortality of the catfish, Hemisynodontis membranaceus (Geoffroy St. Hilaire), in Lake Volta were obtained from length composition data compiled in 1995 and 1996. The von Bertalanffy growth function (VBGF) estimates were: L _∞=44.5 cm standard length; K= 0.62 year⁻¹; and t ₀=−0.23 years. Natural mortality rate, M , was 1.20 year⁻¹. Total mortality rate, Z , was computed as 4.39 year⁻¹ and the exploitation ratio ( E = F / Z ) was 0.72. Although the fish is estimated to have longevity of about 5 years, those exploited are normally less than 2 years of age, which is indicative of growth over-fishing. In order to arrest over-exploitation of the species, there is a need to establish 'lake reserves'. In addition, the fisheries management should be devolved from the state to the local level to compel fishermen to take greater responsibility for the sustainability and conservation of the fisheries.     

Dopamine modulates the physiological response of the tiger shrimp Penaeus monodon

Levels of glucose, lactate, pO₂, pCO₂, HCO₃⁻, TCO₂, Na⁺, K⁺, Cl⁻, protein, and oxyhemocyanin in the hemolymph and its osmolality and pH were measured when tiger shrimp, Penaeus monodon (13.5 ± 1.5 g body weight), were individually injected with saline or dopamine at 10^− 8, 10^− 7, or 10^− 6 mol shrimp^− 1. Results showed that hemolymph glucose, lactate, pCO₂, HCO₃⁻, and TCO₂ values increased from 2 to 4 h; hemolymph osmolality, Na⁺, and total protein had increased at 2 h; and hemolymph K⁺ decreased from 2 to 8 h after the dopamine injection. All physiological parameters returned to the control values 4–16 h after receiving dopamine. The dopamine injection also significantly decreased the oxyhemocyanin/protein ratio of P. monodon which occurred at 2 h, resulting from an elevation of hemolymph protein and a slight decrease of oxyhemocyanin. These results suggest that stress-inducing dopamine caused a transient period of modulation of energy metabolism, osmoregulation, respiration, and the acid–base balance in P. monodon in adapting to this environmental stress.     

Effects of body weight, water temperature and ration size on ammonia excretion by the areolated grouper (Epinephelus areolatus) and mangrove snapper (Lutjanus argentimaculatus)

The effects of body weight, water temperature and ration size on ammonia excretion rates of the areolated grouper Epinephelus areolatus and the mangrove snapper Lutjanus argentimaculatus were investigated. Under given experimental conditions, L. argentimaculatus had a higher weight-specific ammonia excretion rate than E. areolatus. Weight-specific ammonia excretion rates of fasted individuals of both species showed an inverse relationship with body weight (W, g wet wt.), but a positive relationship with water temperature (t, °C). The relationships for total ammonia nitrogen (TAN) were: E. areolatus: TAN (mg N kg⁻¹ d⁻¹)=21.4·exp^0.11t·W^−0.43 (r²=0.919, n=60); L. argentimaculatus: TAN (mg N kg⁻¹ d⁻¹)=121.5·exp^0.12t·W^−0.55 (r²=0.931, n=60). Following feeding, the weight-specific ammonia excretion rate of E. areolatus increased, peaked at 2 to 12 h (depending on temperature), and returned to pre-feeding levels within 24 h. A similar pattern was observed for L. argentimaculatus, with a peak of TAN excretion being found 6 to 12 h after feeding. Stepwise multiple regression analysis indicated that weight-specific TAN excretion rates of both species increased with increasing temperature and ration (R, percent body wt. d⁻¹): E. areolatus: TAN (mg N kg⁻¹ d⁻¹)=22.8·t−28.8·R−378.2 (r²=0.832, n=24); L. argentimaculatus: TAN (mg N kg⁻¹ d⁻¹)=22.9·t−25.4·R−216.4 (r²=0.611, n=24). The effect of body weight on weight-specific postprandial TAN excretion was not significant in either species (p>0.05). This study provides empirical data for estimating ammonia excretion of these two species under varying conditions. This has application for culture management.     

Substitution of Chaetoceros muelleri by Spirulina platensis meal in diets for Litopenaeus schmitti larvae

The nutritional response of Litopenaeus schmitti larvae to substitution of Chaetoceros muelleri by Spirulina platensis meal (SPM) was evaluated. The substitution levels (S) were 0%, 25%, 50%, 75% and 100%, dry weight basis. Final larval length (FL) ranged from 1.98 to 3.16 mm for the different substitution levels. There was a significant relationship between S and FL, described by the following quadratic equation: FL = 2.853 + 0.01598S − 0.000233S². The substitution level (S) yielding maximum FL was 34.2%. Development index (DI) values ranged from 2.84 to 3.93 and were dependent on substitution level. The corresponding equation was DI = 3.799 + 0.00945S − 0.000189S² (P < 0.01). Maximum DI was obtained at 25.0% substitution. Survival was high (82–87%) and no significant differences were found between treatments. Protein digestibility of either microalgae was high, with 92% for SPM and 94% for C. muelleri, with no significant differences between them. The results in this study indicate that an adequate balance of nutrients in relation to the requirements of the species is critical. To simultaneously improve FL and DI, a 30% substitution of C. muelleri by SPM is suggested. This is equivalent to feeding 0.15 mg larvae^− 1 day^− 1 dry weight basis of a 70% C. muelleri/30% SPM diet, representing 0.078 mg protein larvae^− 1 day^− 1, 0.026 mg lipids larvae^− 1 day^− 1 and 2.732 J larvae^− 1 day^− 1.     

Metabolic scope, swimming performance and the effects of hypoxia in the mulloway, Argyrosomus japonicus (Pisces: Sciaenidae)

The culture of the mulloway (Argyrosomus japonicus), like many other Sciaenidae fishes, is rapidly growing. However there is no information on their metabolic physiology. In this study, the effects of various hypoxia levels on the swimming performance and metabolic scope of juvenile mulloway (0.34 ± 0.01 kg, mean ± SE, n = 30) was investigated (water temperature = 22 °C). In normoxic conditions (dissolved oxygen = 6.85 mg l^− 1), mulloway oxygen consumption rate (M·o₂) increased exponentially with swimming speed to a maximum velocity (U_crit) of 1.7 ± < 0.1 body lengths s^− 1 (BL s^− 1) (n = 6). Mulloway standard metabolic rate (SMR) was typical for non-tuna fishes (73 ± 8 mg kg^− 1 h^− 1) and they had a moderate scope for aerobic metabolism (5 times the SMR). Mulloway minimum gross cost of transport (GCOT_min, 0.14 ± 0.01 mg kg^− 1 m^− 1) and optimum swimming velocity (U_opt, 1.3 ± 0.2 BL s^− 1) were comparable to many other body and caudal fin swimming fish species. Energy expenditure was minimum when swimming between 0.3 and 0.5 BL s^− 1. The critical dissolved oxygen level was 1.80 mg l^− 1 for mulloway swimming at 0.9 BL s^− 1. This reveals that mulloway are well adapted to hypoxia, which is probably adaptive from their natural early life history within estuaries. In all levels of hypoxia (75% saturation = 5.23, 50% = 3.64, and 25% = 1 .86 mg l^− 1), M·o₂ increased linearly with swimming speed and active metabolic rate (AMR) was reduced (218 ± 17, 202 ± 14 and 175 ± 10 mg kg^− 1 h^− 1 for 75%, 50% and 25% saturation respectively). However, U_crit was only reduced at 50% and 25% saturation (1.4 ± < 0.1 and 1.4 ± < 0.1 BL s^− 1 respectively). This demonstrates that although the metabolic capacity of mulloway is reduced in mild hypoxia (75% saturation) they are able to compensate to maintain swimming performance. GCOT_min (0.09 ± 0.01 mg kg^− 1 m^− 1) and U_opt (0.8 ± 0.1 BL s^− 1) were significantly reduced at 25% dissolved oxygen saturation. As mulloway metabolic scope was significantly reduced at all hypoxia levels, it suggests that even mild hypoxia may reduce growth productivity.     

Relationship between Secchi disk visibility and chlorophyll a in aquaculture ponds

The potential of using Bannister's linear equation (k_t=k_w+k_cc) (where k_t is the overall light extinction coefficient, k_w represents the non-phytoplankton light extinction, k_c is the specific light extinction coefficient due to chlorophyll a (chla), c is the chla concentration, and k_cc represents the light extinction due to chla) to partition sources of turbidity in Secchi disk visibility (SDV) measurements in aquaculture ponds was evaluated. Eight data sets from five sites around the world were used in the study. Chlorophyll a data were regressed against the overall light extinction coefficient determined from SDV measurements. The relationship between chla and overall light extinction coefficient was linear for seven of the eight data sets. The contribution of non-phytoplankton turbidity to SDV measurements was estimated by the intercept of the linear regression line (equivalent to k_w). The values obtained (range=3.61–8.91 m⁻¹) were variable and unpredictable between replicate ponds at all sites, but did not vary significantly over time (P<0.05). Because chla concentration serves as an indicator of phytoplankton concentration, the contribution of phytoplankton turbidity to SDV measurements was estimated by the slope of the linear regression line (equivalent to k_c) multiplied by the chla concentration. The slope of the regression line (0.014±0.006 m⁻¹ (mg m⁻³) ⁻¹) was similar to values reported for natural freshwater systems. The partitioned light extinction coefficients and chla concentrations were also used to determine the threshold chla concentration above which SDV measurements are determined primarily by chla. The threshold chla concentrations (177–980 mg m⁻³) above which phytoplankton biomass becomes the primary determinant of SDV were higher than observed chla concentrations. The results indicate that Bannister's linear equation can generally be used to partition and quantify the sources of turbidity in aquaculture ponds. The results also suggest that the contribution of non-phytoplankton turbidity to SDV measurements in fertilized and fed aquaculture ponds can be more important than phytoplankton turbidity.     

Furunculosis in Atlantic salmon (Salmo salar L.) is not readily controllable by bacteriophage therapy

The potential of bacteriophage therapy to control bacterial disease in farmed fish was tested using, as an example, furunculosis of Atlantic salmon, caused by Aeromonas salmonicida subsp. salmonicida.

In vivo testing with Atlantic salmon and rainbow trout (Oncorhynchus mykiss Walbaum) showed no adverse effects, with bacteriophage generally cleared within 96 h of administration by either intraperitoneal (i.p.) injection or oral in-feed.

Juvenile Atlantic salmon were administered a combination of bacteriophage O, R and B (1.9 × 10⁸ pfu fish^− 1) by i.p. injection, after they had been challenged with A. salmonicida subsp. salmonicida 78027, also by i.p. injection. The fish that were injected with bacteriophage immediately after challenge died at a significantly slower rate then those that were either not treated with bacteriophage, or treated 24 h post-challenge. However, the end result (100% mortality) was not affected.

In further experiments the effects of oral (1.88 × 10⁵ pfu g^− 1 fish^− 1 daily for 30 days), bath (1.04 × 10⁵ ml^− 1 daily for 30 days) and i.p. (6.25 × 10⁷ pfu fish^− 1) phage treatment to control furunculosis in experimentally infected Atlantic salmon were compared with antibiotherapy (treatment with 10 mg kg^− 1 bw^− 1 day^− 1 oxolinic acid for 10 days), using an indirect cohabitation challenge. No protection was offered by any of the bacteriophage treatments, compared to the positive challenge group, although significant protection was offered by the oxolinic acid treatment. Analysis of samples taken from the trials demonstrated that bacteriophage were correctly administered to the fish and, on occasion, were isolated from fish that had succumbed to furunculosis. It was also shown that bacteriophage resistant A. salmonicida subsp. salmonicida isolates could be recovered from mortalities in all the treatment groups.

The results suggest that, although there were no safety problems associated with the approach, furunculosis in Atlantic salmon is not readily controllable by application of bacteriophage.     

Determination of mortality in exploited freshwater pearl mussel (Margaritifera margaritifera) populations

Estimates of mortality, based on relative numbers of live mussels and empty shells observed were obtained for a sample of seven exploited Scottish freshwater pearl mussel (Margaritifera margaritifera) populations. Total mortality (Z) estimates ranged from 0.058 to 0.189 year⁻¹ and fishing mortality (F) estimates ranged from 0.005 to 0.129 year⁻¹. General trends of increasing Z and F with age were apparent. Pearl fishers generally targeted larger, older mussels. In one heavily exploited population, the Z and F estimates converged, indicating that most of the mortality in older mussels (>50 years) was due to the effects of destructive pearl fishing. Since a complete ban on pearl fishing was introduced in 1998, illegal pearl fishing has continued albeit at a reduced level.     

Ammonia and pH effects on some metabolic parameters and gill histology of silver catfish, Rhamdia quelen (Heptapteridae)

The aim of the present study was to assess the effect of ammonia exposure at different pH on survivorship and metabolic parameters in the liver, muscle and gill histology of silver catfish (Rhamdia quelen). The 96 h-LC50 of un-ionized ammonia (mg L^− 1) at pH 6.0, 7.5 and 8.2 were: 0.44 (C.I. 0.38–0.49), 1.45 (C.I. 1.25–1.65) and 2.09 (C.I. 1.85–2.36), respectively. Survival of juveniles exposed to different ammonia levels was altered by pH, and fish exposed to all ammonia levels and different pH showed muscle glucose, muscle and liver glycogen reduction. Liver glucose and muscle and liver lactate levels increased in all fish exposed to ammonia as compared to the control. Exposure to waterborne ammonia increased total ammonia levels in both tissues and also induced gill epithelium damages such as lamellar fusion and edema as compared with controls at different pH. Silver catfish exposed to pH 6.0 and different NH₃ levels presented significantly higher hepatic glucose and protein levels when compared to those maintained at low NH₃ levels. Juveniles exposed to NH₃ levels at pH 7.5 and 8.2 showed lower hepatic protein levels compared to those maintained at low NH₃ levels. These parameters are indicative of pH dependence on ammonia toxicity in silver catfish. The metabolic parameters and gill histology may be used as early indicators of ammonia toxicity in silver catfish.     

Effect of ammonia on the growth rate and oxygen consumption of juvenile greenlip abalone, Haliotis laevigata Donovan

Juvenile greenlip abalone, Haliotis laevigata, (mean whole weight 4.48±1.9 g, mean±s.d., n=953) were highly sensitive to ammonia as indicated by depressed growth rate and food consumption measured over 2–3 months in bioassay tanks. For growth rate expressed on a whole weight basis, the EC₅ and EC₅₀ values (5 and 50% growth reductions) were 0.041 mg FAN l⁻¹ (Free Ammonia–Nitrogen) and 0.158 mg FAN l⁻¹, respectively. Shell growth rates declined over the entire experimental range (0.006–0.188 mg FAN l⁻¹). At the end of the bioassay, groups of abalone were transferred to respiratory chambers. Oxygen consumption rate increased to a maximum of 188% of control values at 0.235 mg FAN l⁻¹ and decreased slightly at the highest concentration of 0.418 mg FAN l⁻¹.     

Feeding has the largest effect on the ammonia excretion rate of the southern rock lobster, Jasus edwardsii, and the western rock lobster, Panulirus cygnus

The total ammonia nitrogen (TAN) excretion of spiny lobsters Jasus edwardsii and Panulirus cygnus, was determined in relation to temperature, body weight, emersion, daily rhythm and feeding. Temperature and body weight had large influences on the rate of TAN excretion. Exponential relationships were found between temperature (T) and TAN excretion of both species. These were described by the following equations: J. edwardsii Log₁₀ TAN=0.041T−3.57 (r²=0.979, F=143.2, P=0.001), P. cygnus Log₁₀ TAN=0.057T−3.90 (r²=0.987, F=302.2, P<0.001). TAN excretions of both species were positively correlated to body weight (W), and the relationships were described by the following equations: J. edwardsii Log₁₀ TAN=0.473 log₁₀ W−1.704 (r²=0.42, F=14.05, P=0.001), P. cygnus Log₁₀ TAN=0.499 log₁₀ W−1.346 (r²=0.69, F=44.18, P<0.001). TAN excretion increased significantly when lobsters were re-immersed after a 30 min period of emersion. However, it returned to pre-emersion levels by the second hour of re-immersion. Daily rhythm resulted in a significantly higher nocturnal TAN excretion rate for J. edwardsii; no daily rhythm was observed for P. cygnus. Feeding had the largest influence on TAN excretion, with maximum increases of 6.28 (J. edwardsii) and 5.60 (P. cygnus) times the pre-feeding level. TAN excretion rates remained significantly higher than the pre-feeding levels for an extended period (26 h, J. edwardsii; 30 h, P. cygnus). Implications for the use of purging tanks in lobster holding facilities and for the design of biofiltration systems are discussed.     

金沙江中下游细鳞裂腹鱼的年龄生长及种群动态

探究金沙江中下游细鳞裂腹鱼(Schizothorax chong)的年龄、生长及种群动态,可为其资源保护提供理论依据。2013-2017年在金沙江中下游干流攀枝花、巧家及其支流雅砻江、黑水河下游江段采集细鳞裂腹鱼170尾,逐尾测量全长、体长、体重,取臀鳞与微耳石为年龄鉴定材料,研究细鳞裂腹鱼的年龄结构、生长特征与种群动态。结果表明,金沙江中下游细鳞裂腹鱼以低龄个体(1~3龄)为主,臀鳞及耳石均能够作为其低龄个体的年龄鉴定材料;细鳞裂腹鱼体重(W)和体长(L)关系式为W=7.00×10^-6L^3.1885(R²=0.9867,n=170),雌雄个体间体长-体重关系无显著性差异(P>0.05);渐进体长(L_∞)为774.74 mm,生长系数(k)为0.13,理论生长起点年龄(t 0)为-0.13龄;渐进体重(W∞)为11407.01 g,体长生长方程为L_t=774.74[1-e^-0.13(t+0.13)],体重生长方程为W_t=11407.01[1-e^-0.13(t+0.13)^]3.1885,拐点年龄为8.79龄;种群总死亡系数(Z)为0.82,自然死亡系数(M)为0.26,当前开发率(E)为0.68,高于理论最大开发率(E_max)0.388;相对单位补充渔获量和生物量的结果也表现为过度捕捞特征,种群已处于过度利用状况。针对细鳞裂腹鱼的生态习性特征及其资源现状,建议采取生态调度、支流栖息地恢复及控制非法电捕等措施以保护其资源。     

Using a macroalgae Ulva pertusa biofilter in a recirculating system for production of juvenile sea cucumber Apostichopus japonicus

A simple indoor recirculating system for production of juvenile sea cucumber (Apostichopus japonicus) was operated on a commercial scale for 90 days during winter. The system consists of three 70 m³ sea cucumber rearing tanks and one biofilter tank where macroalgae (Ulva pertusa) was used as a biofilter in order to reduce water requirements. Effluent from the sea cucumber tanks drained into the macroalgae biofilter tank and were then returned to the sea cucumber tanks by a discontinuous-flow recirculation system. Survival and growth rates in the sea cucumber culture tanks were similar to those in the control tank (with one water exchange per day). The survival rate averaged about 87%. The average body weight increased from 3.5 ± 0.3 g to 8.1 ± 0.8 g and total sea cucumber biomass production over the experimental period was 745 g m⁻² after initial stocking densities of 375 g m⁻². The growth rate of U. pertusa was 3.3% day⁻¹. U. pertusa was efficient in removing toxic ammonia and in maintaining the water quality within acceptable levels for sea cucumber culture; there were only small daily variations of temperature, pH and DO. The U. pertusa tank removed 68% of the TAN (total ammonia-nitrogen) and 26% of the orthophosphate from the sea cucumber culture effluent; the macroalgae biofilter removed ammonia at an average rate of 0.459 g N m⁻² day⁻¹. It would be efficient to use the U. pertusa biofilter in a recirculating system for production of A. japonicus juveniles in winter.     

The effects of the decomposition of mangrove leaf litter on water quality, growth and survival of black tiger shrimp (Penaeus monodon Fabricius, 1798)

An experiment was conducted for 8 weeks at the Cantho University, Vietnam, to determine the acceptable level of mangrove leaf litter load and its effect on water quality, growth and survival rate of tiger shrimp (Penaeus monodon). Shrimps were cultured in plastic tanks containing 50 L of brackish water (salinity of 15‰). Leaf litter of Rhizophora apiculata, Avicennia officinalis, Excoecaria agallocha and Acacia auriculiformis were loaded to tanks at rates of 0.0 (control), 0.125, 0.25, 0.5, 1.0 and 2.0 g L^− 1 with and without aeration. Tiger shrimp post-larvae (PL; 0.05 ± 0.01 g) obtained from the shrimp hatchery of Cantho University were stocked at a density of 20 PL per tank and fed with pelleted feed containing 38% protein at a rate of 10% body weight (BW) day^− 1.

The high leaf-loading rates significantly reduced dissolved oxygen (DO) and survival rates of shrimp in the non-aerated treatments, and all shrimps died after 2 days in the treatments with loading rates above 0.5 g L^− 1. Leaf litter loads significantly increased tannin content, chemical oxygen demand (COD), H₂S and pH in the aerated treatments. Stepwise regression analysis showed COD, tannin and H₂S concentrations had negative effects on shrimp growth in the aerated treatments. Tannin concentration was found to be highest in the treatments with Excoecaria (32 mg L^− 1) and Avicennia (24 mg L^− 1) leaves. However, there were no significant differences in growth and survival rates of shrimp among the aerobic treatments loaded with different leaf types. The results of this study showed that moderate load of mangrove leaves could play an important role in promoting shrimp growth and survival in aerobic condition. Mangrove leaves at a loading rate of 1 g L^− 1 positively influenced both the survival and growth rate of shrimps.     

Estimate of reproductive value of the big eye Priacanthus macracanthus in the north-eastern waters off Taiwan

ABSTRACT: The reproductive value and population status of the big eye in the north-eastern Taiwan waters was estimated by demographic analysis using available life-history parameters. Life-history tables were constructed using estimates of natural mortality ( M ) of 10.4920/year for age 0 and 0.3256/year for ages 1–9, with a maximum age of 9. Age-specific batch fecundity ( F_e ) was from F_e  = 1391.34e^{0.1782 FL} . The age-specific proportion of maturity was estimated from the relationship between the proportion of female maturity ( Pr ) and fork length ( FL ): Pr  = 1/(1 + e^{15.081−0.796 FL} ). Females mature at age 3 and mature females reproduce every year. The population increase rate (λ) was estimated to be 20.5% per year and the generation time ( G ) was 6.25 years without exploitation. The net reproductive value ( R₀ ), generation time and intrinsic rate of natural increase ( r ) decreased with increased fishing mortality. For fixed fishing mortality, when F  = 1.2/year and fishing started at age 3, R₀ was estimated to be 1.0 and the population was considered to be in equilibrium. For age-specific fishing mortality, when fishing started at age 3, R₀ was estimated to be 0.96/year, G being 6.18 years, and the population decreased 0.7% per year. The big eye population had a strong resilience as long as F  < = 1.3/year started at an age that was older than the age at maturity (i.e. 3 years old) but would decline when intensive fishing ( F  > = 1.2/year) started at age 2 or younger. Sensitivity analysis indicated that the mortality of age 0 is the most sensitive parameter in demographic analysis.