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.     

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).     

Evidence for fine geographical scale heterogeneity in gene frequencies in yellowfin tuna (Thunnus albacares) from the north Indian Ocean around Sri Lanka

Yellowfin tuna are currently considered by the member nations of the Indian Ocean Tuna Commission to constitute a single stock in the Indian Ocean due to a lack of knowledge about yellowfin tuna population structure in this region. Previous studies of Indian Ocean yellowfin tuna based on morphology and fisheries data have hinted at the presence of multiple stocks in the region, and further, that stocks may mix in the north western Indian Ocean around Sri Lanka. To better understand the genetic stock structure of yellowfin tuna in the north western Indian Ocean, we examined genetic variation in 285 yellowfin individuals collected over a period of 4 years from six fishing grounds around Sri Lanka and a single fishing ground in the Maldive Islands. We screened variation in both the mitochondrial ATPase 6 and 8 region (498 bp) and three microsatellite loci. Significant genetic differentiation was detected among sites for mitochondrial DNA (Φ_ST = 0.1285, P < 0.001) and at two microsatellite loci (F_ST = 0.0164, P < 0.001 and F_ST = 0.0064, P < 0.001), while spatial analysis of molecular variance of mtDNA data identified three genetically heterogenous groups namely; western, south eastern and all remaining sites. These results suggest the possibility that genetically discrete yellowfin tuna populations may be present in the north western Indian Ocean.     

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.     

The dynamics of an exploited population of a siluroid catfish (Schilbe intermidius Reupell 1832) in the Cross River, Nigeria

We studied the breeding biology, growth, mortality, recruitment pattern and yield per recruit of a freshwater siluroid catfish (Schilbe intermedius) in the Cross River, Nigeria. Monthly variation in mean gonadosomatic and mean condition indices shows that the species breeds twice in a year (March and September). We used 12 consecutive months length–frequency data together with FiSAT software to study the population dynamics of this catfish which is exploited by artisanal fishermen. Fitting the seasonalized von Bertalanffy growth function to our length–frequency data gives the following growth parameters: L_∞=27.5 cm total length, K=0.29 yr⁻¹, C=0.5, WP=0.46. Using the seasonalized length converted catch curve, we estimated the instantaneous total mortality coefficient Z as 1.85 yr⁻¹. The instantaneous natural mortality coefficient M was 0.81 yr⁻¹ while the instantaneous fishing mortality coefficient F was 1.04 yr⁻¹, giving the current exploitation rate E=0.56. From the analysis of probability of capture of each length class we estimated the length at first capture L_c to be 10.9 cm. The relative yield per recruit analysis predicted the maximum exploitation rate E_max=0.54. The current exploitation rate E is more than this predicted maximum E_max. Thus, the species is on the verge of being overexploited.     

Evaluation of genetic diversity of eight grouper species <Emphasis Type="Italic">Epinephelus</Emphasis> spp. based on microsatellite variations

ABSTRACT:   Genetic diversity among eight species of grouper, Epinephelus bleekeri , E. coioides , E. malabaricus , E. ongus , E. akaara , E. maculatus , E. merra and E. fuscoguttatus , was studied using six microsatellite loci, Em-01 *, Em-03 *, Em-07 *, Em-08 *, Em-10 *, and CA-07 *, with the aim of exploring the feasibility of using microsatellite data for species identification. The results showed high levels of genetic differentiation among species ( F _ST  = 0.4403 and R _ST  = 0.4954). Species identification based on fixed allelic differences was possible between E. coioides , E. ongus , and E. fuscoguttatus at Em-01 * and between E. fuscoguttatus and E. ongus at Em-08 *. Private alleles were found in all species, except for E. ongus . Pairwise F _ST ranged 0.238–0.578 ( P  < 0.008 Bonferroni correction), and Nei's genetic distance ranged 0.433–2.710. Size homoplasy was observed at Em-03 * 157 allele, which was characterized by a T–C transition at the 119th nucleotide site of PCR products. The genetic assignment test unambiguously assigned each individual to the correct species. Thus, this test can be used for species identification of unknown individuals when the multilocus genotypes of the six microsatellite loci are available. The phylogenetic (neighbor-joining) tree, which was constructed based on the genetic distance matrix, separated the eight grouper species into two main groups.     

Proximate composition of some north-eastern Pacific forage fish species

To understand the relative dietary value of forage fish as prey in the Bering Sea and Gulf of Alaska, whole organisms of 13 species were analysed for proximate composition (protein, oil, ash and moisture content). Eulachon ( Thaleichthys pacificus ) were high in oil (total lipid) (16.8% to 21.4%) and low in moisture (64.6% to 70.8%). Oil in capelin ( Mallotus villosus ) ranged from 2.1% to 14.0%. Juveniles of walleye pollock ( Theragra chalcogramma ), Atka mackerel ( Pleurogrammus monopterygius ), Pacific herring ( Clupea pallasii ), and prowfish ( Zaprora silenus ) had low oil contents (< 1.8%) and high moisture contents (> 80.3%). Rankings of median proximate values illustrate the similarities. Surf smelt ( Hypomesus pretiosus ), rainbow smelt ( Osmerus mordax ), pricklebacks ( Lumpenus spp.), Atka mackerel, Pacific sand lance ( Ammodytes hexapterus ) and Pacific sandfish ( Trichodon trichodon ) ranked high in median protein content (> 15.4%). Median ash content for all species ranged from 0.6% to 3.3%. Total wet mass caloric content (kcal g^–1) was calculated for the four main species and a linear model was developed for caloric content as a function of moisture. The linear models (caloric content = b₀ + b₁ × moisture) were Pacific sand lance and Pacific sandfish (b₀ = 7.82, b₁ = – 0.09); eulachon (b₀ = 7.97, b₁ = – 0.08); and capelin (b₀ = 9.70, b₁ = – 0.11).     

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.     

Effect of hyperoxygenation and low water flow on the primary stress response and susceptibility of Atlantic salmon Salmo salar L. to experimental challenge with IPN virus

Intensive salmon smolt production normally includes reduced water flow and hyperoxygenation (added oxygen) of remaining water. There is little information on how different water quality parameters influence the fish health and the susceptibility to infectious diseases. The current experiment was carried out to evaluate if the combination of hyperoxygenation and reduced water flow (hyperoxic) can act as a chronic stressor to salmon in freshwater (FW) in such a way that it increases the susceptibility to IPN virus (IPNV) following seawater transfer. In FW, after 22 days of hyperoxic exposure plasma ion, TBARS and cortisol were measured. The cortisol levels were significantly (p = 0.011) higher in the hyperoxic group compared to controls maintained under normal oxygen saturation and water flow (normoxic), indicating chronic stress. Hyperoxygenation in FW caused decreased plasma [Cl⁻] compared to the normoxic group (p = 0.037), while [K⁺] tended to be higher in the hyperoxic group (p = 0.088). No significant differences were observed in plasma [Na⁺], total osmolality, TBARS or hematocrit, but there was a tendency towards a lower hct in the hyperoxic compared to the normoxic group. In SW the mortality was higher in the hyperoxic group challenged with IPNV (34%) compared to the normoxic group challenged with IPNV (20%) (p = 0.02), and no mortality was observed in the PBS injected fish. The challenged fish showed an overall increase in plasma cortisol day 8, 10, 12 and 14 post-challenge (p = 0.015, p = 0.000, p = 0.046 and p = 0.022 respectively). After SW transfer and challenge, plasma [K⁺] was elevated in both challenged groups, but no consistent trends were found for plasma [Cl⁻], [Na⁺] or total osmolality during the SW phase. There were no significant differences in the gene expression level of IFN 1, Mx and IL 1β prior to challenge, suggesting that the basic expression level of these genes were not affected by hyperoxygenation. IPNV was detected in kidney and pylorus, by immunohistochemistry, cell culture, and RT-PCR in head kidney. This experiment indicates that chronic stress induced by a combination of low water flow and hyperoxygenation increases the susceptibility to IPNV challenge.     

Breeding and juvenile culture of the lined seahorse, Hippocampus erectus Perry, 1810

All seahorse species worldwide have been placed under CITES Appendix II since 2004, because they have been over-exploited for traditional Chinese medicine and aquarium trades. Aquaculture has been recognized as a long-term solution for sustaining the seahorse trade while minimizing wild collection. In this study, we evaluated the breeding and juvenile culture of an important aquarium seahorse species, the lined seahorse Hippocampus erectus, Perry 1810. Pairing, mating and copulation behavior were observed. Gestation time and brood size were 17.33 ± 2.94 days and 272.33 ± 66.45 individuals/brood, respectively. Growth rates differed among juveniles from different broods. Effects of temperature on the growth rates and survivorship of the juveniles during the first two weeks were compared. The highest growth rate and survivorship of the juveniles occurred at 28–29 °C among the temperatures tested (24–33 °C). Growth rate and survivorship of the juveniles during the first 9 weeks at 28 °C were investigated. The final standard length and survivorship of the juveniles were 6.32 ± 0.52 cm and 71.11 ± 10.18%, respectively, and the relationship between the wet weight and the standard length of the juvenile seahorses can be expressed as: W = 0.0034 L^2.5535 (r² = 0.9903, n = 12, P < 0.01). These findings suggest that H. erectus is a good candidate for commercial aquaculture.     

Survival of Clarias gariepinus fry in earthen ponds: Effects of composts and leaks

To inform decisions on improving the yields of African catfish Clarias gariepinus fingerlings in earthen ponds, the hypothesis that composts and leaks were partly responsible for usually low and variable fry survivals was tested, through comparison of treatments and simple regression. The occurrence of amphibians was significantly higher (P < 0.05) and survival of fry was significantly lower (P < 0.02) in ponds with composts than in those without. The survival of fry and fingerlings in earthen ponds was negatively correlated with their night leaking rates and regression analysis yielded the equations y = − 13.31x + 82.56 for fry and y = − 6.97x + 95.29 for fingerlings, where y is the survival of fry or fingerlings in a holding pond and x is the leaking rate of the pond. Realizing how negatively the existence of composts and leaks could affect the survival of fry and fingerlings, fertilizing unfenced ponds with composts and sterilizing nursery ponds by drying were proscribed.     

Selectivity in a trawl codend during haul-back operation—An overlooked phenomenon

The selectivity of a 99 mm trawl codend was assessed using a codend cover fitted with a MultiSampler, which was acoustically triggered to take separate samples at three different phases of the haul. The first sample was collected during towing, the second during haul-up and the third at the surface. A total of 18 hauls were conducted with a commercial fishing vessel west of Scotland. It was demonstrated that escapes take place not only during the tow but also in the short period when the trawl is hauled back from the seabed and when the codend is at the surface. For haddock (Melanogrammus aeglefinus), whiting (Merlangius merlangus) and Norway lobster (Nephrops norvegicus), respectively, the mean percentages escaping at the surface were 16, 12 and 38% of the total escape while 17, 8 and 28% escaped during the haul-up phase. Compared to towing, the escape rate (no./min) increased for haddock by a factor 2.7 during haul-up and by a factor 1.7 at the surface, whereas the escape rates of whiting were similar for the three phases. The escape rate of Norway lobster increased by a factor of approximately 7 for both the haul-up and surface phases, compared to the towing phase. The selectivity parameters L50 (50% retention length) and SR (selection range = L75–L25) were estimated and compared for the three different phases and for the whole haul for haddock, whiting and Norway lobster. For all three species there was no significant (P > 0.05) difference in L50 between the three phases of the haul. There was also no significant difference for whiting and Norway lobster when comparing the SR of the three phases, whereas the SR was significantly lower for haddock when comparing the surface phase with towing and haul-up. The estimate of L50 when towing was about 6 cm lower for haddock and whiting and 9 mm for Norway lobster compared to the selection curve estimated conventionally for the whole haul. Finally, the effect of sea state, duration and codend catch on the selectivity parameters were estimated for the individual phases and for the whole haul. A significant effect of at least one variable was found in all phases.     

Target strength estimation of black porgy Acanthopagrus schlegeli using acoustic measurements and a scattering model

ABSTRACT:   Black porgy are hatched and released in marine ranching areas in Japan, Korea and Taiwan to maintain fisheries resources in coastal areas. If acoustic methods are used for field surveys, target strength ( TS ) information on the species is needed to convert acoustic data to biomass density. Target strength of black porgy ( Acanthopagrus schlegeli ) 15.5–32.9 cm fork length (nine individuals) was measured at 38 and 120 kHz (split beam) by ex situ measurements (cage and fishhook methods) of living fish, a tethered method with shock-frozen fish, and an acoustic scattering model, the Kirchhoff ray mode (KRM) model based on fish morphology. The ex situ TS -to-fork length ( FL , cm) relationships were TS _38kHz = 20log₁₀ FL  − 64.6 ( r  = 0.77) and TS _120kHz = 20log₁₀ FL  − 65.2 ( r  = 0.70). The values for the KRM model were TS _38kHz = 20log₁₀ FL  − 64.8 ( r  = 0.88) and TS _120kHz = 20log₁₀ FL  − 65.4 ( r  = 0.80). The agreement between the ex situ measurements and the KRM model for the mean TS was very good. In contrast, the results for the tethered method ( TS _38kHz = 20log₁₀ FL  − 69.3 [ r  = 0.42]) differed markedly from the other two methods, perhaps because of the effects of the shock-freezing procedure in air. The results of the ex situ measurements and scattering model provide basic information for studying TS and conducting acoustic surveys of black porgy, even though the tethered method must be modified.     

Age,growth and age at sexual maturity of fan ray <Emphasis Type="Italic">Platyrhina sinensis</Emphasis> (Batoidea: Platyrhinidae) in Ariake Bay,Japan

Abstract:   Age, growth and sexual maturity of the fan ray Platyrhina sinensis in Ariake Bay, Japan were determined from specimens collected from May 2002 to September 2006. Age determination was conducted by vertebral centrum analysis using soft X-radiography. Annual band pair deposition was determined by marginal increment and edge analyses. The von Bertalanffy growth model best described the overall pattern of growth for both males and females (males L _∝  = 455.2, k  = 0.56, t ₀ = −1.09; females L _∝  = 555.8, k  = 0.28, t ₀ = −1.77; L _∝ is the theoretical asymptotic total length in mm, k is the growth rate coefficient and t ₀ is the theoretical time at zero length). Parameter estimates suggest that females attain a larger asymptotic total length and grow more slowly than males. The observed maximum ages were 5 years for males and 12 years for females. Age at 50% sexual maturity was 2.1 years for males and 2.9 years for females. The results indicate that this species is relatively fast-growing, short-lived and early maturing compared with many batoid species.     

Growth performance of weaning red abalone (Haliotis rufescens) fed with Macrocystis pyrifera plantlets and Porphyra columbina compared with a formulated diet

A feeding experiment was carried out to evaluate two natural diets versus a formulated feed on the performance of weaning red abalone Haliotis rufescens . Four treatment diets were then investigated: a formulated diet; plantlets from culture Macrocystis pyrifera, Porphyra columbina from natural beds; and a mixed diet consisting of a blend of fresh P. columbina together with the formulated diet. This study was performed in a shallow aquaculture system with a horizontal water flow. After 90 days, significant differences were observed between treatments. The highest growth was obtained with Porphyra (3.3 mm month⁻¹), followed by the mixed diet (2.6 mm month⁻¹), then Macrocystis (2.1 mm month⁻¹) and lastly the formulated diet (1.4 mm month⁻¹). Moreover, after the diets were tested for stability and remnant nutrients after a 12-h water immersion, a positive trend appeared to be related to the protein/energy (P:E). It is concluded that fronds of P. columbina resulted in the best diet for weaning H. rufescens under horizontal water flow systems, even if apparently the water stability of the formulated diet had a negative impact on abalone performance, particularly due to a poor nutrient retention capacity. Therefore, formulated diets should be improved before being recommended for weaning red abalone.     

Characterization of 38 kDa and 42 kDa chitinase isozymes from the liver of Japanese common squid Todarodes pacificus

ABSTRACT: Characterization was investigated on the 38 kDa and 42 kDa chitinase (EC3.2.1.14) isozymes from the liver of Japanese common squid Todarodes pacificus . Optimum pH toward colloidal chitin was observed at pH 3.0 for the 38 kDa chitinase, and pH 3.0 and 9.0 for the 42 kDa chitinase. K _m and k _cat of the 38 kDa and 42 kDa chitinases toward a longer substrate, glycol chitin, were 0.071 mg/mL and 1.22/s, and 0.074 mg/mL and 0.196/s, respectively. Alternatively, strong substrate inhibition of both chitinases were observed toward a short substrate, N -acetylchitopentaose (GlcNAc₅). Both chitinases decomposed not only chitin but also chitosan (D. A. 95%). The cleavage pattern and reaction rate were investigated using N -acetylchitooligosaccharides (GlcNAc_n, n  = 2–6). Both chitinases hydrolyzed GlcNAc_n ( n  = 4,5, and 6). The release of GlcNAc was not observed. The speed of the reaction was observed to be in the following order: GlcNAc₄ > GlcNAc₅ > GlcNAc₆ for the 38 kDa chitinase, and GlcNAc₆ > GlcNAc₅ > GlcNAc₄ for the 42 kDa chitinase. Both the chitinases released p -nitrophenol from p -nitrophenyl GlcNAc_n ( n  = 2, 3, and 4). N-terminal amino acid sequences of the 38 kDa and 42 kDa chitinases were YLLSXYFTNWSQYRPGAGKYFPQNI and EYRKVXYYTNWSQYREVPAKFFPEN, respectively.     

Growth of juvenile tilapia, Oreochromis niloticus L. from Lakes Zwai, Langeno and Chamo (Ethiopian rift valley) based on otolith microincrement analysis

Abstract – Age and growth of juvenile tilapia, Oreochromis niloticus , from Lakes Zwai, Langeno and Chamo (Ethiopia) were studied from microincrements in otoliths. Growth in length was best described by the Gompertz model. Average growth rate of the fish was most rapid in Lake Chamo (0.39 mm  ·  day⁻¹, 1.14%  ·  day⁻¹), intermediate in Lake Zwai (0.20 mm  ·  day⁻¹, 0.72%  ·  day⁻¹) and slowest in Lake Langeno (0.16 mm  ·  day⁻¹, 0.62%  ·  day⁻¹). Similarly, back-calculation from otolith increment widths gave growth rates of 0.28 to 0.43 mm  ·  day⁻¹, 0.15 to 0.32 mm  ·  day⁻¹ and 0.11 to 0.28 mm  ·  day⁻¹ for Chamo, Zwai and Langeno fish, respectively. In addition, Fulton's condition factor was largest for Chamo tilapia and smallest for Langeno tilapia; the difference between fish from Langeno and Zwai was small. Rapid growth of juvenile O. niloticus in Lake Chamo was attributed to warm temperature and better food quality. ^Note     

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.     

Pharmacokinetics and the active metabolite of enrofloxacin in Chinese mitten-handed crab (Eriocheir sinensis)

The pharmacokinetics and active metabolite of enrofloxacin were estimated after single intramuscular administration (10.0 or 20.0 mg/kg body weight) to the Chinese mitten-handed crab (Eriocheir sinensis) in fresh water at 25.0 ± 1.0 °C. Levels of enrofloxacin and its metabolite ciprofloxacin in the main tissues (hemolymph, hepatopancreas, muscle, ovary and spermary) were simultaneously detected by HPLC. Enrofloxacin concentration–time profiles for the hemolymph in both tests were described by a two-compartment open model with first-order absorption. Distribution half-time (T_1/2), elimination half-time (T_1/2β), body clearance (CL/F), mean residence time (MRT_0–∞), area under the concentration–time curve from 0 to ∞ h (AUC_0–∞) and apparent volume of distribution (Vd/F), which derived from the pharmacokinetic model, were 0.427 h, 21.3 h, 0.133 l/h/kg, 60.0 h, 96.9 μg/ml/h and 4.08 l/kg, respectively, at a dose of 10.0 mg/kg body weight, and 0.216 h, 12.3 h, 0.189 l/h/kg, 85.8 h, 187 μg/ml/h and 3.35 l/kg, respectively, at a dose of 20.0 mg/kg body weight. Similarities were found between the hemolymph concentration–time curves of the two tests; for example, instant absorption process followed by the distribution phrase, and a second absorption peak at 6 h post-treatment. After intramuscular administration of 10.0 mg/kg body weight, absorption of enrofloxacin was observed in the main edible tissues (hepatopancreas, muscle, ovary and spermary), and the drug residue was the highest in the hepatopancreas, where the ‘drug sink’ phenomenon occurred. Comparative pharmacokinetics showed fast absorption, broad distribution and fast elimination of enrofloxacin in E. sinensis after intramuscular dosing. Regarding ciprofloxacin, the main active metabolite of enrofloxacin, though relatively low levels were detected in all the main tissues of the crab, its kinetics in the hemolymph in the two tests were not described by a one- or two-compartment open model.     

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.