Improving sustainable yield estimates for tropical reef fisheries

Fishing sustainably is a fundamental problem in tropical regions where diverse fisheries and scarce fisheries information challenges efforts to make reliable estimates and associated policies. To improve evaluations and decisions, we compared the predictions of six surplus production models calibrated using various permutations of fisheries‐dependent data with a benchmark model. The benchmark model was built from fisheries‐independent estimates of r and K, tested against rates of change in Kenyan reef fisheries and found to be accurate. Comparisons with the benchmark model were made with fisheries‐dependent equilibrium and non‐equilibrium models, fixing or not fixing r and K, pooled versus site averaged solutions, and rising, falling, and pooled fishing effort over time. Evaluations indicate high variability in MMSY predictions and notable overestimates of MMSY (~75%) and effort (~210%) for Fox and Schaefer equilibrium models. Non‐equilibrium models had high failure rates (~25%) but successful fits performed better and indicated smaller overestimates (16%) for site‐level evaluations. The Pella–Tomlinson model was most accurate (MMSY = 5.6 ± 0.60 (SD) tonnes/km²/year) and best‐fit r‐K relationships also aligned well with ecoregional data on K and short‐term yields. Future efforts are advised to pool site data, use conservative recruitment values (z = 0.8), and collect data across times of both rising and falling effort. Recommended methods and subsequent adjustments of the benchmark model should improve local and ecoregional scale MMSYs. The benchmark model was calibrated to estimate MMSY in fished seascapes, but to conserve species with slower life histories, we suggest modifications to limit MMSYs to between 1.8 and 3.2 tonnes/km²/year.     

Effects of replacing fish meal with mussel (Cristaria plicata) meat on growth,digestive ability,antioxidant capacity and hepatic IGF‐I gene expression in juvenile Ussuri catfish (Pseudobagrus ussuriensis)

An 8‐week feeding trial was implemented to evaluate the effects of replacing fish meal (FM) with mussel (Cristaria plicata) meat (MM) on growth, digestive ability, antioxidant capacity and hepatic insulin‐like growth factor I (IGF‐I) gene expression of juvenile Ussuri catfish (Pseudobagrus ussuriensis). Three isonitrogenous and isolipidic diets were formulated to include 0, 177.5 and 355.1 g/kg of MM, accordingly, replacing 0% (M₀, control), 50% (M₁) and 100% (M₂) of FM protein, respectively. The results showed that the final body weight, weight gain, specific growth rate and feed intake were gradually decreased with dietary MM protein levels increased, but there were no significant difference between M₀ and M₁ groups (p > 0.05). The protein efficiency ratio was increased significantly with dietary MM inclusion (p < 0.05). The apparent digestibility coefficient of dry matter, crude lipid and gross energy gradually increased with increasing dietary MM protein levels, but the apparent digestibility coefficient of crude protein was not significantly affected by MM protein supplementation (p > 0.05). Fish fed diet, M₀ and M₁ remained unaffected significantly on activities of alpha‐amylase and pepsin (p > 0.05), but fish fed diet M₂ had the highest activities of alpha‐amylase and pepsin. Fish fed diet M₁ or M₂ had significantly lower hepatic total antioxidant capacity, superoxide dismutase and the higher malondialdehyde level compared to fish fed diet M_0. In addition, no significant difference was observed in hepatic IGF‐I gene expression level for fish fed diet M₀ and diet M₁, and fish fed diet M₂ showed significantly lower hepatic IGF‐I gene expression level. Therefore, we can conclude that MM protein can successfully substitute 50% of FM protein without significantly negative effect on growth, nutrient utilization, and hepatic IGF‐I gene expression for juvenile Ussuri catfish, but the antioxidant capacity was negatively affected in the present study, what is more, the total replacement of FM by MM in diet may result in the inhibition of the growth and antioxidant capacity of fish.     

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.     

Extensive dispersal of Roanoke logperch (Percina rex) inferred from genetic marker data

The dispersal ecology of most stream fishes is poorly characterised, complicating conservation efforts for these species. We used microsatellite DNA marker data to characterise dispersal patterns and effective population size (N_e) for a population of Roanoke logperch Percina rex, an endangered darter (Percidae). Juveniles and candidate parents were sampled for 2 years at sites throughout the Roanoke River watershed. Dispersal was inferred via genetic assignment tests (ATs), pedigree reconstruction (PR) and estimation of lifetime dispersal distance under a genetic isolation‐by‐distance model. Estimates of N_e varied from 105 to 1218 individuals, depending on the estimation method. Based on PR, polygamy was frequent in parents of both sexes, with individuals spawning with an average of 2.4 mates. The sample contained 61 half‐sibling pairs, but only one parent–offspring pair and no full‐sib pairs, which limited our ability to discriminate natal dispersal of juveniles from breeding dispersal of their parents between spawning events. Nonetheless, all methods indicated extensive dispersal. The AT indicated unrestricted dispersal among sites ≤15 km apart, while siblings inferred by the PR were captured an average of 14 km and up to 55 km apart. Model‐based estimates of median lifetime dispersal distance (6–24 km, depending on assumptions) bracketed AT and PR estimates, indicating that widely dispersed individuals do, on average, contribute to gene flow. Extensive dispersal of P. rex suggests that darters and other small benthic stream fishes may be unexpectedly mobile. Monitoring and management activities for such populations should encompass entire watersheds to fully capture population dynamics.     

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.     

Estimating effective population size of large marine populations,is it feasible?

Sustainable exploitation of marine populations is a challenging task relying on information about their current and past abundance. Fisheries‐related data can be scarce and unreliable making them unsuitable for quantitative modelling. One fishery independent method that has attracted attention in this context consists in estimating the effective population size (N_e), a concept founded in population genetics. We reviewed recent empirical studies on N_e and carried out a simulation study to evaluate the feasibility of estimating N_e in large fish populations with the currently available methods. The detailed review of 26 studies found that published empirical N_e values were very similar despite differences in species and total population sizes (N). Genetic simulations for an age‐structured fish population were carried out for a range of population and samples sizes, and N_e was estimated using the Linkage Disequilibrium method. The results showed that already for medium‐sized populations (1 million individuals) and common sample sizes (50 individuals), negative estimates were likely to occur which for real applications is commonly interpreted as indicating very large (infinite) N_e. Moreover, on average, N_e estimates were negatively biased. The simulations further indicated that around 1% of the total number of individuals might have to be sampled to ensure sufficiently precise estimates of N_e. For large marine populations, this implies rather large samples (several thousands to millions of individuals). If however such large samples were to be collected, many more population parameters than only N_e could be estimated.     

Algal density alleviates the elevated CO2‐caused reduction on growth of Porphyra haitanensis (Bangiales,Rhodophyta), a species farmed in China

Growing of Pyropia haitanensis, a commercially farmed macroalga, usually increases their densities greatly during cultivation in natural habitats. To explore how the increased algal densities affect their photosynthetic responses to rising CO₂, we compared the growth, cell components and photosynthesis of the thalli of P. haitanensis under a matrix of pCO₂ levels (ambient CO₂, 400 ppm; elevated CO₂, 1,000 ppm) and biomass densities [low, 1.0 g fresh weight (FW) L^?1; medium, 2.0 g FW L^?1; high, 4.0 g FW L^?1]. Under ambient CO₂, the relative growth rate (RGR) was 5.87% d^?1, 2.32% d^?1 and 1.51% d^?1 in low, medium and high densities, and elevated CO₂ reduced the RGR by 27%, 25% and 12% respectively. Maximal photochemical quantum yield of photosystem II (F_V/F_M) was higher in low than in high densities, so were the light‐utilized efficiency (α), saturation irradiance (E_K) and maximum relative electron transfer rate (rETR_max). Elevated CO₂ enhanced the F_V/F_M in low density but not in higher densities, as well as the α, E_K and rETR_max. In addition, elevated CO₂ reduced the content of chlorophyll a and enhanced that of carotenoids, but unaffected phycoerythrin, phycocyanin and soluble proteins. Our results indicate that the increased algal densities reduced both the growth and the photosynthesis of P. haitanensis and alleviated the elevated CO₂‐induced negative impact on growth and positive impact on photosynthesis. Moreover, the elevated CO₂‐induced reduction on growth and promotion on photosynthesis indicates that rising CO₂ may enhance the loss of photosynthetic products of P. haitanensis through releasing organic matters.     

Effects of artificial selection practices on loss of genetic diversity in the Pacific abalone,Haliotis discus hannai

The Pacific abalone, Haliotis discus hannai Ino, is one of most important aquaculture species in China. Artificial selection has been the common and inevitable approach in breeding. In present study, the effect of artificial selection on the genetic structure of two abalone lines (JJ selection strain, three successive selection lines based on the fast‐growing trait, which was named JJF0, JJF1, JJF2, and JJF3; and R selection strain, the offspring of the red shell colored variants) were evaluated using 10 microsatellites. Loci showed from low to high polymorphism, with the number of alleles (A) ranging from 2 to 18 in each population. The mean observed (H_o) and expected heterozygosities (H_e) were 0.650 ± 0.022 and 0.711 ± 0.018, respectively. In selection strain JJ, the values for most diversity genetic indexes (A_e, the number of effective alleles, H_o and H_e) decreased from JJF0 to JJF3. Meanwhile, compared to JJ line, the genetic diversity estimates of R were close to those of JJF3. Nei's genetic distance ranged from 0.20357 to 0.51346. The unweighted pair group method with arithmetic mean tree based on Nei's genetic distance also showed that the control Japan population and JJF0 formed to a cluster firstly, which were subsequently grouped together with JJF1, JJF2, JJF3, whereas the R was isolated from the rest of the populations. Analysis of genetic information indicated that genetic diversity was lost with artificial selection practices. Mechanisms underlying the maintenance of an acceptable level of genetic diversity while pursuing economic interests should be conducted in future research studies.     

Setting the record straight on drivers of changing ecosystem states

This short communication is a response to the critique by Greene (2012), who puts forward the argument that the dynamics of northwest Atlantic continental shelf ecosystems are strongly influenced by changes in Arctic climate, as indexed by surface salinity. The argument, in its essence, discounts any indirect effects from over‐exploitation of top predators on lower trophic levels in northwest Atlantic ecosystems. Frank et al. (Science 308 , 2005, 1621; Nature 477 , 2011, 86) reported the existence of cascading trophic interactions with particular emphasis on the eastern Scotian Shelf. Greene argues that the events occurring in the Gulf of Maine/Georges Bank region are representative of all Northwest Atlantic shelf systems, despite previous research (Frank et al. Trends Ecol. Evol. 22 , 2007, 236; Petrie et al. Fish. Oceanogr. 18 , 2009, 83) that has shown a differential pattern of forcing ranging from top‐down in species‐poor, cold water systems to bottom‐up in warmer, more species‐rich systems, including Georges Bank.     

Tailoring codend mesh size to improve the size selectivity of undifferentiated trawl species

Tiger flathead, Neoplatycephalus richardsoni (Castelnau), and sand flathead, Platycephalus bassensis Cuvier, are undifferentiated and managed with a common legal minimum length (LML). The Commonwealth Trawl Sector (CTS) and the Tasmanian Danish‐seine fishery (TDSF) use a minimum codend mesh sizes of 90 and 70 mm, respectively. The codend mesh size should be tailored to the LML, which is based on the length of first maturity of females (M₅₀). This study found the length–girth relationship of N. richardsoni and P. bassensis was not significantly different. Using the covered codend method, these two species had 50% retention lengths (L₅₀) of 294 ± 2 and 307 ± 3 mm, in 70‐mm and 90‐mm codends, respectively. L₅₀ estimates for mesh sizes from this study and others produced a curvilinear relationship: y = 120 ln(x) ? 214, with an r² of 0.8504. The size at maturity (M₅₀) for female N. richardsoni was 337 mm, which is larger than the estimate for female P. bassensis (247 mm). There is a mismatch between the estimates of L_50, the estimates of M₅₀ and the LMLs in each fishery, leading to suboptimal exploitation of female Platycephalus. The model produced in this paper recommends a codend mesh size of 98 mm for both fisheries to exploit Platycephalus species sustainably.     

Revisiting safe biological limits in fisheries

The appropriateness of three official fisheries management reference points used in the north‐east Atlantic was investigated: (i) the smallest stock size that is still within safe biological limits (SSB_pa), (ii) the maximum sustainable rate of exploitation (F_msy) and (iii) the age at first capture. As for (i), in 45% of the examined stocks, the official value for SSB_pa was below the consensus estimates determined from three different methods. With respect to (ii), the official estimates of F_msy exceeded natural mortality M in 76% of the stocks, although M is widely regarded as natural upper limit for F_msy. And regarding (iii), the age at first capture was below the age at maturity in 74% of the stocks. No official estimates of the stock size (SSB_msy) that can produce the maximum sustainable yield (MSY) are available for the north‐east Atlantic. An analysis of stocks from other areas confirmed that twice SSB_pa provides a reasonable preliminary estimate. Comparing stock sizes in 2013 against this proxy showed that 88% were below the level that can produce MSY. Also, 52% of the stocks were outside of safe biological limits, and 12% were severely depleted. Fishing mortality in 2013 exceeded natural mortality in 73% of the stocks, including those that were severely depleted. These results point to the urgent need to re‐assess fisheries reference points in the north‐east Atlantic and to implement the regulations of the new European Common Fisheries Policy regarding sustainable fishing pressure, healthy stock sizes and adult age/size at first capture.     

Metabolic measurements and parameter estimations for bioenergetics modelling of Pacific Chub Mackerel Scomber japonicus

As a crucial step in developing a bioenergetics model for Pacific Chub Mackerel Scomber japonicus (hereafter chub mackerel), parameters related to metabolism, the largest dissipation term in bioenergetics modelling, were estimated. Swimming energetics and metabolic data for nine chub mackerel were collected at 14°C, a low temperature within the typical thermal range of this species, using variable‐speed swim‐tunnel respirometry. These new data were combined with previous speed‐dependent metabolic data at 18 and 24°C and single‐speed (1 fork length per second: FL/s) metabolic data at 15 and 20°C to estimate respiration parameters for model development. Based on the combined data, the optimal swimming speed (the swimming speed with the minimum cost of transport, U_opt) was 42.5 cm/s (1.5–3.0 FL/s or 2.1 ± 0.4 FL/s) and showed no significant dependence on temperature or fish size. The daily mass‐specific oxygen consumption rate (R, g O₂ g fish^?1 day^?1) was expressed as a function of fish mass (W), temperature (T) and swimming speed (U): R = 0.0103W^?0.490 e^(0.0457T) e^(0.0235U). Compared to other small pelagic fishes such as Pacific Herring Clupea harengus pallasii, Pacific Sardine Sardinops sagax and various anchovy species, chub mackerel respiration showed a lower dependence on fish mass, temperature and swimming speed, suggesting a greater swimming ability and lower sensitivity to environmental temperature variation.     

Bait worms: a valuable and important fishery with implications for fisheries and conservation management

Bait is an integral part of coastal life, but is perceived as a low‐value resource as fisheries are data‐limited, locally focussed and largely unregulated even though the ecological impacts of collection are considerable. An empirical assessment of three UK‐based ragworm fisheries combined with an analysis of published literature has produced the first global assessment of polychaete bait fisheries. The five most expensive (retail price per kg) marine species sold on the global fisheries market are polychaetes (Glycera dibranchiata, Diopatra aciculata, Nereis (Alitta) virens, Arenicola defodiens and Marphysa sanguinea). We estimate that 1600 t of N. virens per annum (worth £52 million) are landed in the UK with approximately 121 000 tonnes of polychaetes collected globally valued at £5.9 billion. Using remote closed circuit television (CCTV) cameras to monitor collectors, activity at local sites is considerable with a mean of 3.14 collectors per tide (day and night) at one site and individuals digging for up to 3 h per tide, although intensity differed seasonally and between sites. Collectors removed on average 1.4 kg of N. virens per person per hour, walking a considerable distance across the intertidal sediment to reach areas that were usually already dug. The implications of these human activity and biomass removal levels are explored in the context of fisheries and conservation management. At local, regional and national scales, polychaete bait fisheries are highly valuable, extract significant biomass and have considerable impacts; therefore, they urgently require governance equivalent to other fisheries.     

Can genetic diversity be maintained during mass selection of the Chinese mitten crab,Eriocheir sinensis?

The Chinese mitten crab (Eriocheir sinensis) is an important aquaculture species and food source in Eastern Asia. This study assesses the changes in genetic diversity in successive generations of early‐ and late‐maturing strains of E. sinensis using 30 microsatellite markers with high polymorphism. The mean average number of alleles (N) in the founder population (G0), first generation (G1), second generation (G2) and third generation (G3) of the early‐maturing strain were 18.367, 14.800, 16.400 and 16.533, respectively; while in late‐maturing strain the values were 18.500, 16.267, 14.367 and 16.533 respectively. Likewise, there was a slight decline in average allelic richness (R_s) in the three successive generations. In both strains, the mean observed heterozygosity (H_o) remained relatively constant for the early‐maturing strain and the values were 0.655, 0.667, 0.685 and 0.705, respectively; and for the late‐maturing strain these were 0.665, 0.672, 0.688 and 0.702 respectively. Similarly, the expected heterozygosity (H_e) remained constant, ranging from 0.823 to 0.854. There was a decrease in effective population sizes (N_e) of the early‐maturing strain with successive generations: values were 492.2, 35.0, 134.7 and 193.2, respectively; while the values in the late‐maturing strain were 1268.5, 75.6, 111.5 and 97.2 respectively. All pairwise population distances were very close in both strains. In conclusion, these results suggest that mass selection of E. sinensis did not significantly diminish genetic diversity although there was a decline for the N_e. Therefore, it is important to maintain sufficient broodstock numbers and a large effective population when following a selective breeding programme.     

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.     

Effects of a hook ring on catch and bycatch in a Mediterranean swordfish longline fishery: small addition with potentially large consequences

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Estimation of natural mortality using statistical analysis of fisheries catch-at-age data

This study utilized the fisheries catch-at-age data combined with the auxiliary information of effort data to calculate natural mortality rate (M), and the other population parameters such as catchability and recruitment. The method used in the paper was the standard statistical catch-at-age (SCA) model. Monte Carlo simulation data were used to test this method under four fishery scenarios (good contrast, one-way trip, recovery and status quo). This study showed that the quality of the annual recruitment greatly affected the estimated Ms. When the white noises (CVs) of recruitments reached 10% the estimated Ms were biased, even when the CVs of catch-at-age and effort data were low. CVs in catch-at-age and effort data were also important factors to affect the estimated M, and the results of the simulation analysis of three CV scenarios (CV in both of the catch-at-age and effort with the same level, CV in the catch-at-age (CV_C) was half of CV in the effort (CV_E) and CV_E was half of CV_C) indicated that CV_C made more effects than CV_E on the quality of the estimated M. Among the four fisheries, the one-way trip fishery outperformed the other three, since it obtained the lowest relative estimate error (REE) values of the estimated M for all the scenarios, while the recovery fishery had the worst performance. When M varied through ages, von-Bertalanffy growth function (VBGF) was introduced into the SCA model to estimate the age-dependent M, and the one-way trip and good contrast fisheries obtained more viable estimated Ms than the recovery and status quo fisheries. The method was also applied to the published data of North Atlantic albacore (Thunnus alalunga), and the estimated M was 0.186 year⁻¹, which was lower than previously assumed (0.3 year⁻¹) and may be viable in view of the high fishing effort imposed on the species.     

Verifier of the maximum sustainable yield estimates of the southern Atlantic albacore,Thunnus alalunga,stock

Maximum sustainable yield (MSY) has generally been accepted as one of the target biological reference points. Albacore, Thunnus alalunga Bonnaterre, is a temperate tuna species widely distributed in marine waters. The International Commission for the Conservation of Atlantic Tunas (ICCAT) and the International Seafood Sustainability Foundation (ISSF) had reported the southern Atlantic albacore stock status with different MSY reference points. In addition, the European Commission's Advisory Committee on Fisheries and Aquaculture (ACFA), on 15 September 2006, proposed to amend the Common Fisheries Policy according to the MSY principle, but there is little information on the verifier of the MSY estimates of this albacore stock. This study verifies the MSY estimates of this albacore (T. alalunga) stock to support the management (i.e. setting of MSY) for the southern Atlantic albacore (T. alalunga) stock. The MSY estimates of the albacore stock were evaluated and verified by different models (i.e. Bayesian surplus production model [BSPM], continuous time delay‐difference model [CD‐DM] and Fox surplus production model [SPM]). The MSY estimates from BSPM and CD‐DM were lower than those from conventional estimates; the relative biomass ratio (B₂₀₁₁/B_MSY) and relative fishing mortality ratio (F₂₀₁₁/F_MSY) from BSPM and CD‐DM were higher than those from ICCAT, which showed that measures should be taken for the sustainable utilisation of this fish stock.     

Pharmacokinetic model of florfenicol in turbot (Scophthalmus maximus): establishment of optimal dosage and administration in medicated feed

The pharmacokinetics of florfenicol (FF) in turbot (Scophthalmus maximus) was studied after single intravenous (10 mg kg⁻¹) and oral (100 mg kg⁻¹) administration. The plasma concentration–time data of florfenicol were described by an open one‐compartment model. The elimination half‐life (t_1/2) was estimated to be 21.0 h, and the total body clearance, Cl, was determined as 0.028 L kg h⁻¹. The apparent volume distribution (V_d) was calculated to be 0.86 L kg⁻¹ and the mean residence time (MRT_iv) was 30.2 h. Following oral administration, the maximum plasma concentration (C_max) of 55.4 μg mL⁻¹ was reached at 12 h (T_max). The absorption constant (k_a) was 0.158 h⁻¹. The bioavailability was estimated to be 57.1%. The low bioavailability observed at higher doses was explained by the saturation of the mechanisms of absorption. The drug absorption process was limited by its inherent low solubility, which limited the amount of available FF absorbed in the gastrointestinal tract. Based on the pharmacokinetic data, an optimal dosing schedule for FF administration is hereby provided. Based on the minimum inhibitory concentration found for susceptible strains of Aeromonas salmonicida, oral FF administration of first, an initial dose of 30 mg FF kg⁻¹, followed by 6 maintenance doses at 18 mg kg⁻¹/daily could be effective against furunculosis in turbot.