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.     

基于物质平衡原理的贝类循环水养殖系统的设计与试验

为恢复和保护濒危淡水贝类资源,该文根据物质平衡原理,以具有代表性的淡水彩虹贝类为研究对象,设计并构建了一套小型的室内淡水彩虹贝循环水养殖系统,该系统由养殖池、生物过滤器、蓄水池、循环水泵、充氧系统和自动投饵装置等环节组成。并在该循环水系统中对钩介幼虫2日龄的彩虹贝幼贝进行了为期60 d的养殖(2011年6月21日到2011年8月20日),整个养殖周期内,彩虹贝幼贝养殖系统环境稳定,水质稳定良好,彩虹贝幼贝壳长日增长量为15.2μm/d,彩虹贝幼贝的最大相对增长率发生在第40天到第50天,其相对生长率为32.4%,和之前池塘流水、跑道式等养殖模式相比,该循环水系统养殖的彩虹贝幼贝获得了更高的生长率。该研究可为淡水贝类的人工繁育和养殖提供参考。     

Acute and chronic toxicity of nitrate to fat greenling (Hexagrammos otakii) juveniles

We evaluated the acute and chronic toxicity of nitrate to juvenile fat greenling Hexagrammos otakii. The 24‐, 48‐, 72‐, and 96‐hr LC₅₀s of nitrate to 1.91 ± 0.7 g greenlings were 2,741, 2,413.5, 2,357.6, or 2,339.2 mg/L nitrate‐N, respectively. Greenlings (6.55 ± 1.83 g) were exposed to 5 mg/L (control) and 157 mg/L for 4 weeks in a recirculating aquaculture system. After 4 weeks, length, weight, feed conversion ratio, and specific growth rate were significantly (p < 0.05) lower for nitrate‐exposed fish than for control fish. Elevated nitrate exposure was associated with decreased plasma hemoglobin concentration and red blood cell count. Our results demonstrate that nitrate poses a threat to greenlings and provide information that is useful for establishing water quality criteria for early life stages of this cultured fish. The sensitivity of greenlings to elevated NO₃^? should be evaluated at other life stages to determine how chronic exposure might impact survival, growth, health, reproductive success, and harvest quality.     

Global population genetic structure of the sequential hermaphrodite,dusky grouper (Epinephelus marginatus)

1. The dusky grouper Epinephelus marginatus is a large epinephelid species that occurs in the eastern and south-western Atlantic and western Indian Oceans. Late maturity, protogynous hermaphroditism, site fidelity, and overfishing have all contributed to its demographic decline.
2. Connectivity and demography within a broad sampling of dusky grouper populations throughout its distribution were assessed. To do so, genetic variation at 11 polymorphic microsatellite loci and a partial sequence of the mitochondrial control region (mtCR) were evaluated.
3. Two major mtCR lineages with a sequence divergence of 1.6% were found. The magnitude of genetic differentiation for mtCR among north and south Atlantic and Indian Ocean populations was high, with Φ_ST = 0.528.
4. D_EST and results of discriminant analysis of principal component revealed significant microsatellite genetic differentiation between all collection areas. Significant pairwise D_EST showed moderate (0.084) to very great (0.603) differentiation. The effective population size was low for all localities, ranging between 25 (Azores Archipelago) and 311 (Rio Grande do Sul). The overall effective population size was estimated as 299 (confidence interval = 215–412), and there was no evidence of strong or recent bottleneck effects.
5. Local and regional genetic structuring among dusky grouper populations is the consequence of the species' site fidelity, distribution across multiple oceanographic boundaries, and probably also of sequential hermaphroditism that contributes to the intensity of random genetic drift.
6. The spatial pattern of genetic structuring of dusky groupers is such that fisheries management and conservation of population genetic integrity will have to be pursued at the local and regional scales.

     

Efficacy of a pilot-scale wastewater treatment plant upon a commercial aquaculture effluent: I. Solids and carbonaceous compounds

A pilot-scale wastewater treatment station was built and operated at a commercial recirculating aquaculture facility in order to initiate, characterize and optimize the operation of a treatment strategy for effluent recovery and reuse. The treatment train consisted of sedimentation, denitrification, ozonation, trickling filter treatment, and chemical flocculation. The study consisted of four different sets of treatment conditions, differentiated by alternative use of 6 or 4 lpm flow and recycling rates, ozone doses between 36.6 and 82.5 mg O₃/l water, and 6- or 9-min ozonation time. The effects of treatment on solids and dissolved organic compounds are reported here. Over 70% of solids were removed by sedimentation under all experimental conditions. At the end of treatment, up to 99% of TSS was removed due to the combined action of ozonation and chemical flocculation. COD removal was not significantly different among experimental conditions by sedimentation (59.2–62.7%, p > 0.05), but was positively correlated with ozone dose (slope = 0.452, r² = 0.99), yielding total COD removal η(CODt) of 19.8–40.7%. Of these amounts, 60.4–66.5% of COD was removed with foam, while the balance was mineralized. The ozone reactivity was 83.7% at a dose of 82.5 mg O₃/l water. The ozone consumption coefficient Y(O₃/CODox) for COD oxidized was 1.92–2.23 g/g O₃ COD and 0.70–0.78 g O₃/g COD when total COD removed was considered. Overall, 87.9–92.4% of COD was removed by the treatment train, to an average of 44 mg/l at the highest ozone dose, a value 3.3–3.9 times less than in fish tanks. Under the same conditions, cBOD₅ was reduced by 88%, 3.8–4.1 times less than in fish tanks. The water’s biodegradability was increased by over 20%. DOC did not change significantly through the treatment train, and fluctuated through the system due to methanol addition to support denitrification. Work with the pilot station showed that the treatment strategy employed could support effective recovery and recycling of aquaculture effluent, although salts and refractory organics may accumulate in the system.     

A novel computer simulation model for design and management of re-circulating aquaculture systems

The aim of this study was to develop a simulation model for finding the optimal layout and management regime for a re-circulating aquaculture system (RAS). The work plan involved: (1) quantifying the effects of fish growth and management practices on production; (2) developing a mathematical simulation model for the RAS, taking into account all factors that directly influence system profitability; and (3) estimating the production costs and, hence, the profitability of an RAS. The resulting model is process-oriented, following the flow of fish through the RAS facility, and generates an animated graphic representation of the processes through which the fish passes as it progress through the system. The simulation assesses the performance in terms of yearly turnover, stocking density, tank utilization and biomass in process, and uses statistics to track the state of the RAS and record changes that affect efficiency. The economic impact of system design and operation was modeled to enable a user to anticipate how changes in design or operating practices, costs of inputs, or price of products affect system profitability. The proposed approach overcomes difficulties in characterizing RAS design and operation. The simulation approach allows all of the RAS's components such as equipment, biological processes (e.g., fish growth), and management practices to be evaluated jointly, so that an initial design can be fine-tuned to produce an optimized system and management regime suited to a specific fish farm within a reasonable time. The methodology was executed step-by-step to design an optimal RAS that meets both economic and stocking-density limits. Optimal design specifications were presented for several case studies based on data from Kibbutz Sde Eliahu's RAS, in which Nile tilapia (Oreochromis niloticus) are raised in 20 concrete raceways. Further research should include more extensive testing and validation of the integrated model, which then should be disseminated to the aquaculture community.     

Metagenomic analysis shows diverse,distinct bacterial communities in biofilters among different marine recirculating aquaculture systems

While biofilters are widely used to metabolize ammonia and other metabolic waste products in recirculating aquaculture systems, their microbial communities are not thoroughly characterized. While inroads have been made characterizing microbial communities within single biofilters, replicated comparisons across biofilters and facilities have been lacking. We hypothesized that microbial communities might differ among filter types and facilities. We characterized and compared the bacterial communities of nine nitrification biofilters in five commercial recirculating marine aquaculture operations by amplifying and sequencing the 16S rRNA gene using the Illumina-MiSeq DNA sequencing platform. Our results demonstrated the usefulness of the approach for elucidating bacterial community structure in aquaculture biofilters; among almost 249,000 usable DNA sequence reads—a mean of 27,663 for each biofilter—we detected a mean of 682 operational taxonomic units. Higher species diversity was observed in the submerged biofilters at farms 3 and 4 (HF_SB1, HF_SB2, HF_SB3, MB_SB1, MB_SB2, and MB_SB3), and a bead filter at farm 2 (XYF-MBBR) than in a bead filter at farm 1 (DF_MBBR) and a fluidized sand filter at farm 5 (TY_FSF). At the phylum level, Proteobacteria were the most frequently observed taxa (representing 36–50 % of reads in the overall data set for a given filter); other frequently observed phyla were Bacteroidetes (13–34 %), Chloroflexi (2–23 %), Nitrospirae (1–7 %), Planctomycetes (1–4 %), and Actinobacteria (2–5 %). However, in fluidized sand filters, after Proteobacteria, the subdominant phyla were Bacteroidetes (19 %), Nitrospirae (17 %), and Planctomycetes (11 %). At the genus level, the nitrite-oxidizing genus Nitrospira was frequently observed in sand filter TY_FSF (16.4 %), bead filter DF_MBBR (7.6 %), submerged biofilter MB_SB1 (7 %), and bead filter XHF_MBBR (7.36), and less frequently in submerged biofilters HF_SB3 (1.94), HF_SB2 (1.77 %), and HF_SB1 (1.63 %), and bead filters MB_SB2 (0.8 %) and MB_SB1 (0.2 %). Observations of the ammonia-oxidizing genus Nitrosomonas varied widely within and among filter types, ranging from 0.06 % in submerged bed filter HF_SB3 to 2.82 % in bead filter DF_MBBR. Principal components and cluster analyses classified the bacterial communities in the nine biofilters into groups corresponding to the respective recirculating marine aquaculture operations and the associated filter types.     

Assessment of AquaMats for removing ammonia in intensive commercial Pacific white shrimp Litopenaeus vannamei aquaculture systems

AquaMats are high surface–area polymer filters whose use produces higher yields with reduced health risks for the aquaculture product. We used AquaMats in pilot-scale systems and in intensive commercial Pacific white shrimp Litopenaeus vannamei production systems to stabilize and improve water quality by removing ammonia. In the pilot-scale systems, evaluation of the effects of temperature and hydraulic retention time (HRT) on ammonia removal rate indicated that the surface total ammonia nitrogen (TAN) conversion rate (STR, mg TAN/m²-day) increased with increasing temperature and decreasing HRT. The highest STR of 319.8 mg TAN/m²-day was observed at a temperature of 30 °C and a HRT of 5 min. In the commercial shrimp production systems, ammonia levels were significantly greater in the control systems (without AquaMats) than in the treatment systems (with AquaMats) after 6 days (P < 0.05). Results suggested that eight 150 cm × 90 cm pieces of AquaMats (0.057 m² surface area per m³ culture volume) were sufficient for promoting nitrification in this system. The growth rate of juvenile shrimp was most enhanced in treatment C (with 12 pieces of AquaMats, 0.085 m²/m³), which exhibited a significant decrease in ammonia.     

Toward Coordination and Funding of Long-Term Genetic Improvement Programs for Striped and Hybrid Bass Morone sp.

The productivity and profitability of striped and hybrid bass Morone sp. aquaculture would be enhanced by genetic improvement of cultured stocks. To date, genetic improvement of cultured bass stocks largely has been limited to interspecific hybridization and ploidy manipulation, techniques which are aimed at short-term genetic gains. Upon domestication, long-term improvement of striped or hybrid bass can be approached. Lines of striped bass and other Morone species can be selected for rapid growth, stress tolerance, disease resistance, combining ability, or other traits. Improved lines can be crossed to produce superior hybrids or crossbreds, or manipulated to produce superior triploid or transgenic stocks. Current breeding projects are limited in size, and coordination of breeding activities among groups would be advantageous. Faced with the likelihood of limited government funding, long-term genetic improvement of Morone species might be supported by the industry through a fund receiving a small percentage of the proceeds from sales of cultured Morone products.