Molecular characterization and expression of the Prostaglandin reductase 1 gene and protein during ovarian development of the giant tiger shrimp Penaeus monodon

Prostaglandin reductase 1 (PTGR1; also called NADP⁺-dependent leukotriene B4 12-hydroxydehydrogenase, LTB4DH) is the key enzyme responsible for biological inactivation of prostaglandins and related eicosanoids. In this study, the full-length cDNA of PTGR1 in the giant tiger shrimp (Penaeus monodon) was characterized. PmPTGR1 was 2405 bp in length with an ORF of 1035 bp encoding a polypeptide of 344 amino acids. Interestingly, its 3′ UTR contained the nucleotide sequence (825 bp) that significantly matched positions 3–277 (with 4 amino acid variants) of the deduced P. monodon peritrophin2 protein. PmPTGR1 was more preferentially expressed in ovaries than testes of P. monodon broodstock. In intact broodstock, PmPTGR1 was up-regulated in early cortical rod (stage III) ovaries (P < 0.05) and comparably expressed afterwards (P > 0.05). In eyestalk-ablated broodstock, PmPTGR1 was temporally lower in early cortical rod compared to previtellogenic (I) and vitellogenic (II) ovaries (P < 0.05) and returned to the previous level in mature (IV) ovaries (P < 0.05). More importantly, the relative expression level of PmPTGR1 in each ovarian stage in eyestalk-ablated females was lower than that in intact P. monodon broodstock (P < 0.05). This strongly suggested that eyestalk ablation potentially affects the expression of PmPTGR1 allowing the stimulating effects of prostaglandins and related eicosanoids on vitellogenesis and ovarian maturation of P. monodon. The level of ovarian PmPTGR1 protein seemed to increase during ovarian development in intact broodstock but slightly reduced in mature ovaries in eyestalk-ablated broodstock. Results suggested the possible contribution of PmPTGR1 in ovarian development of P. monodon.     

Comparison of immune responses and antioxidant status of different generations of growth‐selected Portunus trituberculatus families

The purpose of this study was to investigate the effects of inbreeding on the immune responses and antioxidant status of Portunus trituberculatus juveniles. Results showed that inbreeding affected the total haemocyte count, and phagocytic, pro‐phenoloxidase (propo), phenoloxidase and antibacterial activities decreased after the seventh generation. Antioxidant status showed a similar pattern: total antioxidant capacity, superoxide dismutase (SOD) activity and GSH/GSSG in the cell‐free haemolymph and hepatopancreas decreased, while catalase activity in the cell‐free haemolymph increased (P < 0.05). There were no significant differences in α₂‐macroglobulin and bacteriolytic activities in the cell‐free haemolymph and glutathione peroxidase activity in the cell‐free haemolymph and hepatopancreas among nine inbreeding generations. Gene expression levels of proPO and crustin in haemocytes and SOD in haemocytes and hepatopancreas also decreased significantly as the inbreeding generations increased. The results suggest that a high level of inbreeding could severely reduce the physiological health of P. trituberculatus. Our obtained data would be particularly useful for P. trituberculatus breeding programmes.     

Quantification by fluorescent in situ hybridization of bacteria associated with Litopenaeus vannamei larvae in Mexican shrimp hatchery

The bacterial composition in the hatchery at Unidad Experimental Peñasco (UEP) of the Sonora University, Mexico, was studied by using Fluorescent In Situ Hybridization (FISH) with rRNA-specific oligonucleotide probes. We applied fluorochrome-labeled polyribonucleotide probes to identify and enumerate marine shrimp culture hatchery related bacteria. Quantitative whole-cell hybridization experiments using α-, γ- and δ-Proteobacteria, and high and low G + C Gram-positive bacteria accounted for 20.8 ± 3.4% to 69.3 ± 3.3% of the total 4′,6-diamidino-2-phenylindole (DAPI)-stained cells in most samples. As predicted in a previous study, marine high G + C and γ-Proteobacteria predominated in different shrimp life sub-stages. The elevated percent of high G + C and γ-Proteobacteria, extending from nauplii to mysis stages, suggest that they represent a large and significant fraction of the total picoplankton biomass in Litopenaeus vannamei larval culture.     

Spawning per recruit analysis of the pelagic thresher shark,Alopias pelagicus,in the eastern Taiwan waters

The pelagic thresher shark, Alopias pelagicus, is a cosmopolitan species and abundant in Taiwan waters. Some of its biological information has been documented yet its population dynamics are poorly known. The purpose of this study is to assess the pelagic thresher shark stock status in the eastern Taiwan waters. The whole weights (W) of 51,748 individuals of the pelagic thresher shark landed at Nanfanao and Chengkung fish markets, eastern Taiwan from 1990 to 2004 were converted to precaudal length (PCL) based on the W–PCL relationship (W = 2.25 × 10⁻⁴ × PCL^2.533, n = 2165). The sexes combined VBGE L_t = 189.5 × (1 − e^{−0.10(t+6.47)}) was used to estimate the age for each length group. Total mortality rates (Z) obtained with length-converted catch curves ranged from 0.208 to 0.277 year⁻¹. Natural mortality rate (M) estimated from Hoenig method was 0.132 year⁻¹, and exploitation rate (E) ranged from 0.069 to 0.127 for 1990–2004. Annual abundance was estimated to range from 97,551 in 2000 to 153,331 in 2003 from virtual population analysis, and the highest fishing mortality occurred in ages 8–18 years. There were four different scenarios being simulated in this study. Scenario 1 indicated that spawning per recruit (SPR) ranged from 23.07% in 2001 to 47.71% in 1990 with a mean of 36.41% for the period of 1990–2004. The mean SPR of pelagic thresher for 1990–2004 was below the BRP of SPR = 35% in scenarios 2–4 suggesting that this stock was slightly overexploited. Therefore, to ensure sustainable utilization of this stock, reduction of fishing effort and close monitoring on A. pelagicus are needed.     

Optimization of the lighting system for a Hydraulically Integrated Serial Turbidostat Algal Reactor (HISTAR): Economic implications

An estimated 28% of the production cost in HISTAR systems that are artificially illuminated is attributed to the lighting cost. This cost estimated is based on an operational configuration comprised of eight CFSTRs, a system dilution rate (D_s) of 0.640 d^?1, and 400 W metal halide lamps positioned at an elevation of 38.1 cm over the culture. Deterministic model simulations of the volumetric productivity (P_v), photosynthetic efficiency (E_o) and lighting cost (LC) under various management strategies, operational parameters and reactor design configurations were performed and compared to the simulation results obtained for the original configuration. The simulations showed that LC may be reduced by 35.5% by switching from a metal halide (MH) to high-pressure sodium (HPS) light source at an optimum system dilution rate D_s = 0.641 d^?1. LC may be reduced by an additional 17.8% through decreasing the lamp elevation to 25.4 cm. Increasing the wattage of the light source from 400 to 1000 W in the last six reactors would reduce the LC by 13% from the original cost. Overall, using HPS lamps at 25.4 cm height, with six 1000 W and two 400 W lamps at a D_s = 0.641 d^?1 will result in a 54% overall LC reduction compared to the original configuration of HISTAR. This represents a 13% reduction in the overall microalgal production cost for HISTAR.     

Experimental investigation on the transport of different fish species in a jet fish pump

A jet fish pump with a throat of ø60 mm was designed to study its performance in the transport of different fish species and the physiological changes in fish thereafter. Experiments were conducted to investigate the fish transport rate and energy required to transport each ton of fish when transporting Carassius auratus, commonly known as the Chinese goldfish, Megalobrama amblycephala, or Wuchang bream, and Ctenopharyngodon idella, the grass carp. Fish were examined for external injuries as well as for several important enzymes and hormones which are indicators of tissue injury and stress. The results showed that the transport rate for all three species of fish rose dramatically with an increase in the primary stream rate. In this experiment, the transport rates of C. auratus, M. amblycephala and C. idella reached 2357 ± 37.2 kg ∙ h⁻¹, 2888 ± 41.6 kg ∙ h⁻¹, and 2060 ± 40.2 kg ∙ h⁻¹, respectively. However, both injury rate and energy required to transport each ton of fish increased no matter whether the primary stream rate was too low or too high. Considering both transport rate and injury rate, the mean primary stream rate of 80 m³ ∙ h⁻¹ was determined to be the optimal operating condition in this experiment. Fish were stressed and most likely some of their organs were damaged. However, most physiological indexes almost fully recovered after several hours.     

Age and growth estimates of the sharptail mola,Masturus lanceolatus,in waters of eastern Taiwan

The sharptail mola, Masturus lanceolatus, is one of the largest teleost fishes in the world, and can be found in warm temperate and tropical regions worldwide. The increase of sharptail mola catch in the eastern Taiwan in recent years stimulated a concern that increasing exploitation of this species might lead to a decline of the stock. However, biological information of this species is very limited. Hence, this study provides the first information on age and growth of this species in the waters off eastern Taiwan based on 265 specimens (105 females and 160 males) collected from January 2003 to November 2006 at the Nanfanao and Hualien fish markets, eastern Taiwan. The relationships between whole weight (W) and standard length were expressed as: W = 9.98 × 10^?4 SL^2.45 (n = 105, p < 0.01) for females, and W = 3.33 × 10^?4 SL^2.68 (n = 160, p < 0.01) for males. Based on the MIR analysis, growth band pairs (including translucent and opaque bands) in vertebrae formed once a year and were counted up to 23 and 16 for females and males, respectively. Three growth functions, the von Bertalanffy (VBGF), Robertson, and Gompertz, were used to model the observed length at age data. The VBGF had the best fit and predicted an asymptotic length (L_∞) = 262.5 cm SL, growth coefficient (k) = 0.046 yr^?1, age at zero length (t₀) = ?3.350 yr (n = 80, p < 0.01) for females, and L_∞ = 231.0 cm SL, k = 0.059 yr^?1, t₀ = ?1.852 yr (n = 135, p < 0.01) for males. The longevities were estimated to be 105 and 82 yr based on the VBGF for females and males, respectively.     

Deterring coastal birds from roosting on oyster culture gear in eastern New Brunswick,Canada

An ornithological survey was conducted along the eastern coastline of New Brunswick, Canada, where oysters are cultivated in suspension using PVC bags and wire-mesh cages. Thirteen bird species and a variety of unidentified shorebirds were observed roosting on the floating oyster gear. The double-crested cormorant (Phalacrocorax auritus) was the most common species observed (47.6% of all counts), closely followed by herring gulls (Larus argentatus) and common terns (Sterna hirundo) at 18.7% and 13.0%, respectively. Birds were densely aggregated where few cages or bags had been deployed. A gear-type effect was also detected: birds were more abundant on floating cages (mean = 47.9/100 m² of exposed area, S.E. = 5.8) than on floating bags (mean = 32.8/100 m², S.E. = 1.9). The survey was followed by two experiments designed to test the effects of gear modifications on bird abundance and diversity. For bags, results indicated that shallow immersion (～6 cm below surface) and floater instability were effective deterrents to P. auritus, reducing its abundance by a 37-fold factor. For wire-mesh cages, a dented triangular structure mounted on top of floaters was a harassing physical barrier to roosting behaviour, consequently reducing bird abundances to null (or near null) values.     

Dopamine induces transient modulation of the physiological responses of whiteleg shrimp,Litopenaeus vannamei

Levels of glucose, lactate, Na⁺, K⁺, Cl⁻, protein, and oxyhemocyanin in the hemolymph and its osmolality were measured when the whiteleg shrimp (Litopenaeus vanammei; 20 ± 1.5 g), were individually injected with saline or dopamine at 10^− 8, 10^− 7, or 10^− 6 mol shrimp^− 1. Results showed that elevations of hemolymph glucose and lactate occurred at between 2 and 4 h, increases in hemolymph osmolality, Cl⁻, Na⁺, and total protein occurred at 2 h, and a reduction in hemolymph oxyhemocyanin occurred at 4 h after the dopamine injection. All physiological parameters except K⁺ had returned to the control values 8–16 h after receiving the dopamine. The injection of dopamine also significantly decreased the oxyhemocyanin/protein ratio of L. vannamei at 2 h as a result of the elevation of hemolymph protein. These results suggest that stress-inducing dopamine causes a transient period of modulation of energy metabolism, osmoregulation, and a respiratory response in L. vannamei in adapting to an environmental stress.     

Effects of storage duration and storage media on initial and post-eyeing mortality of stored ova of rainbow trout Oncorhynchus mykiss

The effects of storage duration and storage media on the viability of unfertilized eggs of rainbow trout from fertilization to hatching stage was studied. The unfertilized eggs were stored in coelomic fluid and Cortland artificial media buffered with Tris–HCl (C₄H₁₁NO₃–HCl) and Hepes (C₈H₁₈N₂O₄S) at 2–3 °C. These eggs were fertilized after 0 (i.e. control eggs fertilized prior to storage), 2 and 9 days post-stripping using fresh, pooled sperm obtained from 4 to 5 males. According to the results of present study, after 2 days of storage, no significant (p > 0.05) change in survival to eyeing and hatching of eggs stored in coelomic fluid (85.5 ± 4.8%, 80.2 ± 6.3%) and Cortland medium buffered with Hepes (73.3 ± 4.1%,68.1 ± 4%) was observed in comparison to the control (82.6 ± 8%,78.7 ± 7.8%). However, eyeing and hatching survival rates of eggs stored for the same period in Cortland medium buffered with Tris–HCl (44.5 ± 7%,34.2 ± 8.2%) decreased significantly (p < 0.05) in comparison with the control. Also, eggs stored for 2 days in Cortland medium buffered with Tris–HCl (25 ± 6.7%) had significantly (p < 0.05) greater eyed egg mortality compared to the control (4.7 ± 0.6%), while no significant (p > 0.05) differences were observed between eyed egg mortality rates of eggs stored in coelomic fluid (6.7 ± 2.1%) and Cortland medium buffered with Hepes (7.3 ± 0.9%) compared to control. After 9 days of storage, the eggs that were stored in coelomic fluid showed no significant (p > 0.05) differences in eyeing (77.5 ± 7.2%) and hatching (67 ± 8.1%) rates in comparison with control, while both Cortland storage media exhibited significant (p < 0.05) loss in eyeing (44.4 ± 11.5%, 24.7 ± 13.8% for Hepes and Tris–HCl, respectively), and hatching (24.5 ± 5.9%, 19.2 ± 14.4% for Hepes and Tris–HCl, respectively) in comparison with control. Furthermore, eyed egg mortality increased significantly (p < 0.05) in coelomic fluid (14 ± 2.9%), media buffered with Hepes (43 ± 6.2%) and Tris–HCl (49.3 ± 26.9%) compared to control. Based on this study, unfertilized eggs of rainbow trout can be successfully stored in coelomic fluid for 9 days at (2–3 °C) without significant loss of fertility. However, storage within a similar period in artificial media showed lower fertilization rates and higher eyed egg mortality compared to coelomic fluid.     

Topographic preferences and habitat partitioning by pelagic fishes off southern Western Australia

Pelagic fishes are typically considered mobile and wide-ranging open ocean foragers. However, many species have also been recorded in association with nearshore topographic structures. The relative abundance of four pelagic species at and away from topographic features on the continental shelf, as inferred from fine-scale catch data collected over a 7-year period, was examined for southern Western Australia. A total of 1056 captures were recorded from 890 h of trolling over 102 days: the top four species accounted for 97.5% of all captures. Eight distinct topographic features received 13.7% of the total trolling effort and produced 43.8% of captures. The percentage of all captures within 1 km of these features were 80% for yellowtail kingfish (Seriola lalandi, YTK), 50% for bonito (Sarda australia, BON), 27% for southern bluefin tuna (Thunnus maccoyii, SBT), and less than 5% for skipjack tuna (Katsuwonus pelamis, SKJ). Catch rates were 26, 6.59, and 2.47 times higher than catch rates away from the topographic features for YTK, BON, and SBT, respectively. In contrast, SKJ catch rates were 1/3rd lower at topographic features, indicating avoidance rather than preference. The mean distance at which species were captured from the center of each feature differed significantly, with YTK closest (303 m), followed by SBT (442 m), BON (493 m), and SKJ (539 m). These findings indicate habitat partitioning in pelagic fishes at topographic features and offer a way to increase catch of a targeted species, or reduce the capture of unwanted or quota-limited species.     

Population dynamics of Melicertus kerathurus (Decapoda: Penaeidae) in Thermaikos Gulf (N. Aegean Sea)

The east Atlantic-Mediterranean penaeid Melicertus kerathurus constitutes a valuable resource for Mediterranean fisheries. In recent years, its world production is almost totally based on the yields from Greece and Tunisia. A two-year study of prawn stock in Thermaikos Gulf (NW Aegean Sea) provided information on age, growth and mortality of the species. M. kerathurus exhibits a marked sexual growth dimorphism, with females showing an overall wider size range and greater size than males. Mean monthly size, CL_max were also in favor of females. Monthly age classes varied from one to four for females and from one to three for males, and corresponded to three generations (0⁺, 1⁺, 2⁺). New generation (0⁺) cohorts recruited into fishery in waves, from late summer to February. According to the von Bertalanffy growth curve, females grow larger than males, but there is a prominent seasonal growth oscillation in both sexes (females: CL_∞ = 62.48, K = 1.15, C = 0.87, WP = 0.16, Rn = 0.170; males: CL_∞ = 47.78, K = 1.28, C = 0.97, WP = 0.12, Rn = 0.205). Growth performance indices (φ′, φ) and longevity were in favor of females. K values for both sexes in Thermaikos Gulf are the highest reported for the species, suggesting a higher growth rate and a lower longevity. Estimated values for total, natural and fishery mortality were greater in males. In both sexes, an exploitation rate E > 0.5 was found, implying an intense fishing impact on M. kerathurus stock in Thermaikos Gulf. Intense exploitation in other parts of the Mediterranean and eastern Atlantic, along with the replacement of the species by Eritrean penaeid prawns in the eastern Mediterranean, has resulted in a severe reduction in catches, in most countries. Thus, existing stocks of M. kerathurus should be considered as potentially endangered, and species-specific initiatives towards sustainable management of this resource should be implemented.     

The effects of food and the sum of effective temperature on the embryonic development of the seahorse,Hippocampus kuda Bleeker

The effect of different food (live Acetes spp., live Mysis spp., frozen Mysis spp., and mixed food of 50% live Acetes spp. and 50% frozen Mysis spp.) on gonad development of seahorses, Hippocampus kuda Bleeker, was evaluated in this experiment. The developmental durations of testes and ovary of seahorses were significantly different among the four experimental treatments. The live Acetes spp. treatment presented the shortest developmental durations to stage V, which were 87.6 ± 3.84 days and 89.2 ± 3.71 days, respectively, for ovary and testes. The frozen Mysis spp. treatment had the longest developmental durations (F_3,15 = 13.284, P < 0.05). The relationship between developmental duration of the ovary and gonad developmental stages could be formulated: Y₁ = 12.04x + 24.36 (r² = 0.9722, n = 16, P < 0.05). The gonadosomatic index (GSI) of parent seahorses among the four treatments differed significantly (F_3,15 = 18.364, P < 0.05). The standard GSI of seahorses fed live Acetes spp. was 15.64 ± 1.65%, which was the highest. Feeding live food had a significant effect on the fecundity and spawning of seahorses. The fecundity and spawning number of the live Acetes spp. treatment were 598 ± 45.49 and 552 ± 49.19 individuals, respectively, which were dramatically higher than those of frozen treatment (F_3,19 = 34.152, P < 0.05). Live food also had a similar effect on the fertilization and hatching rate during the embryonic development of seahorses (F_3,19 = 11.386, P < 0.05). Food treatment could also induce an indirect effect on survival rate of juveniles through gonadal and embryonic development of the parents (F_3,15 = 14.519, P < 0.05). In this experiment, the mortality within parent seahorses in the frozen Mysis spp. treatment was the highest (15.1 ± 6.55%), and the survival of juveniles was the highest in the live Acetes spp. treatment (90.4 ± 2.26% at 10 days). In conclusion, feeding live Acetes spp. significantly benefited the gonadal and embryonic development of H. kuda.The effect of temperature (22 °C, 24 °C, 26 °C, 28 °C, 30 °C and 32 °C) on the hatching time of H. kuda was also studied. We demonstrated that the higher the temperature, the shorter the hatching time, as well as the higher the hatching speed. The relationship between hatching time and temperature could be expressed: T = − 39.337 t + 677.75 (r² = 0.9755, n = 30, P < 0.05). In this finding, we provided the sum of effective temperature (SET) and threshold temperature of embryonic development of H. kuda (14066.9 °C h^− 1 and 13.7 °C, respectively). This new information on the effect of feeding type and culture temperature is beneficial for the commercial rearing and breeding industry of this species.     

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

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

Routine oxygen consumption rates of california halibut (Paralichthys californicus) juveniles under farm-like conditions

Fish oxygen requirement is a fundamental variable of aquaculture system design and management, as it is the basis for determining water flow rates for sustaining stock. A study on oxygen consumption of California halibut (Paralichthys californicus) between 3.2 and 165.6 g was conducted in small raceways (2.41 m long, 0.28 m wide, and 0.22 m high; operational water depth between 0.05 and 0.10 m with a quiescent zone 19 cm long in the effluent section) working as open respirometers in a recirculating system under farm-like conditions. The fish were fed commercial dry pelleted feeds at a ratio of ～0.70–3.00% of body weight (BW) and stocked at densities between 94% and 316% percent coverage area (PCA). Oxygen consumption rates were determined by mass balance calculations. The mean and maximum oxygen consumption rates (g O₂/kg fish/day) for juvenile California halibut under the conditions tested can be expressed by M_day = 15.077W^?0.2452 and M_day = 17.266W^?0.2033, respectively, where W is fish weight in grams. The determination of oxygen consumption by California halibut in farm-like conditions provides valuable information on the oxygen requirement of these fish in an aquacultural setting. This information can be used for designing and sizing a rearing facility for the intensive culture of California halibut.     

Routine oxygen consumption rates of california halibut (Paralichthys californicus) juveniles under farm-like conditions

Fish oxygen requirement is a fundamental variable of aquaculture system design and management, as it is the basis for determining water flow rates for sustaining stock. A study on oxygen consumption of California halibut (Paralichthys californicus) between 3.2 and 165.6 g was conducted in small raceways (2.41 m long, 0.28 m wide, and 0.22 m high; operational water depth between 0.05 and 0.10 m with a quiescent zone 19 cm long in the effluent section) working as open respirometers in a recirculating system under farm-like conditions. The fish were fed commercial dry pelleted feeds at a ratio of ∼0.70–3.00% of body weight (BW) and stocked at densities between 94% and 316% percent coverage area (PCA). Oxygen consumption rates were determined by mass balance calculations. The mean and maximum oxygen consumption rates (g O₂/kg fish/day) for juvenile California halibut under the conditions tested can be expressed by M_day = 15.077W^−0.2452 and M_day = 17.266W^−0.2033, respectively, where W is fish weight in grams. The determination of oxygen consumption by California halibut in farm-like conditions provides valuable information on the oxygen requirement of these fish in an aquacultural setting. This information can be used for designing and sizing a rearing facility for the intensive culture of California halibut.     

Design characteristics of pooled circular stepped cascade aeration system

Aeration experiments were conducted in a brick masonry tank of dimension 4 m × 4 m × 1.5 m to study the design characteristics of pooled circular stepped cascade (PCSC) aeration system. Based on dimensional analysis, non-dimensional numbers related to geometric, dynamic and process parameters were proposed. The non-dimensional geometric parameters – number of steps (N), ratio of total height of cascade (H) to the bottom radius of cascade (R_b), % coverage of circumference of each step by enclosure (P_e) and number of enclosures in each step (N_e) were optimized. Maintaining the optimized geometric parameters (N = 6, H/R_b = 0.25, P_e = 20% and N_e = 9), aeration experiments were further conducted at different discharges (Q) to develop simulation equations for prediction of aeration characteristics of PCSC aeration system at different dynamic conditions. Simulation equations for oxygen transfer and power consumption based on Froude (Fr) criterion were developed subject to 0.0014 ≤ Fr ≤ 0.0144. SAE of the developed prototype PCSC aerators based on estimated brake power ranged between 2.43 and 3.23 kg O₂/kWh.     

Use of vegetated drainage ditches and low-grade weirs for aquaculture effluent mitigation: II. Suspended sediment

Total suspended solids are a priority pollutant under the Clean Water Act and a point of concern for aquaculture facilities. The use of ubiquitous vegetated ditches on the aquaculture landscape may serve as an environmentally and economically sustainable practice for reducing suspended sediment contributions to downstream environments. This study assessed effects of consecutive low-grade weirs on suspended solids retention and settling rates of aquaculture pond effluent in a single drainage ditch. Two control and nine treatment discharges were conducted in September and October 2012 at the Mississippi State University South Farm Aquaculture Facility. All discharges decreased total and volatile suspended solid loads. Total suspended solids were decreased 72–94%, with a significant removal rate of 0.02 ± 0.01 mg L⁻¹ min⁻¹ in both control (F = 6.12, P < 0.001) and treatment discharges (F = 16.02, P < 0.001). Volatile suspended solids comprised 2–80% of total suspended solids and had a significant removal rate of 0.02 ± 0.001 mg L⁻¹ min⁻¹ in both control (F = 10.46, P < 0.001) and treatment discharges (F = 6.28, P < 0.001). There was no significant difference in overall settling rates between control and treatment discharges; however, prior to weir 1, both total and volatile suspended solid concentrations increased in control discharges. Treatment discharges decreased both total and volatile suspended solids significantly (P < 0.001) prior to weir 1. Further analysis revealed flow rate to be a significant (P < 0.001) variable in total suspended solid removal while initial concentrations affected reduction rates of volatile suspended solids significantly (P < 0.001). These results suggest that the use of low-grade weirs could be a viable best management practice that easily integrates within the aquaculture landscape and creates hydraulic conditions conducive to sediment retention.     

The effect of nearly closed RAS on the feed intake and growth of Nile tilapia (Oreochromis niloticus), African catfish (Clarias gariepinus) and European eel (Anguilla anguilla)

One of the challenges that Recirculating Aquaculture Systems (RAS) are still facing is the risk that in RAS fish grow less than in flow-through systems due to the accumulation of substances originating from feed, fish or bacteria associated with the water re-use. The present study investigated whether RAS with high and low accumulation levels of these substances affect feed intake and growth of Nile tilapia Oreochromis niloticus, African catfish Clarias gariepinus, and European eel Anguilla Anguilla. One-hundred and twenty individuals of each species were used (start body weights: Nile tilapia 264.8 ± 8.3 g; African catfish 253.2 ± 2.1 g and European eel 66.6 ± 1.3 g). For a period of 39 days, growth and feed intake were compared between high and low accumulation RAS. HIGH accumulation RAS was designed for maximal accumulation of substances in the water by operating the system at nearly-closed conditions (30 L/kg feed/d), using mature biofilters and high feed loads; and (2) LOW accumulation RAS was designed to be a proxy for flow-through systems by operating at high water exchange rates (1500 L/kg feed/d), new biofilters and low feed load. HIGH accumulation RAS induced a reduction in feed intake (42%) and growth (83%) of Nile tilapia, as compared to systems that are a proxy for flow-through conditions. This effect was not observed in European eel and African catfish. The cause of this reduced feed intake and growth rate of Nile tilapia is still unclear and should be addressed in further studies.     

Short-term hooking mortality of three marine fish species (Sparidae) caught by recreational angling in the south Portugal

Short-term hooking mortality was evaluated for three sparid species [Diplodus vulgaris (Geoffroy Saint-Hilaire), Sparus aurata L. and Spondyliosoma cantharus (L.)] in the Algarve, south Portugal. Fishes were caught from the shore during October 2009 at a fish farm reservoir (Ria Formosa), using three different hook sizes. The relationships between hooking mortality and seven independent variables were analyzed using logistic regression models. In all, 384 fishes representing the three target species were caught during the angling sessions. The most caught species was S. cantharus (n = 181; 100% undersized), followed by S. aurata (n = 137; 89% undersized) and D. vulgaris (n = 66; 97% undersized). Mortalities ranged between 0% for D. vulgaris and 12% for S. aurata (S. cantharus, 3%). For S. aurata, anatomical hooking location was the main predictor of mortality, with 63% of the fishes that died being deeply hooked. Our results support the current mandatory practices of releasing undersized fish for the studied species, given the low post-release mortality rates observed.