Reproductive cycle and plasma levels of steroids in male Eurasian perch Perca fluviatilis

From April 1995 to April 1996, the annual reproductive cycle of male Eurasian perch Perca fluviatilis was studied at the Lindre Center (Moselle, France). At monthly intervals, five males (mean body weight of 133 ± 43 g and total length of 175 ± 9 mm) were caught. From sampled organs, the gonadosomatic (GSI), hepatosomatic (HSI) and viscerosomatic indexes (VSI) were calculated and plasma testosterone (T) and 11-ketotestosterone (11KT) levels were measured. After the spawning period in mid-April, GSI and HSI dropped and VSI increased to 3.8 ± 0.1 %. In September, GSI reached its maximum (8.5 ± 1.8 %). At this time, spermatocytes, spermatids and spermatozoa were abundant, whereas in June only spermatogonia were observed. During winter, GSI was stable at approximately 5 %, HSI reached its maximum (1.9 ± 0.3 %) and VSI was low (2.6 ± 0.2 %). From April to November 1995, plasma T and 11KT concentrations were low (< 0.5 ng·mL^–1). Plasma T levels increased significantly in December and reached peak levels (12.3 ± 2.1 ng·mL^–1) in January, then decreased in February and increased again until spawning in April (6.8 ± 2.1 ng·mL^–1). This second elevation could be related to the beginning of a new spermatogenic cycle. Plasma levels of 11KT increased significantly from October to February 1996 (4.9 ± 1.1 ng·mL^–1). From February to the spawning period (April 1996), plasma 11KT decreased significantly, but values were significantly higher than those measured in fall. Males were spermiating from January to spawning in April.     

A comparative analysis of harvested and unharvested populations of the smooth Venus clam Chionista fluctifraga in the Gulf of California

The shellfishery of the smooth Venus clam Chionista fluctifraga is not regulated in Mexico. Therefore, information on the ecology of this species and the effects of the fishery on its populations is necessary to inform management. We present results from a comparative analysis of the density, biomass, and size structure of smooth Venus clam populations in an area not subjected to harvest (UH) and two areas under harvest (H1 and H2) in Bahía de San Jorge (Gulf of California). The UH population had a density of 20.8?±?1.4 ind m^?2 and a biomass of 392?±?39.7 g m^?2 on average; the size range was 3.1–55.5 mm (average 28?±?15.2 mm), and the predominant size class was 40–50 mm. The H1 and H2 populations had, respectively, densities of 14.5?±?9.5 and 7?±?6.8 ind m^?2 and biomass of 123.4?±?20.4 and 123.6?±?22.6 g m^?2; the size ranges were 2.1–49 and 4.3–48.7 mm (averages 24.5?±?14.3 and 30.1?±?13.2 mm), and the predominant size classes were 0–10 mm and 40–50 mm. Clams in the three populations show an aggregated distribution and live in medium-fine sands (no significant differences in grain size among sites) with oligotrophic water. Although the densities observed in the harvested sites are relatively high, negative effects of the shellfishery are detected. For example, all clam sizes are being harvested, and clams are no longer found in the uppermost zone in harvested sites, with potential impacts on other species. This poses various threats that, together, may decrease the stability of the intertidal ecosystem and affect productivity.

     

Spermiation of paddlefish (Polyodon spathula,Acipenseriformes) stimulated with injection of LHRH analogue and carp pituitary powder

The potential of carp pituitary powder (CPP) at one dose, or the luteinizing hormone-releasing hormone (LH-RH) analogue, des–Gly¹⁰,(d–Ala⁶)–LH-RH–ethylamide, at three different doses to stimulate spermiation in paddlefish (Polyodon spathula) was tested. Single injections of the LH-RH analogue at 0.2, 0.1, or 0.05 mg·kg^–1 increased the number of spermatozoa per kilogram of body weight (kg^–1 b.w.) by 4.7, 3.4, and 3.4 times respectively compared to control, but the number of spermatozoa per kilogram of body weight decreased with CPP (4 mg·kg^–1) by 1.7 times compared to the control. The LH-RH analogue prolonged active spermiation, with numbers of spermatozoa ranging from 7.69 to 1.19 × 10⁹ kg^–1 b.w. up to 96 h after treatment. Analysis of variance showed significant influence of experimental groups on volume of sperm per male and per kilogram of body weight, and the total number of spermatozoa per kilogram of body weight, but insignificant influence on the total number of spermatozoa per male. The percentage of motile spermatozoa was not different between experimental groups for sperm collection at different times after injection. A very high positive correlation (r = 0.93) was obtained between sperm concentration and sperm transmittance measured with a spectrophotometer. This relationship was described with the following linear regression: sperm concentration (× 10⁹ mL^–1) = 1.3244 X^–0.9969, where X is the percentage of sperm transmittance.     

Carrying capacity for finfish aquaculture. Part I—Near-field semi-analytic solutions

The ecosystem carrying capacity for aquaculture cage farming in South Australia is based on guidelines that the maximum feed rates (and farmed fish biomass) be determined such that the concentration c of a given dissolved nutrient does not exceed a prescribed value (say c_P). The problem then is one of relating the nutrient flux F, due to feeding, to the tracer concentration c. To this end the evolution of concentration is modelled using the depth-averaged advection–diffusion equation for a constant source flux F over a finite area cage (or lease) and for both constant and time dependent (tidal) velocities. The divergence theorem is applied to this equation to obtain a new scale estimate of the relation between the flux F and the maximum concentration c_max of a nutrient in the cage region: c_max ≈ F·T*, where T* is a time scale of cage “flushing” that involves both advection and diffusion. The maximum allowed nutrient flux F (and carrying capacity of fish biomass) can then be simply estimated from: F ≈ c_P/T*. New semi-analytic solutions of the advection–diffusion equation for a finite (cage) source are then derived to explore the physics of concentration evolution for constant and tidally varying currents, and to show that the estimate c_max ≈ F·T* is surprisingly robust and generally within 40% of the exact values for a wide set of advective/diffusive parameters. The results generally should find application in other finite source flux problems in the coastal oceans including desalination plants and waste water outfalls.     

Day–night alternation prevails over food availability in synchronising the activity of Piaractus brachypomus (Characidae)

Pirapatinga given submaximal rations grow faster when fed at night than when fed during daylight hours. It was hypothesised that these fish were day–night conformers, with a nocturnal acrophase, and expended more energy during daytime feeding. In order to test this hypothesis, telemetry was applied to study the behaviour of cultured pirapatinga (stocking biomass of 40 kg·m^–3; 27 ± 1 °C; 6 mg O₂·L^–1; 13.5 L/10.5 D) under three feeding schedules (diurnal versus nocturnal feeding [12 g·d^–1·fish^–1 over 10 h] versus fasting) that were evaluated in succession over 1 week each. This implied a feasibility study to test the adequacy of tagging fish with surgically implanted transmitters (ventrolateral incision, posterior to the pelvic girdle). There was no mortality or tag loss over 12 months following surgery, and abdominal incisions healed within 4 weeks. Under all three feeding schedules, activity increased at dawn, peaked during daytime, decreased at twilight and reached a minimum during the late night. Diurnal and twilight activity levels were similar under all three schedules, whereas nocturnal activity was significantly lower with daytime feeding. These observations indicate that pirapatinga have a diurnal activity acrophase, which is little influenced by food availability, and imply that the higher growth of fish fed at night does not originate from lower energetic expenditures.     

Lack of arterial PO<Subscript>2</Subscript> downregulation in Atlantic salmon (<Emphasis Type="Italic">Salmo salar</Emphasis> L.) during long-term normoxia and hyperoxia

Regulation of arterial partial pressure of O₂ (P_aO₂) in Atlantic salmon (Salmo salar) was investigated during resting conditions in normoxic and hyperoxic water. Dorsal aorta cannulated adult Atlantic salmon (1.2–1.6 kg, n = 8) were exposed to 2 week sequential periods of normoxia [16.7 ± 1.1 kPa (mean ± SD)] and hyperoxia (34.1 ± 4.9 kPa) in individual tanks containing seawater (33.7 ± 0.2 ppt) at stable temperature conditions (8.7 ± 0.7°C) and a light regime of L:D = 12:12. Tank design and sampling procedures were optimized to provide suitable shelter and current for the fish, and to allow repeated, undisturbed sampling of blood from free-swimming fish. Fish were sampled regularly through the experimental period. P_wO₂, P_aO₂, blood ion composition (Na⁺, K⁺, Cl⁻), acid–base status (pH, PCO₂, HCO₃ ⁻), haematocrit and glucose were measured. The most frequently observed P_aO₂ values were in the range of 60–80% of P_wO₂, both during normoxia and hyperoxia, and P_aO₂ values were significantly lower during normoxia than during hyperoxia. Blood pH, PCO₂ and HCO₃ ⁻ were significantly elevated during hyperoxia, while, Na⁺, Cl⁻ and Hct were significantly lower. K⁺ and glucose showed no significant differences. This study demonstrates a lack P_aO₂ regulation in Atlantic salmon to low partial pressures, in contrast to previous reports for many aquatic gill breathing animals. Both during normoxia and hyperoxia, P_aO₂ reflects P_wO₂, and alterations in external PO₂ consequently result in proportional arterial PO₂ changes. Physiological adaptation to hyperoxia, as illustrated by changes in several blood parameters, does not include down-regulation of P_aO₂ in Atlantic salmon. The lack of P_aO₂ regulation may make Atlantic salmon vulnerable to the oxidative stress caused by increased free radical formation in hyperoxic conditions.     

Effects of altered photoperiod regimes during winter on growth and gonadosomatic index in Arctic charr (Salvelinus alpinus) reared in freshwater

The short‐ and long‐term effects of altered photoperiods during winter on growth and final gonadosomatic index (GSI) were investigated in 178 individually tagged 2‐year‐old smolt Arctic charr from an anadromous strain. The fish were reared at ambient temperature (2.3–12.5°C) for 18 months and reared at five different photoperiods. One group was reared on constant LD16:8 (light–dark, N = 40) photoperiod and a second group on continuous light (LD24:0, N = 32) throughout the experimental period. Three groups of fish were moved from LD16:8 to LD24:0 for 44 days and subsequently back to LD16:8, that is early winter light group (Early WL: 17 November–5 January; N = 35), Mid WL group (5 January–23 February; N = 38) and Late WL group (23 February–6 April; N = 33). No differences in growth were found for females, whereas males reared at constant LD24:0 were larger (mean ± SEM, 1,780 g ± 180) compared with the Late (1,264 g ± 101) and Mid WL (1,413 g ± 120) groups towards the end the study. Exposure to continuous light during early winter significantly influenced the GSI in female Arctic charr, whereas no differences were found in the males. Female GSI (%) was lowest in the Mid WL group (1.7) and highest in the LD24:0 group (7.0). In conclusion, the present study demonstrated that application of brief continuous light treatments during January and February can possibly be used as a tool to lower subsequent female maturation in Arctic charr farming.     

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.     

Recruitment and movement of the hard clam Meretrix lusoria in a tidal river of northern Kyushu,Japan

Size-frequency distributions of Meretrix lusoria, a commercially important bivalve in Japan, were compared among 6 sites in tidal flats of a small river in Kafuri Bay, northern Kyushu, Japan during 2006–2008. In Kafuri Bay, the hard clam resource is strictly managed and mean biomass of this species on the fishing ground (about 1.5 km²) exceeded 1.5 kg m^?2 in 2008. Small clams (<5 mm in shell length, SL) were most abundant in the border area between the river and the sea, while large clams (>40 mm SL) were rare there. In contrast, in the lower site of the marine area (site L), most clams were >30 mm SL. These results indicate that small clams move from riverine to marine areas with growth (post-settlement movement). Year-round, very small clams (<1 mm SL) were present and clams that were 2–5 mm SL were very rare, although the spawning season is thought to occur in summer. Probably, the early growth of many new recruits is very slow and most may even be <1 mm SL in the next spring, although some clams grow to >5 mm SL in a short period of time.     

Effects of dietary administration of Macsumsuk® on growth and stress to low salinity and low dissolved oxygen in whiteleg shrimp,Litopenaeus vannamei (Boone, 1931) juveniles

An 8‐week study was conducted to explore the results of Macsumsuk^® as a feed additive on the stress tolerance and growth of Litopenaeus vannamei in 15 culture tanks of 36 L each. Three hundred shrimp averaging 0.1 ± 0.01 g were fed with five isonitrogenous (48.38 ± 0.38% CP) diets (in triplicate groups) containing kaolinite (Macsumsuk^®) at 0%, 0.3%, 0.6%, 1.2% and 2.4%, namely Mk₀, Mk_0.3, Mk_0.6, Mk_1.2 and Mk_2.4. Specific growth rate (SGR) and weight gain (WG) of shrimp fed diets Mk_1.2 and Mk_2.4 were significantly better than those of shrimp fed diet Mk₀ (p < .05). However, SGR and WG of shrimp fed diets Mk_0.6, Mk_1.2 and Mk_2.4 were not significantly different. Protein efficiency ratio (PER) and feed efficiency (FE) of shrimp fed diets Mk_1.2 and Mk_2.4 were significantly better than those of shrimp fed diets Mk₀, Mk₀.₃ and Mk_0.6. Furthermore, the survival of shrimp fed diet Mk_2.4 was significantly lower than that of shrimp fed diet Mk_0.6 (p < .05). Cumulative mortality of shrimp fed diet Mk_1.2 was significantly lower than that of shrimp fed diet Mk₀ at 1–1.5 hr post‐stress to low dissolved oxygen (from 6.1 mg/L to 2.9 mg/L) and 4–5 hr post‐stress to low salinity (from 32‰ to 1‰) (p < .05). The optimum dietary Macsumsuk^® level for juvenile L. vannamei was determined as 1.97% by the polynomial regression analysis of weight gain.     

Effects of dietary fermented by‐product of mushroom,Pleurotus ostreatus,as an additive on growth,serological characteristics and nonspecific immune responses in juvenile Amur catfish,Silurus asotus

The present experiment was conducted to evaluate the efficacy of dietary fermented by‐product of mushroom, Pleurotus ostreatus, (FBPM) as an additive in juvenile Amur catfish, Silurus asotus. Five diets were formulated to contain 0%, 0.1%, 0.2%, 0.4% and 0.8% (FBPM₀, FBPM_0.1, FBPM_0.2, FBPM_0.4 and FBPM_0.8 respectively) of FBPM. Fifteen fish averaging 5.7 ± 0.1 g (Mean ± SD) were fed one of the five diets in triplicate groups at 3–4% of wet body weight/day for 8 weeks. Average weight gain (WG) and specific growth rate (SGR) of fish fed FBPM_0.1 and FBPM_0.2 diets were significantly higher than those of fish fed FBPM₀. Hematocrit contents of fish fed FBPM_0.2 were significantly higher than that of fish fed FBPM₀. Lysozyme activity of fish fed FBPM_0.1 was significantly higher than those of fish fed FBPM₀, FBPM_0.2, FBPM_0.4 and FBPM_0.8, while chemiluminescent (CL) responses of fish fed FBPM_0.2 was significantly higher than those of fish fed FBPM₀, FBPM_0.1, FBPM_0.4 and FBPM_0.8. Broken line regression analysis of WG showed that optimum dietary FBPM levels based on WG could be 0.11%. Therefore, these results suggested that the optimum dietary inclusion level of mushroom, Pleurotus ostreatus by‐product fermented using lactobacillus and yeast could be greater than 0.11% but less than 0.2% based on WG and immunological responses in Amur catfish, Silurus asotus without any adverse effects on serological characteristics and body composition.     

Determination of grapefruit (Citrus paradisi) peel extract bio‐active substances and its application in Caspian white fish (Rutilus frisii kutum) diet: Growth,haemato‐biochemical parameters and intestinal morphology

In this study, total phenolic and flavonoid contents of grapefruit peel extract (GPE) were equal to 117.3 ± 0.3 µg of gallic acid/mg and 39.30 ± 0.1 µg of quercetin/mg respectively. Caspian white fish (n = 180, 4 ± 0.9 g body weight) was fed with supplemented diets, including 0, 6.25, 12.5 and 25 mg of GPE/kg for 60 days at 25 ± 1°C. The growth performance was markedly improved in fish fed with 25 mg/kg of GPE compared to others (p < 0.05). Moreover, fish fed with 25 mg/kg of GPE showed a significant increase in red blood cell (2.65·10⁶ cell/mm³), white blood cell (17.75·10³ cell/mm³), packed cell volume (48%) and haemoglobin concentrations (8.75 g/dl) compared to the control (p < 0.05). However, the highest alanine aminotransferase (140 U/L), alanine transaminase (14.5 U/L), and alkaline phosphatase (18.5 U/L) were observed in control group. Morphological analysis of intestine revealed the highest amount of villus width (8.4 µM), height (32.86 µM) and surface area (342.7 µM²) in fish fed with 25 mg/kg of GPE (p < 0.05). In conclusion, supplementing feed with GPE at 25 g/kg can improve growth performance and haemato‐biochemical parameters of Caspian white fish fry.     

Contribution of the symbiotic dinoflagellate Symbiodinium microadriaticum to the nutrition,growth and survival of larval and juvenile tridacnid clams

The role of the symbiotic alga Symbiodinium microadriaticum (= zooxanthellae) in growth, development, and survival of larval and juvenile tridacnid clams was investigated. The zooxanthellae were not present in eggs released from adult Tridacna gigas and Hippopus hippopus, but were ingested by veliger larvae after development from the trochophore stage. Growth of veligers of the clam H. hippopus fed freshly-isolated S. microadriaticum was significantly higher than the growth of starved veligers. In contrast, veligers fed cultured strains of S. microadriaticum and 1–5-day-old isolates of S. microadriaticum from H. hippopus had growth and survival rates not significantly different from starved veligers. These results suggest that translocated photosynthetically-fixed carbon from the ingested freshly-isolated algae was responsible for increased veliger growth and survival.The presence of zooxanthellae in the stomachs of veligers before metamorphosis facilitated establishment of a symbiosis with S. microadriaticum and a concurrent increase in growth after metamorphosis. The establishment of the symbiosis with S. microadriaticum entailed passage of the algae from the stomach, through the digestive gland, and into the developing haemal sinuses. The contribution of photosynthetically-fixed carbon from the symbiotic zooxanthellae could theoretically account for the respiratory demand of 6-week-old juveniles of H. hippopus, corroborating positive growth of unfed symbiotic juvenile clams maintained in filtered seawater.When offered a variety of free-living and symbiotic species of algae, juvenile H. hippopus established a symbiosis only with strains of S. microadriaticum. Other species of algae were apparently digested if small enough to be ingested. Less than 7% of the free-living phytoplankton species Isochrysis galbana and Platymonas subcordiformis that were ingested by symbiotic juvenile Tridacna gigas (3–12 months old) were passed intact through the digestive system after 3 days. In contrast, when freshly-isolated zooxanthellae from T. gigas were offered to symbiotic juvenile T. gigas, up to 76% of the zooxanthellae ingested passed through the clam's digestive system and were released in faecal pellets intact. The symbiotic dinoflagellate Amphidinium klebsii and the diatom Phaeodactylum tricornutum were not ingested by veliger or juvenile clams.     

Leaching properties of three different micropaticulate diets and preference of the diets in cod (Gadus morhua L.) larvae

Leakage of water soluble nutrients from larval microparticulated feeds is probably extensive and needs to be further investigated. Leaching rates of ¹⁴C-labelled serine, pepsin hydrolysed, protein enriched ¹⁴C-algae extract and intact protein enriched ¹⁴C-algae extract were measured from three microparticulated feeds for marine fish larvae (heat coagulated, protein bond feed; agglomerated feed; protein encapsulated feed). The effects of particle size (< 0.3 mm, 0.3–0.6 mm; 0.6–1.0 mm) and immersion time (1–60 min) in salt water were also tested. Leaching increased by decreasing molecular weight of leaching component (P < 10^− 5), by the feeds in order encapsulated, heat coagulated and agglomerated feeds (P < 10^− 5), by longer immersion time (P < 10^− 5), and by decreasing feed particle size (P < 10^− 5). Due to low protein content of the algae extract, the leaching rates of intact and hydrolysed algae extract did not represent absolute estimates for protein and hydrolysed protein leaching. A new estimate for leakage of hydrolysed protein was calculated based on molecular weight distribution of the hydrolysed algae extract analysed by cutoff centrifugation of the extract. Assuming that molecules < 300–600 or < 9–18 kD would leak, leakage of hydrolysed protein from the smallest feed particles after 5 min immersion would be 80–98%, 43–54% and 4–6% of the agglomerated, heat coagulated and protein encapsulated feeds, respectively. The feeds were also tested for preference in cod larvae of two different sizes (5.6 ± 2.5 mg and 15.8 ± 7.2 mg). The preference was highest for the heat coagulated feed in the first experiment (feed intake 0.32 ± 0.06 mg dry feed larvae^− 1) and the agglomerated in the second (2.04 ± 0.32 mg dry feed larvae^− 1), while the protein encapsulated feed was preferred at lower rates in both experiments (0.11–0.14 mg dry feed larvae^− 1).     

Formaldehyde degradation in denitrifying woodchip bioreactors: Effects of temperature,concentration and hydraulic retention time

Formalin is applied in certain aquaculture systems to control parasites infestations as well as bacterial and fungal diseases. This study investigated the capacity of end-of-pipe denitrifying woodchip bioreactors to remove potentially harmful amounts of residual formaldehyde (FA) from aquaculture effluents. Formaldehyde was readily removed by experimental- and field-scale denitrifying woodchip bioreactors and the removal of FA was found to be a combination of an initial adsorption of FA to woodchip surfaces (52 ± 2.8 g FA/m³ woodchips) and microbial degradation. Volumetric FA removal rates reaching 261 ± 27 g FA/m³/d were found at FA inlet concentrations of 90 mg FA/L and hydraulic retention times (HRT) of 5 h. High FA removal efficiencies ranged from 88.3 ± 4.6–99.8 ± 0.2% found for FA inlet concentrations –up to 105 mg FA/L and HRTs between 3.4 and 15 h. Microbial FA degradation rates in woodchip bioreactors were positively correlated to temperature with a Q₁₀ value of 2.27 and a corresponding Arrhenius temperature coefficient of 1.086 for the investigated temperature range of 7–23 °C. At a commercial, outdoor recirculating aquaculture system (RAS) three full-scale woodchip compartments, achieved an average volumetric FA removal rate of 29.4 ± 0.2 g FA/m³/d and a removal efficiency of 82.5 ± 0.8% during the first 24 h following addition of FA. The results demonstrated that woodchip bioreactors are efficient in removing residual FA from RAS effluents and that nitrate removal was transiently enhanced during FA removal.     

Performance of common carp,Cyprinus carpio L. and Nile tilapia,Oreochromis niloticus (L.) in integrated rice–fish culture in Bangladesh

Irrigated rice fields have enormous potential for expanding the aquaculture production in rice producing countries. Two field experiments were carried out at the Bangladesh Agricultural University, Mymensingh, to optimize the productivity of integrated rice–fish systems using Nile tilapia, Oreochromis niloticus (L.), and common carp, Cyprinus carpio L. Both experiments were laid out in a randomized complete block design with three replicates per treatment and regular rice monoculture as control. In the first trial, carp and tilapia were tested in single culture and in mixed culture with supplementary feeding at 2× maintenance level. The highest fish yield was obtained in the carp/tilapia mixed culture (586 ± 125 kg ha^− 1), followed by tilapia alone (540 ± 65 kg ha^− 1), and carp alone (257 ± 95 kg ha^− 1). Carp had significantly lower yield than the other two fish groups (p < 0.05) due to high mortality and inefficient feed utilization. As the carp/tilapia combination performed the best in the first experiment, it was tested with different inputs in the second trial, i.e. regular urea fertilization and two different feeding levels. The feeding levels were: continuous feeding at 2× maintenance level (feed level I) and a declining feeding schedule from 4× to 2× maintenance level (feed level II). The highest fish yield was obtained in feed level II (935 ± 29 kg ha^− 1), followed by feed level I (776 ± 22 kg ha^− 1), and the non-fed group (515 ± 85 kg ha^− 1). Yield differences between the treatments were significant at p < 0.05. Rice yields showed controversial effects between the rice–fish treatments and were dependent on the inputs provided. The highest rice production (4.2 t ha^− 1) was obtained from rice–fish plots with regular urea fertilization. Various significant effects of fish on water quality parameters were observed. Fish decreased the dissolved oxygen (DO) and pH value compared to rice only, especially when supplementary feed was provided. Moreover, fish stimulated the growth of phytoplankton and increased chlorophyll-a concentration. In conclusion, carp/tilapia mixed culture with supplementary feeding was found to be optimal for maximizing the output from rice–fish culture.     

Population dynamics and fishery benefits of a large legal size of a pelagic sportfish,the Talang queenfish,Scomberoides commersonnianus,in northern Australia

The life history of an increasingly important pelagic commercial and sport fish, the Talang queenfish, Scomberoides commersonnianus, was studied in northern Australia to investigate the stock status and assess current management of the species using minimum legal lengths (MLL). Estimated von Bertalanffy growth parameters were L_∞ = 1404 mm FL, K = 0.10 year⁻¹ and t₀ = −1.21 year⁻¹. There was no significant difference in growth between sexes. Ages ranged from 1 to 11 years with age composition differing between the commercial (mainly 6–7 years) and sport fishery (mainly 2–4 years). Females matured (L₅₀) at 635 mm FL and 4–5 years. Spawning occurred between August and March when mature females were estimated to produce 259,488–2,859,935 eggs per spawning. Natural mortality (M) was estimated as 0.16–0.26 year⁻¹, while the combined fishing mortality (F_current) from commercial and sport fisheries was 0.38–0.48 year⁻¹. Yield-per-recruit analyses revealed that under current MLL limits (no MLL or 45 cm TL) and natural mortality (M = 0.16, 0.2 and 0.26 year⁻¹), F_current exceeded the reference points F_max (0.15–0.22 year⁻¹) and F_0.1 (0.10–0.15 year⁻¹), suggesting the stock may be growth overfished if the current situation remains unchanged. Although a stock–recruitment relationship is unknown, spawning stock biomass-per-recruit analysis indicates the stock may also be recruitment overfished since F_current exceeded the reference points F_25% (0.19–0.24 year⁻¹) and F_40% (0.11–0.15 year⁻¹). Increasing the MLL corresponding to L₅₀ of females (70 cm TL) will greatly improve the yield and long-term sustainability of the stock, and also enhance the sport fishery by increasing the number of larger trophy fish.     

Haematological and immunological plasma assays and histological study of the grass carp (Ctenopharyngodon idella) to determine health status

To investigate the health status of farmed Ctenopharyngodon idella, haematology, serum biochemistry, and histology analyses were carried out. Growth performance measurement shows Fulton's condition factor is 1.69. The hepatic somatic index (0.42 ± 0.09) was markedly lower than the reference values (1.2–2.55 ± 0.24). The white blood cell counts (1.57 × 10⁸ ± 0.37 × 10⁷ cell/ml) were approximately 10 times higher than reference values (0.2974 ± 0.00315) × 10⁷ – (1.457 ± 0.69) × 10⁷ cell/ml, as was mean corpuscular volume. The percentage of neutrophil (5.29%) was lower than the reference values (11.59%–39.97%), but thrombocyte proportion (32.32%) was higher than the reference (4.31 ± 7.7%). Activities of plasma alanine transaminase (2.38 ± 1.10 U/L) and aspartate aminotransferase (3.72 ± 1.25 U/L) were lower than reference values (ALT: 4.96–15.84 U/L; AST: 40.66–116.47 U/L). Combined, all reference value of complement C3 content indicates a negative correlation with body size, but C4 and immunoglobulin M was positively correlated. Peroxidase activity was 500 times higher than the reference, possibly due to fish size. Histological diagnosis showed that the Organ indexes (OI) of gill (12.0 ± 8.9) and liver (11.9 ± 12.9) were higher than kidney (7.1 ± 5.5) and intestine (5.0 ± 5.5). Moderate and pronounced histological differences were observed in gills and livers, but the kidney and intestine were mostly normal. This preliminary study has found the difference of health in farmed grass carp and try to reflect the potential health status of farmed fish.     

Metabolic responses of Nephrops norvegicus to progressive hypoxia

This work studied some of the metabolic responses of Nephrops norvegicus to a progressive reduction in water oxygen tension (PwO₂) at 12 °C. Experiments were designed to simulate water quality conditions that may occur during the trade of live crustaceans. Oxygen consumption rates and ammonia efflux rates were found to be constant over a wide range of PwO₂ values (20.4–5.9 kPa). A similar result was found for the difference between post-branchial and pre-branchial oxygen concentrations (20.4–2.6 kPa), obtained from a separate experiment. Anaerobic pathways, however, were activated after PwO₂ reached 6.3 kPa, as blood lactate and glucose concentrations increased from 1.24 ± 0.08 and 1.17 ± 0.19 (T₀ values) to 10.55 ± 8.99 and 3.63 ± 0.89 mg · 100 mL⁻¹ respectively. N. norvegicus was able to maintain blood pH levels at relatively constant values despite a drop in water pH levels and the accumulation of lactate observed at low PwO₂. Heart rates also remained stable during PwO₂ reductions, but scaphognathite beat rate increased considerably, probably as an attempt to maintain steady weight-specific oxygen consumption rates. N. norvegicus appeared to be well adapted to cope with progressive hypoxia as may occur during holding and transportation procedures.