Assessment of efficiency and impacts of gillnets on fish conservation in a tropical freshwater fishery

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Impacts of hydraulic engineering on the dynamics and production potential of floodplain fish populations in Bangladesh

Abstract The present paper examines the impact of hydraulic engineering on fish production potential in Bangladesh by comparing the population dynamics of six species sampled from floodplains inside and outside the Pabna Irrigation and Rural Development Project (PIRDP) during 1995 and 1996. All the sampled populations were dominated by a single cohort for most of the year. Recruitment occurred both inside and outside the flood control scheme, coinciding with floodplain inundation. The growth of all the six species was rapid and strongly seasonal, and all species reached sexual maturity by the end of their first year. With only one exception, growth rates, condition and fecundity were either significantly higher inside the scheme, or not significantly different between the two sampling locations. Differences in growth performance were explained by fish density. No significant differences between sampling locations were detected in the length at maturity (Lm₅₀), spawning period or instantaneous total mortality rate (Z). Estimates of Z were very high for all six species ranging from Z = 3.2 year^?1 to Z = 4.7 year^?1, equivalent to only 4% and 1% survival year^?1, respectively. It was concluded that the production potential of individual fish is at least as high inside as outside the PIRDP and that the 38–51% lower yields per unit area recorded inside the scheme reflect its partial inaccessibility to migrant species.     

Growout production of camouflage grouper, Epinephelus polyphekadion (Bleeker), in a tank culture system

Growout production of the camouflage grouper, Epinephelus polyphekadion (Bleeker), in a 10-m³-capacity fibreglass tank culture system was evaluated, using hatchery-produced fingerlings (56-59 g initial weight) at stocking densities of five, 15 and 45 fish m^?3. During the first 9 months of a 12-month growout period, the fish were fed twice a day with a moist pellet feed containing 40.9% protein. From month 10 onwards until harvest, the fish were fed moist pellets in the morning and trash fish in the evening at a 1:1 ratio. The final weight of fish at harvest was up to 900 g, with mean weights of 544.6 ± 170.72 g at five fish m^?3, 540.2 ± 150.82 g at 15 fish m-^?3 and 513.3 ± 134.52 g at 45 fish m^?3. The results showed no significant differences (P > 0.05) in growth rate and fish size between the different stocking densities tested. The average daily growth rate ranged from 0.62 to 3.38 g fish^?1 day^?1, with mean weights of 1.49 ± 0.74 g fish^?1 day^?1 at five fish m^?3 through 0.53 to 2.38 g fish^?1 day^?1, 1.32 ± 0.57 g fish^?1 day^?1 at 15 fish m^?3 to 0.48-3.32 g fish^?1 day^?1 and 1.31 g fish^?1 day^?1 at 45 fish m^?3 stocking density. Although up to 100% survival was observed at the lowest stocking density, the survival rate significantly decreased (P < 0.05) with increasing stocking density. The food conversion ratio (FCR) significantly decreased (P <0.05) with increasing stocking densities, showing efficient feed utilization with increasing stocking densities of E. polyphekadion. The FCR averaged 2.1 at a stocking density of 45 fish m^?3. The yield in terms of kg fish produced m^?3 of water used in the culture system significantly increased (P < 0.001) from five to 45 fish m^?3. The yield averaged 17.3 ±0.53 kg m^?3 at a stocking density of 45 fish m^?3. The present results show that the present tank culture system could sustain more biomass in terms of increasing fish stocking densities. The growth performance of E. polyphekadion observed during this investigation has been reviewed with other grouper species.     

Effect of Seasonality,Location, and Size on Lipid Content in North Pacific Troll-Caught Albacore Tuna (Thunnus alalunga)

ABSTRACT

Two hundred and thirty-nine albacore tuna (Thunnus alalunga) were troll-caught in the mid-Pacific Ocean and off the US Pacific Coast from June to November 2003. Catch location, harvest date, and sea surface temperature were recorded for individual fish, and lipid and moisture content in the white muscle were determined. The average weight of the alba-core was 6.07 kg and lipid content was highly variable (0.67–18.74%). There was an inverse correlation between the lipid and moisture content of albacore (R² = 0.93), and percent lipid increased slightly in fish caught later on in the season (R² = 0.24). Geographical Information Systems (GIS) software was used to determine correlations between lipid content and geographic location. Lipid content varied considerably among tuna caught at similar latitudes; however, most fish caught below 40°N had a lipid content of less than 10%, while the fish with the highest lipid content (13–19% lipid) were all harvested above 40°N.     

Diversity of siderophore‐producing bacteria isolated from the intestinal tracts of fish along the Japanese coast

This study examined the diversity of siderophore‐producing bacteria in the intestinal tracts of coastal fish in Japan and screened candidate bacterial strains for probiotic use in aquaculture. Of the 2637 bacteria isolated from the 27 fish specimens (13 species) and six environmental samples collected in this study, 266 isolates exhibited the ability to produce siderophores. Siderophore producers were detected in the intestines of 18 of the fish specimens caught (68%) at densities of 2.3 × 10⁴–2.3 × 10⁸ CFU g^?1, in all three seawater samples at 2.0 × 10²–1.3 × 10³ CFU mL^?1 and in all three sand samples at 2.6 × 10¹–2.8 × 10⁴ CFU g^?1. These findings suggest that siderophore‐producing bacteria are widely distributed in the intestinal tracts of coastal fish and their environments. Analysis of 16S rRNA gene sequences revealed that the siderophore producers belonged to 38 species, of which Vibrio splendidus, Vibrio ichthyoenteri and Vibrio crassostreae accounted for 32.7%, 19.5% and 11.3% of the 266 isolates, respectively, suggesting that these bacteria are indigenous to the intestinal tract of coastal fish. Six bacterial species, Enterovibri norvegicus, Photobacterium leiognathi, Photobacterium phosphoreum, Photobacterium rosenbergii, V. crassostrea and Vibrio scophthalmi were identified as possible candidates for use as probionts in fish aquaculture.     

Dynamics of floodplain fisheries in Bangladesh, results of 8 years fisheries monitoring in the Compartmentalization Pilot Project

Floodplain fisheries were monitored from 1992 until 2000 in the Compartmentalization Pilot Project in Tangail, Bangladesh. In permanent floodplains about 165 ± 28 kg ha^?1 of fish was caught annually. For seasonal floodplains, this figure was 83 ± 23 kg ha^?1 yr^?1. The fish catch exhibited a strong seasonal variation, with the highest catch in October, when the floodwater recedes towards the river, and the lowest catch during the dry season in April/May. The annual catch varied with the extent of flooding, with high catches in wet years and low catches in dry years. The extent of flooding was quantified through a Flood Index. Plotting the annual yields against this Flood Index provided a significant relation (P < 0.05), confirming the existence of a flood pulse. The fishing effort (f) and the catch‐per‐unit‐effort (CPUE) were significantly related (P < 0.05), whereby the fishing effort increased with increasing CPUE. The results are discussed within the frame of fisheries management in Bangladesh and highlight the need for long‐term data for proper evaluation of fisheries projects and the development of management schemes, and the difficulty of applying standard surplus production models in floodplain fisheries.     

Effect of stocking density on the growth performance and yield of Nile tilapia [Oreochromis niloticus (L., 1758)] in a cage culture system in Lake Kuriftu,Ethiopia

This research was conducted to investigate the effect of stocking density on the growth performance and yield of Oreochromis niloticus in cage culture in Lake Kuriftu. The treatments had stocking densities of 50 (50F), 100 (100F), 150 (150F), and 200 (200F) fish per m^?3. All treatments were in duplicate. Juveniles with an average weight of 45. 76±0.25 g were stocked in the treatments. The fish were fed a composite mixture of mill sweeping, cotton seed, and Bora food complex at 2% of their body weight twice per day using feeding trays for 150 days in powdered form. The growth performance of O. niloticus was density dependent. The final mean weight of O. niloticus ranged 147.76±0.28–219.71±1.42 g and the mean daily weight gain was 0.69±0.01–1.15±0.02 g day^?1. Fish held in cages with lower density were heavier than the ones held at higher densities, and showed higher weight gain and daily weight gain. The most effective stocking density, in terms of growth parameters, was 50 fish m^?3. The gross yield (4.5–20.55 kg cage^?1) showed a significant difference with increasing stocking density (P<0.05). Moreover, the apparent food conversion ratio (2.48–7.22) was significantly affected by stocking density (P<0.05). However, survival rate was not affected by stocking density (P>0.05). It can be concluded that the most effective stocking densities were at 50 fish m^?3 cage for larger size fish demand in a short period and 200 fish m^?3 for higher gross production with supplementary feed.     

Eastern little tuna,Euthynnus affinis (Cantor, 1849) mature and reproduce within 1 year of rearing in land‐based tanks

Eastern little tuna (ELT, Euthynnus affinis) is expected to see use as a novel aquaculture species due to its rapid growth and high economic value. In this study, closing of the complete life cycle of ELT in land‐based tanks was successfully carried out. Seed production of a first generation (F1) derived from wild‐caught ELT broodstock was conducted in 2010, 2011 and 2012. Survival percentages of F1 ELT at 365 days post hatching for the 2010, 2011 and 2012 year classes were 0.9%, 0.4% and 6.3% respectively. On average, F1 ELT were approximately 40 cm in total length and weighed 1500 g by the time they reached 1 year of age. Successful artificial induction of spawning was achieved in 1‐year‐old F1 ELT using a gonadotropin‐releasing hormone analogue (GnRHa). Induction of spawning was successful at the first administration of GnRHa in the 2010, 2011 and 2012 year classes. First spawning was observed at 4 or 5 days post implantation, which indicated that oogenesis and spermatogenesis progressed within 1 year of rearing in land‐based tanks. During spawning periods, the average number of fertilized eggs and the average number of hatched larvae per spawning event in the 2010, 2011 and 2012 year classes were 20,480 eggs day^?1 and 177 larvae day^?1, 39,423 eggs day^?1 and 9347 larvae day^?1, and 819,555 eggs day^?1 and 674,445 larvae day^?1 respectively. Therefore, it was concluded that both male and female ELT reared in land‐based tanks were capable of reproduction at 1 year of age.     

A multivariate approach to optimization of macronutrient composition in weaning diets for cod (Gadus morhua)

Atlantic cod, initial weight 0.26 g, were fed diets varying in added protein from 530 to 830 g kg^?1, lipid from 50 to 300 g kg^?1 and carbohydrate from 0 to 150 g kg^?1 of dry weight, according to a three‐component mixture design. Analysed values of protein and lipid were 500–770 g kg^?1 and 30–270 g kg^?1, respectively. Analysed carbohydrate levels were as added. Increasing levels of both lipid and carbohydrate had a positive effect on fish growth (P < 10^?3), whereas protein levels above 600 g kg^?1 gave a reduction in growth (P < 10^?4). The effects on growth were evident in fish less than 4 g, whereas fish growth between 4 and 6 g was unaffected by the dietary variation. It is hypothesized that the reduction in growth at high protein levels in fish of less than 4 g could be owing to incomplete utilization of protein, as the stomach of cod is not fully developed before the fish is approximately 1 g. Mortality and cannibalism were high in fish less than 4 g but low when the fish grew from 4 to 6 g. There was a significant decrease in cannibalism with increasing dietary lipid during the first half of the experiment (P < 0.05) and cannibalism was consistently high in fish fed less than 150 g kg^?1 lipid. The lipid level in whole fish increased with increasing dietary levels of lipid (P < 10^?6) and carbohydrate (P < 10^?4), whereas the liver lipid level increased with increasing dietary lipid up to 200 g kg^?1 (P < 10^?6) and decreased thereafter (P < 10^?4). Whole body glycogen increased slightly with increasing levels of dietary carbohydrate (P < 0.05) and was not affected by the other dietary variables. Liver glycogen increased in response to increasing dietary carbohydrate (P < 10^?5) and decreasing levels of dietary lipid (P < 10^?5). An abrupt increase in liver glycogen was seen with the reduction in dietary lipid from 100 to 50 g kg^?1. The hepatosomatic index increased in response to both dietary lipid and carbohydrate (P < 10^?6). It is concluded that the protein requirement of young cod is less than 500 g kg^?1 of dry diet. Fish of less than 4 g should not be given more than 620 g kg^?1 protein and should be supplemented with 150–200 g kg^?1 lipid. Carbohydrate up to 150 g kg^?1 of dry diet promoted growth and did not seem to affect the fish negatively. Fish above 4 g can be given diets varying in protein and carbohydrate over the wide range of concentrations used in the present study, but lipid supplementation should be restricted to between 100 and 200 g kg^?1.     

Evaluation and impact assessment of culture‐based fisheries to enhance fish yield in small reservoirs in Odisha State,India

The present study investigates the success of stocking fingerlings of Indian major carps ‐Gibelion catla (Hamilton), Labeo rohita Hamilton and Cirrhinus mrigala Hamilton – to enhance fish yield in 58 small reservoirs in Odisha State, India. Fish stocking and yield data were collected from State Fisheries Department, Odisha. The relationships between area, stocking density and fish yield of different size groups of reservoirs were assessed using the Pearson correlation coefficient (r). Fish yield increased significantly (p < 0.05, t‐test) from 204 kg/ha/year in 2012–13 to 323 kg/ha/year in 2013–14 due to adoption of CBF. The corresponding per capita fish production increased from 398 kg fisher^?1 year^?1 to 702 kg fisher^?1 year^?1 benefitting more than 8,000 fisher households. Reservoirs in the size group 100–500 ha showed the highest response of fish yield with respect to stocking of fingerlings. The size of fingerlings at stocking and area of the reservoir had greater impact on enhancing fish yield. Stocking had a profound positive impact on fish yield. This study forms a baseline evaluation of the impact of stocking on small tropical reservoirs in India. It also recommends management measures and discusses issues, and the way forward for sustainable fisheries enhancement in small tropical reservoirs in eastern India.     

Analysis of Fishery Records from Cow Green Reservoir, Upper Teesdale, 1971–1980

Apart from some irregularities reflecting changes in permit costs (1975) and the effects of drought (1976), there were increases in angler-visits, catch per angler-visit and number of fish caught during the first 5 years of the fishery. Thereafter, there were about 1000–1500 angler-visits per season, a mean catch of 1.0–1.2 trout per angler-visit and an annual catch of 1200–1800 trout. Between 1971 and 1980 the mean weight of the fish caught fell from 472 to 349 g. During the period 1976–1980 the mean catch per angler-visit was 1.2 fish. This compares favourably with results from a selection of upland and lowland British reservoirs. The mean weight of individual trout caught was 362 kg and this value is typical of both stocked and unstocked upland reservoirs. The mean annual catch during 1976–1980 was about 2 kg ha^?1. This is similar to the values observed in other unstocked upland reservoirs. The gross yield from such reservoirs can be increased by stocking but the limited data available suggest that at stocking rates above about 5 kg ha^?1 the net yield (i.e. weight caught — weight stocked) becomes negative.     

Dietary protein/energy ratios for Atlantic salmon in relation to fish size: growth, feed utilization and slaughter quality

Four extruded diets differing in protein/fat concentrations, 378/389 g kg^?1, 425/346 g kg^?1, 480/308 g kg^?1 and 524/256 g kg^?1 were tested in a digestibility trial and a growth study. Apparent digestibility of protein and fat were not significantly different among the diets when tested in 1-kg Atlantic salmon, Salmo salar L., in sea water. The diets represented a range of digestible protein to digestible energy ratios (DP/DE ratios) of 14.1, 16.4, 18.8 and 21.9 g MJ^?1. The 138-day growth study was performed with triplicate groups of Atlantic salmon of 1.0 and 2.5 kg initial weight. Irrespective of size; growth, feed conversion ratio (FCR), nitrogen and energy retention were poorer in fish fed the diet with DP/DE ratio of 14.1 g MJ^?1 compared with the fish fed the other diets. A DP/DE ratio of 16.4 g MJ^?1 was sufficient to produce maximum growth for the large fish, while the DP/DE ratio of 18.8 g MJ^?1 produced the highest growth in the small fish. In the large fish, the lowest FCR was obtained on a DP/DE ratio of 16.4 g MJ^?1, while there was no clear difference in FCR within the small fish when diets of DP/DE ratios of 16.4–21.9 g MJ^?1 were fed. The carcass-to-body ratio in the small fish decreased with decreasing DP/DE ratios. The fish fed the diet of 21.9 g MJ^?1 had significantly lower fat and dry matter and higher protein content than fish of similar size fed the other diets. Increased dietary lipid content seemed to improve astaxanthin deposition in the small fish, while the large fish showed no significant differences in astaxanthin deposition due to dietary treatment. This study indicates that a DP/DE ratio of 14.1 g MJ^?1 in high-energy diets for Atlantic salmon in sea water is below the optimal DP/DE ratio for growth and feed utilization, and that the optimal DP/DE ratio decreases with increasing fish weight. DP/DE ratios around 19 g MJ^?1 for fish weighing 1 to 2.5 kg, and 16–17 g MJ^?1 for fish weighing 2.5 to 5 kg, are suggested to be optimal.     

Multiresidue determination of antibiotics in aquaculture fish samples by HPLC–MS/MS

An analytical method based on HPLC with MS/MS detection was developed and optimized in order to determine the most useful antibiotics (sulphonamides and tetracyclines) used in aquaculture. A simple extraction procedure, without any clean‐up step, was evaluated in order to obtain maximum analyte recovery from fish samples (Sparus aurata). A mixture of methanol:water 70:30 (v/v)+1 mL EDTA 0.1 M was selected as optimum extractant solution. Because no matrix effects were observed, a standard calibration curve prepared in mobile phase was used for quantification purposes. Antibiotic‐free fish samples were spiked at different concentration levels and analysed by the optimized HPLC method. The average recoveries (n=6) obtained were satisfactory, ranging from 88% to 110% at 100 μg kg^?1. The proposed methodology provided limits of detection for the tested antibiotics in the 1.2–16 μg kg^?1 range, lower than 100 μg kg^?1, the maximum residue level established by the European Union. Finally, commercial fish samples from different origins were analysed in order to confirm the usefulness of the developed methodology.     

Effects of dietary ethoxyquin on growth,feed utilization and residue in the muscle of juvenile Japanese seabass,Lateolabrax japonicus

Ethoxyquin (EQ) is the most common synthetic antioxidant used for preventing rancidity in fish foodstuffs. However, literature related to the effects of dietary EQ on performance of fish was limited. The present study was conducted to investigate the effects of EQ on performance and EQ residue in muscle of juvenile Japanese seabass Lateolabrax japonicus and to estimate the optimal EQ concentration in the diet. Graded levels [0 (control), 50, 150, 450 and 1350 mg EQ kg^?1 diet] of EQ were added to the basal diet, resulting in five dietary treatments in the experiment. Each diet was fed to triplicate groups of seabass (initial body weight 8.01 ± 0.76 g) for 12 weeks in floating sea cages (1.5 × 1.5 × 2.0 m, 30 fish per cage). Survival ranged from 78.9 to 86.7%, and was irrespective of dietary EQ levels. The specific growth rate (SGR) of fish fed diets supplemented with ≤50 mg kg^?1 EQ had significantly (P < 0.05) higher SGR than fish fed diets supplemented with ≥150 mg kg^?1 EQ, the highest SGR was observed in fish fed diet with 50 mg kg^?1 EQ supplementation. Feed intake (FI) and feed efficiency (FE) were not significantly (P > 0.05) different among dietary treatments. Fish fed diets with 50 and 1350 mg kg^?1 EQ had a significant (P < 0.05) lower body lipid content than fish in the control group. Muscle EQ level significantly increased when dietary EQ increased. Optimal EQ concentration estimated by polynomial regression based on maximum growth of juvenile Japanese seabass was 13.78 mg kg^?1 diet.     

Assessment of the aquaculture subsystem in integrated agriculture–aquaculture systems in Northeast Thailand

A survey of integrated agriculture–aquaculture systems (IAAS) was carried out in four different agroecologies, an irrigated and three rainfed agroecologies (drought‐prone, rainfed lowland and rolling land), in Northeast region of Thailand, of tropical wet:dry climate. Fish culture system of IAAS varied with agroecology but not with the length of farmers' experience in IAAS farming. The size of pond holdings in the rainfed lowland agroecology was estimated to be significantly smaller (P≤0.05) than in the three other agroecologies. The highest average extrapolated gross fish yield of 2.3 tonnes ha^?1 was recorded in the irrigated agroecology and this was significantly higher (P≤0.01) than in the three rainfed agroecologies: drought‐prone (1.1 tonnes ha^?1), rainfed lowland (0.5 tonnes ha^?1) and rolling land (0.4 tonnes ha^?1). Higher fish yield in the irrigated agroecology was associated with longer stocking period and higher amount of pond inputs. Average income of IAAS households from fish also varied across agroecology in a fashion that was noted for yields. However, the farm pond played a pivotal role in the diversification of the farming system in rainfed agroecologies, as it was essentially the only source of water supply for fruit and vegetables production. While fish culture in all agroecologies was a low‐input system, intensification through fertilization of ponds with chemical fertilizers can be envisaged to increase fish production in IAAS in Northeast Thailand.     

Rice with fish culture in the semi-deep waters of the Mekong Delta, Vietnam: interaction of rice culture and fish husbandry management on fish production

Fish husbandry and rice culture management factors influencing the yield of introduced fish in ricefields of the Vietnamese Mekong Delta were studied by multiple regression analysis. A significant (P < 0.001) regression model was computed in which feed input and duration of culture period positively and ricefield area, rice seeding rate and the year of the survey negatively affected the yield of introduced, as well as indigenous, fish. The negative impact of larger ricefields is probably the result of the escape of fish. This is also probably the reason for the year of survey since the average yield of introduced fish was 92.5 kg ha^?1 in 1995 (because of an extreme flood) as compared to 164.8 kg ha^?1 in 1994. A high seeding rate of rice results in a dense stand which suppresses the growth of fish. Opportunities for improvement of fish production are proper ricefield construction, reduced seeding rates, stocking fingerlings early in the dry season and more intensive feeding.     

The fate of chlortetracycline residues in a simulated chicken–fish integrated farming systems

Two experiments were conducted at the Asian Institute of Technology, Pathumthani, Thailand to investigate the fate of chlortetracycline (CTC) residue in chicken manure and its effect on integrated chicken–fish farming system. During the first experiment, broiler chickens were raised and CTC residues in their manure were analysed. Chicken fed diets containing 0, 50, 200 and 800 CTC mg kg^?1 had CTC residue levels of 0, 0.9, 3.8 and 6.5 CTC ng g^?1. Once the diet containing CTC was withdrawn, CTC in the manure dropped to negligible amounts (0, 0, 0.2 and 0.5 CTC ng g^?1) within 1 day. Integrated chicken–fish farming systems were simulated during the second experiment to determine the fate of antibiotic residues in chicken manure in aquaculture environment. Chickens were fed a CTC‐free diet and a feed containing CTC at 200 mg kg^?1. Ten 4 m³ square concrete tanks (2 × 2 × 1 m) were used for the experiment. Five tanks were fertilized with CTC‐contaminated manure and the remaining five tanks were fertilized with CTC‐free manure at a rate of 100 kg dry matter ha^?1 day^?1. Sex‐reversed Nile tilapia (Oreochromis niloticus) was stocked at 12 fish tank^?1 on the 14th day after chicken manure application. The immuno‐radio microbial receptor assay (Charm II test) revealed that edible fish muscle, fish intestinal tract and sediment were contaminated by CTC at rates of 7.21, 22.104 and 1.788 ng g^?1, respectively, after 45 days. Chlortetracycline was detected on day 20 in the water column and gradually increased from 0.26 to 12.13 ng g^?1. Chlortetracycline residues were not detected in fish or the aquatic environment of the CTC‐free treatment. The results demonstrate the potential for antibiotic residue accumulation in fish and aquatic environment when CTC‐contaminated chicken manure is used for pond fertilization.     

Replacement of corn with mangrove seeds in bluespot mullet Valamugil seheli diets

Four approximately isoenergetic isonitrogenous diets containing 0, 150, 300 and 510 g kg^?1 mangrove seeds as a replacement for dietary corn in bluespot mullet Valamugil seheli (Valenciennes) commercial feed were fed to triplicate groups (100 fish each) of fingerlings (0.5 g) for 10 weeks. The closed re‐circulating system consisted of 12 cubical tanks (2.25 m³ each). Fish were fed three times a day to satiation. Growth ranked the diets 300 > 150 > 0 > 510 g kg^?1 mangrove seed substitution and in most cases differences in fish weight or SGR were significant (P < 0.05). Proximate composition of fish bodies was affected (P < 0.05) by replacing dietary corn with mangrove seeds in test diets. As the level of mangrove seed incorporation increased, fish body moisture, ash, and protein increased and body fat reduced. Inclusion of mangrove seed up to 300 g kg^?1 as a replacement for corn caused gradual improvement in fish growth performance. Further increase in mangrove seed inclusion (510 g kg^?1) had a negative effect on fish growth performance.     

Studies on the inactivation of selected viral and bacterial fish pathogens at high pH for waste disposal purposes

This study investigated the use of alkaline hydrolysis at ambient temperature for inactivation of selected fish pathogens in fish tissues under conditions approximating those that are likely to be found in the aquaculture industry. Infectious salmon anaemia virus (ISAV) and Lactococcus garvieae have been determined in a previous study to be the most resistant virus and bacteria to pH 12 from a wide range of viruses and bacteria tested. They were spiked at high titres into fish extracts that were then treated with 1 m sodium hydroxide (NaOH). Viable L. garvieae was not detected in the treated fish extract after 1 h, and ISAV was not detected after 24‐h exposure. Field mortalities of Atlantic salmon, Salmo salar L., caused by infectious pancreatic necrosis virus were treated by alkaline hydrolysis at ambient temperature. The macerated fish mortalities contained a high titre of virus (3.38 × 10⁸ TCID₅₀ g^?1) that was reduced to approximately 2.2 × 10³ TCID₅₀ g^?1 after 24‐h exposure to NaOH, and virus was not detected after exposure for 48 h. The results suggest that alkaline hydrolysis at ambient temperature has potential as a biosecure treatment method for fish by‐products containing fish pathogens.     

Estimating post-release survival and the influential factors for recreationally caught Black bream (Acanthopagrus butcheri) in the Glenelg River, south eastern Australia

Black bream (Acanthopagrus butcheri) is the main target species amongst the estuarine recreational fisheries of Victoria, Australia. The A. butcheri fishery is managed through legal-minimum length and daily bag limits. The success of this management strategy requires that the survival rate for released fish is high. This study used the most common angling practices to estimate post-release survival and identify influential factors for undersized A. butcheri in Victoria. In total 1557 and 923 A. butcheri were caught and monitored for initial (≤1 h) and delayed (72 h) survival, respectively. Fish were caught across 3 years, with each year separated into cold and warm water periods with 8 fishing trial days in total. Only 1 of the 266 controls used to assess confinement effects died. Total survival was 95% (S.E. ± 0.8%) for shallow- and 74% (S.E. ± 3%) for deep-hooked fish and decreased as fish length increased. A post-mortem (PM) procedure was developed and showed that throat and gill injuries were the most frequent cause of deep-hooking death. It revealed that 97% of hooks left in fish remained there after 72 h and identified hooking location inaccuracies recorded at the time of capture. Total survival for deep-hooked fish was 20% higher when hooks were left in the fish. Deep-hooked fish were more likely to bleed when hooks were removed and total survival was lower for fish that bleed (58%) than fish that did not bleed (80%). Shallow-hooking rates decreased as fish length increased and were higher during warm water compared to cold water trials. The high shallow-hooking and survival rates observed suggest that A. butcheri survival in the fishery would be high, but deep-hooking has the potential to undermine the management strategy. Determining the shallow-hooking rate in the fishery would help clarify the impact of these findings at the fishery level.