Effects of angling on post‐release mortality,gonadal development and somatic condition of Australian bass Macquaria novemaculeata

This study assessed the protracted effects of two angling treatments (mild and harsh) on the post‐release mortality, gonadal development and somatic condition of Australian bass Macquaria novemaculeata in a pond‐based experiment. Angled fish were destructively sampled (along with controls) three times: immediately before, and 1 or 4 weeks after release into cages. Compared with the other groups, harshly angled fish had similar, low immediate and short‐term mortalities (≤5%), but significant delayed mortality (25%) and fed only minimally. None of these fish ejected ingested hooks. Forty‐six per cent of captive fish (across all groups) and 20% of wild fish had non‐ripening gonads (stage I) prior to, or during, the experiment. In females with ripening ovaries (stages II or III), neither angling treatment significantly reduced standardized gonadal mass. The mean per cent of atretic oocytes increased among females in all groups, but was significantly greater in those that were harshly angled. The results demonstrated that the gonadal development of M. novemaculeata could be suppressed or impaired (by angling, handling and confinement), and that further research is warranted. In particular, the timing and severity of angling in relation to the stage of gonadal development could have important implications for the introduction of temporal restrictions to angling.     

Mortality of key fish species released by recreational anglers in an Australian estuary

A field experiment was done to quantify the mortality of fish released during a recreational angling tournament in Botany Bay, Australia. Participating boat-based anglers were divided into two groups, each representing different typical catch-and-release events. The first group (termed the ‘live weigh-in group’) retained the largest two individuals of 4 species (dusky flathead, Platycephalus fuscus, yellowfin bream, Acanthopagrus australis, sand whiting, Sillago ciliata, and trevally, Pseudocaranx dentex) in onboard holding tanks and then presented these to researchers at designated weigh-in times and stations. Gear, operational and handling data were collected before 125 fish were tagged using plastic t-bar tags, returned to the anglers and then released into two sea cages. The second group (termed the ‘immediate-release group’) immediately released 224 fish into two sea cages, after they were tagged and relevant data recorded by onboard observers. This group represented those fish routinely discarded (i) as part of catch-and-immediate-release tournaments and/or (ii) due to minimum legal sizes and/or personal quotas. Appropriate species and numbers of ‘control’ fish were seined and placed into two sea cages. All fish were monitored for mortalities over 10 days. Dusky flathead, yellowfin bream, trevally and snapper, Pagrus auratus accounted for more than 85% of the total catch. Their adjusted mortalities ranged between 0% and 36.6%. Irrespective of the treatment, most yellowfin bream and snapper deaths occurred within 3 h of being hooked and released into the cages, while trevally and dusky flathead showed a delayed mortality over 4 days. Owing to confounding effects due to their confinement, dusky flathead were excluded from further analyses. Anatomical hook location and the time between capture and release were significant predictors of mortality for yellowfin bream and trevally, respectively (p < 0.01), but none of the various gear, operational or handling factors examined were significant for snapper (p > 0.05). The results are discussed in terms of species-specific variabilities in mortalities, their causal effects and better management of catch-and-release events.     

Release method and anatomical hook location: effects on short-term mortality of angler-caught Acanthopagrus australis and Argyrosomus japonicus

One field and 3 aquaria experiments were done to quantify the short-term mortality of yellowfin bream Acanthopagrus australis and mulloway Argyrosomus japonicus after being angled and subjected to 3 general handling treatments. Anglers were supplied with identical J-type hooks and asked to handle hooked fish by either (1) physically removing the hook or (2) cutting the line (5 cm from the mouth of the fish) and leaving the hook in. Some hooked A. japonicus were subjected to a third handling treatment where the line was cut underwater without exposing the fish to air. Technical and biological data were collected before all fish were released into sea cages and monitored for 5 d. Control fish were seined and similarly caged and monitored. Concentrations of plasma glucose and cortisol were collected from a sample of fish on the first and last day of the experiments. Significant predictors of mortality for both species involved the presence of blood at the mouth and an interaction between anatomical hook location and hook removal. A. australis and A. japonicus that had their ingested hooks removed experienced the greatest mortalities (87.5 and 72.7%, respectively). Typically, these fish suffered damage to their oesophagus, stomach wall and vital organs. Mortality rates of A. australis and A. japonicus were significantly decreased to 1.7 and 16%, respectively, when they were released with their lines cut, with some of these fish free of hooks after 5 d. In contrast, few mortalities occurred in either species when the hooks were removed or the lines cut on mouth-hooked fish or in A. japonicus when it was released with no air exposure. For A. australis, the field- and aquaria-based experiments provided comparable results in terms of identifying treatment-specific effects, but there were potential biases in rates of hook ingestion. Irrespective of the treatment of fish, all experiments caused physiological changes measured as elevations in either plasma cortisol or glucose. We concluded that anglers should cut the line from hook-ingested A. australis and A. japonicus, but remove the hook from mouth-hooked individuals to prevent subsequent ingestion. Further research is required to examine the longer-term consequences of these handling practices on fish health.     

Ingestion and ejection of hooks: effects on long-term health and mortality of angler-caught yellowfin bream Acanthopagrus australis

Ninety juvenile yellowfin bream Acanthopagrus australis were angled from holding tanks, allowed to ingest nickel-plated, carbon-steel J-hooks and released (with their lines cut) into individual experimental tanks during 2 experiments in order to assess their (1) long-term (up to 105 d) health, mortality and rate of hook ejection and (2) short- and medium-term (< 42 d) temporal changes in health during hook ingestion. Equal numbers of control fish were scooped from holding tanks and similarly monitored in experimental tanks. Of 20 hook-ingested fish released during Expt 1, 3 died within 8 d, providing a non-significant mortality of 15%. Between Day 6 and Day 56 post-release, 13 of the surviving individuals ejected their hooks, which were typically oxidized to about 94% of their original weight and often broken into 2 pieces. At Day 105, there were no significant differences between the 20 control and 17 hook-ingested/-ejected fish in terms of their ability to digest and assimilate food (measured as changes in apparent digestibility coefficients), stress (measured as concentrations of plasma cortisol and glucose) or of morphological parameters that included weight (Wt) and maximum height (MH), maximum width (MW) and maximum girth (MG). During Expt 2, 3 individuals that still contained ingested hooks and 3 controls were sampled on each of 9 occasions between Day 3 and Day 42 post-release. All fish were sampled for blood cortisol and glucose and were then euthanized before being weighed and measured for total length (TL), MH, MW and MG. Hook-ingested individuals were also X-rayed to determine the position and orientation of hooks. There were no significant differences in plasma glucose between hook-ingested and control fish. Irrespective of the treatment of fish, concentrations of cortisol were elevated on some sampling occasions, indicating variable, acute stress. The MH and MG of fish were not significantly different between groups. Significant differences were detected for MG and Wt, with hook-ingested fish having weights similar to those of the control fish but a relatively greater MW (owing to stomach distension from ingested hooks) until 2 wk post-release, after which both morphological parameters generally declined. There was no significant temporal progression of hooks in the stomach of treatment fish; however, some hooks reorientated to positions that may have precluded passage along the digestive tract. We conclude that, for the J-hooks examined, cutting the line is an appropriate strategy that results in the greater majority of released hook-ingested yellowfin bream surviving with minimal negative long-term effects.     

Effects of angling with a single-hook and live bait on muskellunge survival

Use of live bait for angling of muskellunge, Esox masquinongy, is popular in Wisconsin. A traditional method utilizes a large hook through the bait fish’s snout, which requires the muskellunge to swallow the bait prior to hook set. Adult muskellunge (>76 cm; 30 in) were held in lined hatchery ponds and caught while fishing with live bait on 10/0 size single hooks. The leader was cut and the muskellunge was released when hooked in the stomach. Survival was monitored for up to 1 year. No immediate ( <24 h) mortality occurred. However, 22% of hooked muskellunge died within 50 days and 83% died within 1 year. Necropsies revealed extensive trauma to the stomach and other organs from hooks, along with systemic bacterial infections. Highest mortality on both hooked and control fish occurred over winter through spring. This peak mortality may be associated with natural stressors that occur during the spring spawning period. Mortality rates observed in this study are considered unacceptable for trophy management of muskellunge. Although use of live bait for muskellunge is traditional in Wisconsin, terminal tackle such as quick-strike rigs that hook fish in the mouth or buccal cavity should enhance the chances a released muskellunge will survive.     

Mortality and physical damage of angled-and-released dusky flathead Platycephalus fuscus

We completed 2 experiments to quantify the mortality and physical damage (fin, blood and scale loss) of angled dusky flathead Platycephalus fuscus during a live weigh-in tournament (Expt 1) and after being immediately released by anglers (Expt 2). In each experiment, 84 and 79 angled P. fuscus were placed into up to 6 replicate tanks and, along with appropriate numbers of controls, monitored for mortalities over 5 d. Five and 7 of the angled fish died within 12 h, providing mortalities of 3.6 and 8.9% in Expts 1 and 2, respectively. One control fish died, which was attributed to an incorrectly inserted tag. None of the continuous or categorical variables collected during angling and subsequent release, or the experimental design, could explain the few observed mortalities to treatment fish. However, knotted large-mesh landing nets caused significantly greater fin damage than knotless fine-mesh designs in both experiments (p < 0.05). Furthermore, although water quality had no measured impact on the confined fish, the samples taken from anglers' live wells (mostly for Expt 1) were significantly poorer than the environment from which the fish were caught (p < 0.05). These latter differences may have had a cumulative negative impact on fish that manifested as the observed deaths. Simple changes to the post-capture handling of P. fuscus, involving appropriate landing nets and live wells, should reduce some angling impacts on this species.     

Hook performance and selectivity of Eurasian perch,Perca fluviatilis (Linnaeus, 1758) in the Åland Archipelago,Finland

The effects of two hook‐types (circle or J hook) fished with two different baits (red worms Eisenia spp., or cyprinid fishes) were examined for deep‐hooking, catch rate, mean total length, and selectivity of Eurasian perch, Perca fluviatilis, in the Åland Archipelago, Finland. The perch population available to hook‐and‐line gear was sampled with multipanel gillnets, with panels ranging from 10 to 60 mm in stretched mesh diameter. The effect of each hook then was examined for each bait by conditioning the size distributions of hook‐and‐line catches on the size distribution of perch collected with gillnets to estimate selectivity. The proportion of deeply‐hooked perch was 4.8 times greater for J hooks (0.21) than circle hooks (0.04) baited with worms and 3.7 times greater for J hooks (0.33) than circle hooks (0.09) baited with fish. Catch rates were significantly different between the two baits but not between the two hooks, with the greatest catch rate observed for the circle hook baited with worms. There was no significant difference in perch total length between the two hooks, but there was a significant difference between the two baits, with the fish bait catching significantly larger perch. Perch selection peaks between the two hooks differed by only 13.8 mm, but the selection peak with fish bait (236.4 mm TL) was 119.9 mm greater than the selection peak with the worm bait (116.5 mm TL). A substantially lesser incidence of deep hooking support the conservation benefits of circle hook use for perch, especially when catch‐and‐release is practiced. Using fish baits similar in size to those used in this experiment can avoid potentially harmful interactions between relatively small perch and anglers who place little importance on catch motives but whose satisfaction is still catch‐dependent.     

Righty fish are hooked on the right side of their mouths - observations from an angling experiment with largemouth bass, Micropterus salmoides

The development of muscles and bones in fish is laterally asymmetric (laterality). A "lefty" individual has a "C"-shaped body, with its left-side muscles more developed and the left side of its head facing forward. The body of a "righty" is the mirror-image. This laterality causes asymmetric interactions between individuals of different fish species, in that a righty or lefty fish consumes more lefty or righty fish, respectively. To investigate the coupling mechanisms between body asymmetry and predatory behavior, we conducted angling experiments with largemouth bass (Micropterus salmoides). We used the position of the fishhook set in the mouth to indicate the movement direction of the fish when it took the bait. Righty fish had more hooks set on the right side, whereas lefty fish had more on the left side, indicating that righty fish moved more to the left, and lefty fish moved more to the right, in successful catches. The relationship between the hooked position and movement direction was confirmed by video-image analysis of the angling.     

Effects of an experimental short‐term cortisol challenge on the behaviour of wild creek chub Semotilus atromaculatus in mesocosm and stream environments

The consequences of stress on the behaviour of wild creek chub Semotilus atromaculatus outside the reproductive period were studied using a single intra‐coelomic injection of cortisol, suspended in coconut butter, to experimentally raise plasma cortisol levels. Behaviour between cortisol‐treated, sham‐treated (injected with coconut butter) and control S. atromaculatus was compared in a mesocosm system, using a passive integrated transponder array, and in a natural stream system (excluding shams), using surgically implanted radio transmitters. While laboratory time‐course studies revealed that the cortisol injection provided a physiologically relevant challenge, causing prolonged (c. 3 days) elevations of plasma cortisol similar to that achieved with a standardized chasing protocol, no differences in fine‐scale movements were observed between cortisol‐treated, sham‐treated and control S. atromaculatus nor in the large‐scale movements of cortisol‐treated and control S. atromaculatus. Moreover, no differences were observed in diel activity patterns among treatments. Differential mortality, however, occurred starting 10 days after treatment where cortisol‐treated S. atromaculatus exhibited nearly twice as many mortalities as shams and controls. These results suggest that, although the experimental manipulation of cortisol titres was sufficient to cause mortality in some individuals, there were compensatory mechanisms that maintained behaviours (i.e. including activity and movement) prior to death. This study is one of the first to use experimental cortisol implants outside a laboratory environment and during the non‐reproductive period and yields insight into how wild animals respond to additional challenges (in this case elevated cortisol) using ecologically meaningful endpoints.     

Evaluation of pulsed gastric lavage on the survival of captive shovelnose sturgeon

Little is known about the diet of the endangered pallid sturgeon, Scaphirhynchus albus. Because of this endangered status non‐lethal methods to ascertain their food habits must be evaluated. Tests of pulsed gastric lavage (PGL) were conducted on shovelnose sturgeon S. platorynchus, as a surrogate for the pallid sturgeon, to determine if PGL negatively affected their survival. Nine sequential trials containing eight shovelnose sturgeon (N = 72) were conducted with wild fish collected from the Platte River near Louisville, Nebraska. Each trial group was placed into one of two tanks, with each tank containing three pulsed gastric lavaged fish and one control fish. Fish were weighed, measured, and tagged with a passive integrated transponder (PIT tag) before being transported to holding tanks for acclimation and PGL treatment. Sturgeon were acclimated 4–6 days prior to PGL, then held for 15 days after treatment. Temperature, dissolved oxygen, ammonia, and nitrite were monitored daily. No significant difference between the survival of PGL fish and control fish was detected. Because the test required these fish to endure the additional stress of transport and handling, PGL seems a viable technique that can be safely used to evaluate food habits of shovelnose sturgeon, and could be considered safe for pallid sturgeon food habit studies.     

Abundance patterns of the toxic phytoplankton in coastal waters of the Balearic Archipelago (NW Mediterranean Sea): a multivariate approach

The prevalence of catch-and-release factors known to adversely affect the mortality or physical condition of Australian bass Macquaria novemaculeata were surveyed across a range of anglers throughout impoundments and rivers in New South Wales. Subsamples of tournament-caught fish were also monitored in tanks for 1 h after being weighed to quantify immediate mortalities and sublethal physical damage. Most fish were caught on actively fished artificial baits, and were mouth hooked (96%), which resulted in no immediate mortality amongst monitored fish and a low frequency of mortality-causing factors in surveys. However, fish that were weighed-in during tournaments often had fin damage (52% of fish) and/or barotrauma (25% of fish, in impoundments only), and were held in live wells with poor water-quality. The prevalence of these sublethal effects varied considerably according to the specific seasons, locations, rules and procedures of each tournament; but could not be reliably attributed to any of the recorded catch-and-release variables (except for dissolved oxygen, which was significantly influenced by live-well volume). While these results validate the current release of angled Australian bass as a means of conserving their stocks, the potential for adverse effects could nevertheless be minimised via simple changes to conventional handling.     

Chemical excretions of angled bonefish Albula vulpes and their potential use as predation cues by juvenile lemon sharks Negaprion brevirostris

Bonefish Albula vulpes (n = 7) exercised to exhaustion and air exposed for 1 min as part of a catch‐and‐release angling event were found to excrete both ammonia and urea, but cortisol and lactate were below detectable levels. Urea made up a greater proportion of total nitrogen excretion from these fish at all time points following an angling event. When captive juvenile lemon sharks Negaprion brevirostris (n = 12) were exposed to a 30 s pulse of these chemicals [ammonia (500 mM), cortisol (20 µg l^?1), lactate (6 mM) or urea (3 mM)], they showed a significant reduction in the frequency of resting behaviours when exposed to ammonia and urea than when exposed to control water. It appears that products excreted by A. vulpes, particularly ammonia and urea, may provide an olfactory cue for the post‐release predation of A. vulpes by N. brevirostris during catch‐and‐release angling events.     

Lysine and arginine requirements of juvenile Asian sea bass (Lates calcarifer)

Two separate experiments were conducted to determine the dietary requirements of juvenile Asian sea bass Lates calcarifer Bloch for lysine and arginine. Fish (average initial weight: lysine experiment, 13.12 ± 0.12 g; arginine experiment, 2.56 ± 0.13 g) were given amino acid test diets for 12 weeks containing fish meal, zein, squid meal, and crystalline amino acids. Each set of isonitrogenous and isocaloric test diets contained graded levels of L ‐lysine or L ‐arginine. The feeding rate in the lysine experiment was at 4–2.5% of the body weight day^?1, while in the arginine experiment it was at 10–4% of the body weight day^?1. The fish (20 per tank, lysine experiment; 15 per tank, arginine experiment) were reared in 500‐L fibreglass tanks with continuous flowthrough sea water at 27 °C and salinity of 31 ppt in the lysine experiment and at 29 °C and salinity of 29 ppt in the arginine experiment. The experiments were in a completely randomized design with two replicates per treatment. Survival was high in fish given adequate lysine or arginine. Mean percentage weight gains were significantly different in fish fed varying levels of lysine or arginine. Fish fed high levels of L ‐arginine suffered high mortalities. No significant differences were obtained in the feed efficiency ratios (FER, g gain g^?1 feed) of fish fed graded lysine, although the values tended to increase as the dietary lysine level was increased up to the requirement level. In contrast, in the arginine experiment, significant differences in FER of fish among treatments were obtained; the highest FER was observed in fish fed the diet containing an optimum arginine level. On the basis of the growth response, survival, and FER, the lysine and arginine requirements of juvenile Asian sea bass were estimated to be 20.6 g kg^?1 dry diet (4.5% protein) and 18.2 g kg^?1 dry diet (3.8% protein), respectively. These data will be useful in the further refinement of practical diet formulations for the Asian sea bass.     

Long‐term effect of a tidal,hydroelectric propeller turbine on the populations of three anadromous fish species

Tidal hydroelectric power has been proposed as one potential solution for sustainable energy sources. The first tidal turbine in North America began continuous operation in the Annapolis River estuary (44 °45′N; 65° 29′W) in June, 1985. The machine is an axial‐flow, hydraulic‐lift propeller turbine, a type known to cause fish mortality. Anadromous populations of American shad Alosa sapidissima, striped bass Morone saxatilis and Atlantic sturgeon Acipenser oxyrinchus utilize the Annapolis River for spawning and other life history phases. After power generation commenced obvious turbine mortalities of these fishes began appearing downstream of the turbine. Assessments of the A. sapidissima adult spawning runs during 1981–1982 (pre‐operation) and 1989–1996 (operational) indicated significant changes in population characteristics after power generation began. Adult length, mass, age and per cent repeat spawners declined and total instantaneous mortality (Z) increased from 0.30 to 0.55. The pre‐turbine spawning runs had older fish with numerous adult cohorts whereas by 12 years after operation began runs consisted of younger fish with fewer adult cohorts. During 1972–1987 numerous studies indicated the Annapolis River had an important angling fishery for M. saxatilis, but detailed annual records kept by a fishing contest during 1983–1987 and an elite angler family during the period 1976–2008 demonstrated a rapid decline in the number of fish >4.0 kg after turbine operation began. Pre‐turbine catch by the angling family of fish >4.0 kg accounted for 84.1% of total catch, but declined significantly to 39.6% of total catch from 1986–1999, and to none from 2000–2008. The existence of an A. oxyrinchus stock in the Annapolis River was unknown before turbine operation, but during 1985–2017, 21 mortalities were recovered by chance seaward of the turbine. Mechanical strike and cavitation mortalities consisted of juveniles, mature males and gravid and spent females of ages 10 to 53 years found during June to October, the period when this anadromous species returns to its natal river to spawn. The results of the long‐term studies at Annapolis indicate managers should realize substantial risks exist for the fish resources of the world's oceans from deployment of instream propeller turbines.     

Sublethal effects of angling and release on golden perch Macquaria ambigua: implications for reproduction and fish health

The present study tested the hypothesis of no delayed sublethal effects of mild angling and release on the feeding, growth, somatic condition and gonadal development of golden perch Macquaria ambigua during gametogenesis. Subsamples of adult M. ambigua (n = 17–21 of 207), originally captured from the wild and stocked into ten 0·1 ha earthen ponds, were angled and released during early and late gametogenesis. Wild samples that were concurrently collected throughout the experiment underwent rapid and synchronous gonadal development and many spawned. While no spawning occurred in the ponds, most M. ambigua underwent normal gonadal development to maturity, including the angled fish. Angled fish also fed, maintained condition and actually grew faster than non‐angled captive controls. Although females that were angled during late gametogenesis more readily ingested and retained baited hooks, neither their subsequent condition nor gonadal development was significantly affected. The predominance of null results was attributed to the combined effects of the flexible reproductive strategy of M. ambigua, the benignness of mouth hooking and immediate release, and possible methodological issues arising from differential hooking success of more aggressive and resilient individuals. The findings support earlier catch‐and‐release research, but contrast with reports of acute reproductive effects following capture and handling for aquaculture broodstock. This discrepancy highlights the need for research to specifically address welfare questions relevant to recreational fisheries across various species and angling scenarios.     

Salinity‐induced changes to the survival,growth and glycogen distribution in the early fry stages of silver barb,Barbodes gonionotus (Bleeker, 1850)

Five‐week‐old silver barb, Barbodes gonionotus, fry (initial length = 10 mm) were subjected to different salinities of 0, 3, 6 or 9 ppt for 17 days, to then assess their survival and growth. Whole body histological sections were stained with Periodic‐acid Schiff (PAS). Groups of 15 fish were triplicated in each treatment with an ambient temperature (26–28°C). Results showed that growth and condition factor significantly decreased and increased (p < .05), respectively, with the increased salinities after 17 days. While survival was similar (p > .05), between 0 and 6 ppt (at 98% and 87%, respectively), the decrease was significant at 9 ppt (22%). In addition, the fry at 9 ppt had fewer gill mucous cells as well as reduced PAS positive staining intensity within the liver and intestine. This suggests energy was becoming exhausted, leading to mortalities and lower growth. Silver barb early fry were relatively sensitive to elevated salinity, which was likely due to their young age, but short‐term exposure to 3–6 ppt can be used to decrease potential freshwater diseases in the early nursery culture.     

Non‐specific immunity and disease resistance are enhanced by the polysaccharide fraction of a marine chlorophycean macroalga in Oreochromis niloticus (Linnaeus, 1758)

Polysaccharides (PF) from marine macroalgae, Caulerpa scalpelliformis were extracted and tested for its potential immunostimulatory and disease resistance properties in fish. Five groups of Nile tilapia (n = 6), Oreochromis niloticus (Linnaeus, 1758) were intraperitoneally administered with the different doses of PF (2, 20 or 200 mg/kg body weight) or with yeast‐derived commercial immunostimulant, Macrogard^? (20 mg/kg body weight), to compare the effectiveness. An untreated control group was also maintained. A total of fifteen fibre reinforced plastic tanks (150 L, ambient temperature and light conditions) were used, with triplicate tanks for each group. Only four fish per tank (totally 12 fish from a group) were taken at random and assayed. PF enhanced all the tested non‐specific serum immune responses namely lysozyme, myeloperoxidase, antiprotease, and bactericidal activities. There was an upregulation of the genes encoding IL‐1β, lysozyme and TNF‐α in the spleen of PF injected fish as compared to the control group. In order to study the overall functional immunity, disease resistance test was conducted. Another five groups of fish (n = 10) were treated by intraperitoneal injection with different doses of PF or Macrogard^? or untreated as mentioned earlier in triplicates (30 fish per group in three tanks, totally 150 fish in 15 tanks). Seven days post treatment, fish were challenged by intraperitoneal administration of live virulent Aeromonas hydrophila. PF treated fish were protected with significant reduction in the mortality and the consequent increased relative percent survival (RPS) of 92 in the least (2 mg/kg) and middle dose (20 mg/kg) groups. The disease resistance experiment was repeated again but this time, fish were challenged 21 days post treatment that resulted in RPS of 50 for the middle dose. The results clearly show that the intraperitoneal administration of the polysaccharide fraction had a stimulating effect on the non‐specific immune responses, immune gene expression and disease resistance.     

Reducing discard mortality in an estuarine trawl fishery

A purpose-built, water-filled sorting tray was compared against a conventional dry tray for its utility in reducing discard mortality across a range of conditions in an Australian estuarine penaeid-trawl fishery, including the limits of typical delays in starting sorting (2 vs. 15 min). During nine days of fishing, up to 10 replicate deployments were done for each sorting method and delay. Bycatches (44 389 teleosts comprising 15 species) were assessed for their immediate mortalities, before 1346 live individuals (10 species) were released (to simulate discarding) into replicate cages and monitored for their short-term mortalities over five days. Appropriate controls were included for the most abundant economically-important species, yellowfin bream, Acanthopagrus australis. Most trawled-and-discarded teleosts followed a pattern of minimal differences in immediate mortalities between sorting methods for the short delay, but generally fewer deaths in the water tray than in the conventional tray during the longer delay. However, owing to a dominant and slightly protracted influence of the trawling process, comparable rates of deaths were observed for caged fish irrespective of their post-capture treatment. Mixed-effects logistic models applied to four key species (A. australis; silver biddy, Gerres subfasciatus; southern herring, Herklotsichthys castelnaui; and Port Jackson glassfish, Ambassis jacksoniensis) revealed that in addition to the method and delay in sorting, the weights of total catch and jellyfish, salinity and the size of fish also had significant impacts on mortality. For the longer delay in sorting in the water tray, the influences of some of the other factors were negated so that total mortalities of three of the modelled species were reduced by almost one quarter. We conclude that while unaccounted fishing mortality can be reduced via changes to onboard sorting procedures, this approach should only be applied ancillary to efficient gear selectivity.     

Field efficacy and non‐target effects of temephos granules against Culex pipiens (Diptera: Culicidae) and microorganisms in septic tanks,Republic of Korea

A granular formulation of 1.0% temephos (temephos G) was tested for its efficacy in mosquito larval control, residual effects and effects on non‐target microorganisms. Culex pipiens complex in septic tanks in Yangsan, Republic of Korea were used for this study. Microorganisms in the same septic tanks were used for study of non‐target organisms. After the application of temephos G at the rates of 2.0 and 5.0 mg/L to selected septic tanks, mortalities were recorded for 50 days. The effect of temephos G on non‐target organisms was studied by evaluating its effects on the bacterial populations in the treated septic tanks. It was observed that using 1.0% temephos G at a rate of 2.0 mg/L resulted in 100% mortality against Cx. pipiens larvae by the eighth day after treatment. The residual activity of temephos G was observed to continue for a time; for example 29 days after treatment, average larval mortality rates of >68.0% were observed for both concentrations. At the 50th day after treatment, the mortality rates of the Cx. pipiens larvae were observed to decrease to below 42.7% for both concentrations. Application of temephos G did not have significant effects on the bacteria populations in the septic tanks. Since temephos did not seem to have any major effects on the microorganisms, it was concluded that it is a safe and effective larvicide to use in the septic tanks at a rate of 2.0–5.0 mg/L of 1.0% temephos G.     

The effect of environmental colour on the growth,metabolism, physiology and skin pigmentation of the carnivorous freshwater catfish Lophiosilurus alexandri

The growth, physiology and skin pigmentation of pacamã Lophiosilurus alexandri juveniles were evaluated in an experiment using different tank colours (white, yellow, green, blue, brown and black) over an 80 day period. The tank colours did not cause significant differences to final body mass, total length, survival rate, carcass composition (moisture, crude protein, ash, ether extract, calcium, phosphorus, energy), or to plasma protein, triglyceride and cholesterol values. Haematocrit values, however, were highest for fish kept in white tanks (ANOVA P < 0·05), while the greatest haemoglobin levels were recorded for fish kept in blue and brown tanks (P < 0·01). The concentrations of cortisol (P < 0·001) and glucose (P < 0·01) were the most in fish in the black tanks. Tank colour affected skin pigmentation significantly, with fish in white tanks having the highest values of L* (brightness) and the lowest values in blue and black tanks. L*, however, decreased in all treatments throughout the experiment. C*_ab increased significantly over the course of the experiment in fish kept in white tanks. Similar increases of C*_ab were recorded in the other treatments but to a lesser extent. The use of black tanks during the cultivation of L. alexandri caused stress and should be avoided. Cultivation in white and yellow tanks produced individuals with a pale skin colour, while cultivation in blue and black tanks resulted in juveniles with a darker and more pigmented skin.