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.     

Effects of salinity and anatomical hook location on the mortality and physiological response of angled-and-released sand whiting Sillago ciliata

Three experiments were done with sand whiting Sillago ciliata: the first two assessed the short‐term mortality and physiological response of individuals after being mouth hooked and then subjected to rapid changes in salinity, while the third experiment investigated their longer‐term fate after ingesting hooks (independent of salinity changes). In experiment one, 48 tanks containing a single S. ciliata were randomly assigned as either one of three treatments or a control. The fish in treatments one and two were exposed to salinity changes during their angling and subsequent release while those in treatment three were only subjected to angling and air exposure. Control fish remained untouched. Fish were then monitored for up to 6 days for mortalities before blood samples were taken to determine concentrations of plasma cortisol and glucose. Blood samples were also taken from five wild‐caught fish to provide baseline estimates of the above variables. None of the treatment or control fish died over the 6 days, and there were no significant differences in blood cortisol or glucose between treatment, control and wild fish. In experiment two, 102 S. ciliata and 52 experimental tanks were used. The treatments were repeated as above, however, six individuals from each treatment and control group were removed and sampled for blood (and then glucose and cortisol) at 0, 24, 48 and 72 h post release. Some changes in behaviour due to the salinity changes occurred as well as a significant main effect of time for cortisol, with all fish having significantly elevated acute stress at the first sample time. In experiment three, 52 S. ciliata were placed into individual tanks. Twenty‐six of these fish were allowed to ingest baited J‐hooks, played for 60 s, removed from their tanks, and then released after their lines were cut (50 mm from their mouths). Control fish were not touched. All fish were then monitored over 21 days. Six of the treatment fish died (between 3 h and 14 days), while the remaining hooked fish resumed feeding within 5 days and 25% ejected their hooks (between 1 and 19 days). It was concluded that (1) salinity and mouth hooking had few independent or interactive effects on the mortality or physiological response of angled‐and‐released S. ciliata and (2) while hook ingestion caused some mortalities, the protracted physiological effects were limited, with all surviving fish resuming feeding and some eventually ejecting their hooks.     

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.     

Angling-induced cardiac disturbance of free-swimming largemouth bass (Micropterus salmoides) monitored with heart rate telemetry

The sub‐lethal effects of catch‐and‐release angling have been poorly studied because of the difficulties in monitoring physiological parameters in free‐swimming fish. Laboratory studies provide the opportunity to examine sub‐lethal effects in controlled environments, but do not incorporate site‐specific characteristics. In this study we angled free‐swimming largemouth bass (Micropterus salmoides) equipped with heart rate transmitters to exhaustion using rod and reel, and exposed fish to air for 30 s. Experiments were repeated at four water temperatures (13, 17, 21, and 25°C). These field data were compared with published findings from largemouth bass collected at the same water temperatures in a controlled laboratory setting using Doppler flow probes. Field collected heart rate data increased with increasing water temperatures (Q₁₀ values 1.30–1.37). Pre‐disturbance heart rates were ～30% higher for free‐swimming fish in the field than previously collected laboratory data at the same water temperatures. Fish angled in the field exhausted ～40% more rapidly than fish chased in the laboratory. Maximal heart rate was ～15% higher for free‐swimming fish in the field than for data collected from laboratory restrained fish, but scope for heart rate was reduced by up to 20% in the field, especially at higher water temperatures. Heart rate in free‐swimming fish was highly variable at all times, obscuring clear recovery patterns. Conversely, laboratory cardiac parameters exhibited less variable patterns, peaking clearly following disturbances and recovering in about 135 min, independent of water temperature. Based upon these findings, we suggest that comprehensive studies incorporating both laboratory and field experiments are needed for truly understanding the effect of catch‐and‐release angling on fish.     

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.     

Characteristics of Ontario muskellunge (Esox masquinongy) fisheries based on volunteer angler diary information

This paper consolidates and summarizes information on Ontario muskellunge, Esox masquinongy, sport fisheries derived from angler diary programs sponsored by the Ontario Ministry of Natural Resources (OMNR) and Muskies Canada Incorporated (MCI) from 1979 to 2004. Interest in muskellunge as a sport fish has increased substantially over the past 10–15 years. Muskellunge catches were found to be highly correlated with angling effort. Catch rates, expressed in terms of catch-per-unit-of-effort (CUE), have improved over the past decade to the point where, in 2001, the provincial CUE was 0.119. The long term catch rate is 0.069. This improvement in angling quality is attributed to new minimum size limit regulations and increased catch-and-release angling practices. Over the period from 1979–2004, release rates by muskellunge anglers have averaged 94%. Based on a sample size of 9,499 fish, the mean size of angled muskellunge over the past 26 years was 37.0 inches (94 cm). Numerous fish exceeding 50 inches (127 cm) are angled from Ontario waters each year. The incidence of lymphosarcoma, a highly contagious, malignant blood cancer, has averaged only 2% since 1979. Based on an analysis of this information, Ontario’s muskellunge fisheries appear to be stable and sustainable. Volunteer angler diary programs provide an accurate and cost-effective means to monitor the status of muskellunge fisheries in Ontario.     

The effect of catch‐and‐release angling at high water temperatures on behaviour and survival of Atlantic salmon Salmo salar during spawning migration

In this study, behaviour and survival following catch‐and‐release (C&R) angling was investigated in wild Atlantic salmon Salmo salar (n = 75) angled on sport fishing gear in the River Otra in southern Norway at water temperatures of 16·3–21·1° C. Salmo salar were tagged externally with radio transmitters and immediately released back into the river to simulate a realistic C&R situation. The majority of S. salar (91%) survived C&R. Most S. salar that were present in the River Otra during the spawning period 3–4 months later were located at known spawning grounds. Downstream movements (median furthest position: 0·5 km, range: 0·1–11·0 km) during the first 4 days after release were recorded for 72% of S. salar, presumably stress‐induced fallback associated with C&R. Individuals that fell back spent a median of 15 days before commencing their first upstream movement after release, and 34 days before they returned to or were located above their release site. Mortality appeared to be somewhat elevated at the higher end of the temperature range (14% at 18–21° C), although sample sizes were low. In conclusion, C&R at water temperatures up to 18° C had small behavioural consequences and was associated with low mortality (7%). Nevertheless, low levels of mortality occur due to C&R angling and these losses should be accounted for by management authorities in rivers where C&R is practised. Refinement of best practices for C&R may help to reduce mortality, particularly at warmer temperatures.     

Seasonal patterns of winter flounder Pseudopleuronectes americanus abundance and reproductive condition on the New York Bight continental shelf

To resolve varied and sometimes conflicting accounts of spawning and habitat characteristics for winter flounder Pseudopleuronectes americanus, seasonal patterns in abundance and reproductive condition were investigated in the New York Bight, near the southern edge of their current reproductive range. Fish were collected from trawl surveys on the inner continental shelf from October 2006 to October 2007. Pseudopleuronectes americanus were most abundant during January and April surveys, were rarely collected in August, with intermediate abundances in June and October. Measurements of fish condition [hepato‐somatic index (I_H), condition factor (K) and the per cent dry mass of muscle tissue (%M_D)] and reproductive condition [gonado‐somatic index (I_G)] were determined to evaluate seasonal changes in energy accumulation and depletion and reproduction. Males and females had similar patterns in body and reproductive condition, although the magnitude of change was greater for females. I_H values were highest during spring and early summer, suggesting increased feeding following spawning. K and %M_D increased through spring and summer then declined in the autumn and winter concurrent with gonadal development. Gonads began developing in the autumn, and in January, I_G values approached spawning levels, with many spent individuals collected in spring. Within these general patterns, however, there was a large degree of variability among individuals, and a few mature non‐reproductive (‘skipped spawning’) females were observed. In the period after spawning, increased energy intake, indicated by increased I_H, may influence reproductive output since this energy is gradually transferred to the muscle and used for gonadal development in the forthcoming year. The occurrence of ripening individuals on the inner continental shelf in January suggests that these fish either rapidly move into estuaries to spawn by February–March or they remain on the inner shelf to spawn, or some combination of these. Future studies should evaluate these possibilities, as both estuarine and inner shelf habitats are potentially affected by activities such as dredging, sand dredging and wind energy development.     

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.     

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.     

异育银鲫易钓性的表型基础和生态结果及饥饿响应

为考察鲤科鱼类易钓性种内差异的表型基础、生态结果及饥饿响应, 研究以异育银鲫(Carassius auratus gibelio)幼鱼为实验对象, 在饥饿前(对照组)测定其表型特征(能量代谢、游泳能力和个性行为)并垂钓, 随后在饥饿1周后再次垂钓(饥饿组), 最后进行2周的恢复摄食生长实验(恢复组)。垂钓实验具有4个重复, 每个重复的样本量为40尾, 垂钓1.5h即停止, 垂钓20尾为钓出组, 剩余20尾为未钓出组。研究发现: 除钓出组的相对代谢空间(FAS)小于未钓出组外, 钓出组的外部形态(体重、体长和肥满度)、能量代谢参数(标准代谢率SMR、最大代谢率MMR和代谢空间AS)、游泳能力(最大匀加速游泳能力U_cat和最大有氧运动能力U_gt)及个性行为(探索性、活跃性和勇敢性)与未钓出组均无明显差异(所有P>0.05); 在经历捕食者模拟袭击后, 实验鱼勇敢性的潜伏时间比大于探索性, 导致勇敢性的运动时间比和穿门频率小于探索性。SMR与U_cat及U_gt不相关(P>0.05), 但MMR和AS与U_cat及U_gt均呈正相关(P<0.05); 能量代谢参数与个性行为存在部分相关。饥饿增加异育银鲫的垂钓总时间、单尾平均垂钓时间和单尾垂钓时间的变异系数。钓出组在饥饿期的特定生长率(SGR)小于未钓出组, 而恢复期钓出组的SGR与未钓出组无显著差异; 除MMR和AS外, SMR与饥饿期及恢复期的SGR均呈负相关(P<0.05), 即SMR越高个体在饥饿期间的体重下降更快, 在恢复摄食后生长却较慢。研究表明: 异育银鲫幼鱼的易钓性可能不具备表型基础, 并且因环境食物匮乏而降低; 虽然饥饿期间两种易钓性表型个体的生态结果存在差异, 但该生长差异在营养恢复后消失, 表明异育银鲫的易钓性具有一定的环境依赖性。     

Post-release survival and riverine movements of Gulf of Mexico sturgeon (Acipenser oxyrinchus desotoi Acipenseriformes) following induced spawning

Post‐release survival and upstream movement of Gulf of Mexico sturgeon (Acipenser oxyrinchus desotoi) in the Suwannee River, Florida, were examined following induced spawning using carp pituitary extract (CPE). Six mature females (one CPE‐treated and five control) and 12 mature males (five CPE‐treated and seven control) were implanted with ultrasonic tags in March 2001 during their ingress into the Suwannee River. All CPE‐treated sturgeon and 10 of the 12 control fish were relocated using ultrasonic telemetry during 4 months following their release, resulting in 100% survival of treated fish and 83% known survival of control fish. Two control fish (one female and one male) could not be relocated after 2 weeks post‐release. CPE treatment did not result in mortality but did affect upstream movement behavior, with CPE‐treated males moving upstream at a significantly slower rate than control males and females. Similarly, the maximum observed distance that the fish moved upstream differed among control fish (males and females) and treated males, with control fish moving further upstream than CPE‐treated males. The rate of upstream movement for the single CPE‐treated female was similar to the control females and the maximum upstream distance that this female was located was near a putative spawning area. In general, the environmental parameters of temperature, dissolved oxygen, and conductivity differed over the course of the study but did not differ between treatments and sexes. Treating sturgeon with CPE to induce spawning therefore did not cause mortality but did appear to slow the rate of upstream movement and maximum distance moved in male Gulf sturgeon.     

Investigating the Impact of Chronic Atrazine Exposure on Sexual Development in Zebrafish

Atrazine (ATZ) is a selective triazine herbicide used primarily for preemergent weed control in corn, sorghum, and sugar cane production. It is one of the most widely used herbicides in North America. Some research published over the last decade suggests that chronic exposure to environmentally relevant ATZ concentrations can adversely impact gonadal development and/or sexual differentiation in amphibians and fish, while other studies report no effect, or moderate effects. As a result, contrasting conclusions have been published regarding the potential effects of the herbicide ATZ on aquatic species. Two near‐identical 4‐month studies in 2009 (Study I) and 2010 (Study II) were performed investigating the potential for chronic ATZ exposure to affect zebrafish (Danio rerio) sexual development and differentiation. Zebrafish were chronically exposed to 0, 0.1, 1, 10 μM ATZ or 1 nM 17ß‐estradiol (E2). Fish were histologically examined to assign gender and to evaluate potential impacts of E2 or ATZ on gonadal development. Exposure to E2 consistently resulted in a significantly higher proportion of female fish to normal male fish when compared to unexposed fish (both studies). In both studies, ATZ exposure did not significantly influence the percentage of female or male fish when compared to unexposed fish. A greater percentage of abnormally developed male fish and fish lacking differentiated gonadal tissue was observed in Study II E2 exposures but not in ATZ exposures. Together, these studies indicate that long‐term exposure to ATZ at or above environmentally relevant concentrations does not significantly impact zebrafish gonadal development or sexual differentiation.     

Individually assessed boldness predicts Perca fluviatilis behaviour in shoals,but is not associated with the capture order or angling method

Selectivity of recreational angling on fish behaviour was studied by examining whether capture order or lure type (natural v. artificial bait) in ice‐fishing could explain behavioural variation among perch Perca fluviatilis individuals. It was also tested if individually assessed personality predicts fish behaviour in groups, in the presence of natural predators. Perca fluviatilis showed individually repeatable behaviour both in individual and in group tests. Capture order, capture method, condition factor or past growth rate did not explain variation in individual behaviour. Individually determined boldness as well as fish size, however, were positively associated with first entrance to the predator zone (i.e. initial risk taking) in group behaviour tests. Individually determined boldness also explained long‐term activity and total time spent in the vicinity of predators in the group. These findings suggest that individual and laboratory‐based boldness tests predict boldness of P. fluviatilis in also ecologically relevant conditions, i.e. in shoals and in the presence of natural predators. The present results, however, also indicate that the above‐mentioned two angling methods may not be selective for certain behavioural types in comparison to each other.     

Gonad development and size‐at‐maturity of silver therapon Leiopotherapon plumbeus (Kner 1864; Teleostei:Terapontidae) in tropical volcanic lakes in south Luzon,Philippines

Gonad development of the silver therapon Leiopotherapon plumbeus in two volcanic crater  lake  habitats (Sampaloc Lake, Taal Lake) in south Luzon, Philippines was examined during the annual reproductive cycle. The minimum body size‐at‐maturity of fish in these two lake habitats was also compared. Four gonad development stages were characterized as basis for the classification of ovarian (immature, maturing, mature, spawned) and testicular maturation (immature, maturing, mature) phases. The occurrence of all development stages in individual gonads suggest an asynchronous development whereby advanced stages are recruited continuously from a pool of younger stage germ cells to result in elevated female and male GSI throughout the annual cycle due to active gonadogenesis. Together with the increasing occurrence of advanced stage oocytes and spermatozoa from March until October, the elevated GSI of fish may indicate peak gonadal growth during the onset of the dry season (December–January) for eventual spawning from the beginning (May–June) until the end of the wet season (October–November). In both lake habitats, male fish were smaller than females but, regardless of sex, the minimum size‐at‐maturity of fish in Sampaloc Lake was significantly smaller than fish in Taal Lake. Overall, asynchronous development during oogenesis and spermatogenesis allows for year‐round reproduction of silver therapon, with elevated gonad growth in the dry season in preparation for spawning during the wet season. Compared with fish in Taal Lake, a smaller size‐at‐maturity of fish in Sampaloc Lake may be a response of the wild fishery stock to long‐term high fishing mortality and degradation of the lake habitat.     

The effects of early and late androgen treatments on the behavior of Sarotherodon mossambicus (Pisces: Cichlidae)

Groups of Sarotherodon mossambicus were treated with androgen by immersion or oral treatment at various stages of development. Fish were allowed to mature and the effects of treatment on gonadal and behavioral differentiation were examined. The effects of treatment on gonadal differentiation were assessed by determining the sex ratio for each group. Three treatments resulted in sex ratios significantly different from the 1:1 sex ratio obtained in untreated fish. Behavioral differences were detected between groups of males in three measures of territorial defense and aggression, and differences were detected between groups of females in two measures of male-female courtship interaction. A second experiment determined that early-treated females were more sensitive to a second androgen treatment later in life than females not exposed to androgen during development. A number of sex-reversed genetic females functioning as males were detected in two treatment groups with predominantly male sex ratios. There were no differences in the behavior of sex-reversed and non-sex-reversed male fish from the same treatment group. This study establishes that hormone treatments administered during development influence behavioral differentiation in a teleost.     

Angling-Induced Barotrauma in Snapper Chrysophrys auratus: Are There Consequences for Reproduction?

In response to concerns regarding the potential for sub-lethal impacts of barotrauma on reproductively active Chrysophrys auratus during catch and release, 90 males and 90 females representing five reproductive stages (immature or resting-28%, developing-8%, developed-7%, ripe or spawning-23% and spent-34%) were angled from 8–70 m and macroscopically assessed (on-board and then in a laboratory). Irrespective of sex, all fish exhibited various clinical signs of barotrauma, including a prolapsed cloaca (60% of fish); gastric herniation (46%); ruptured swim bladder (73%); organ displacement (48%); and kidney (3%), liver (73%) and coloemic-cavity haemorrhaging (33%);with the frequency of nearly all positively associated with capture depth. Reproductive stage was also an important barotrauma predictor (reflecting related morphological changes) with a general trend towards spent fish least likely to incur the various clinical signs—especially for a prolapsed cloaca (also common among immature or resting fish and significantly affected by food in the digestive tract) and a ruptured swim bladder (common among ripe or spawning fish). The only macroscopically visible gonad damage was haemorrhaging, which was least common among immature or resting and spent fish and, irrespective of reproductive stage, temporally reduced in frequency, and more quickly among males than females. While further research is required to accurately describe the effects of angling at each stage of the reproductive cycle and the physiological consequences of barotrauma on the gonads of C. auratus, given the observed influences of reproductive stage and depth on barotrauma found in this study, any adverse effects might be partially managed by regulating either temporal or spatial fishing effort.     

Ontogeny of sexual development in the roach (Rutilus rutilus) and its interrelationships with growth and age

The roach (Rutilus rutilus) has become a sentinel species for the study of sexual disruption in wild fish populations as a consequence of exposure to endocrine disrupting chemicals (EDCs). Little is known, however, about the normal ontogeny of sexual development in this species. Here, we analyzed the ontogeny of sexual development in captive‐bred roach and assessed how growth rate and fish size affected the timing of both sexual differentiation and sexual development over a 2‐year period. Ovarian differentiation was first recorded at 68 days post‐fertilization (dpf) and this preceded testicular differentiation (first recorded at 98 dpf). In contrast, sexual maturation occurred at an earlier age in males (300 dpf) compared with females (728 dpf). No differences in body size (length or weight) were recorded between male and female roach until the fish were 415 dpf. Studies on three populations of roach which grew at different rates showed that the timing of sexual differentiation was highly variable and more related to fish size than to fish age. Time to sexual maturation was also variable among populations but, subsequent to their first year of life, gonadal status was less well associated with fish size. Interestingly, the sex ratio of the population was biased towards females in populations that grew more rapidly during early life. The findings presented here provide a valuable foundation of work to support both field‐ and laboratory‐based assessments on the effects of EDCs, and other stressors, on sexual differentiation and development in the roach. J. Morphol., 2008. © 2008 Wiley‐Liss, Inc.     

Induction of gonadal maturation at different temperatures in burbot Lota lota

A rearing experiment was conducted to test whether temperature protocols that differed from a simulation of natural conditions might induce maturation after isothermal grow‐out in burbot Lota lota. Lota lota were acclimated to two different temperature regimes: low temperature (LT), close to natural temperature at 4·0° C and elevated, high temperature (HT) at 8·5° C over 40 and 27 days respectively, with all fish then wintered for 47 days. Every second fish was treated with a gonadotropin‐releasing hormone analogue. Maturational competence of oocytes was assessed with a germinal vesicle breakdown assay using a novel staining strategy. In both treatments, puberty and maturational progress occurred, characterised by an elevated gonado‐somatic index and advanced gonadal stages (histological analysis). Progress of gonadal maturation was reflected by elevated plasma concentrations of testosterone and 11‐ketosterone in males and 17β‐oestradiol in females. Ovulation was not observed. Sperm could be activated equally across treatments. In general, LT was more effective than HT treatment, indicated by advanced gonadal stages, higher numbers of oocytes undergoing germinal vesicle breakdown in vitro and elevated sex steroid levels. Hormone treatment could improve effectiveness at HT. In conclusion, less drastic temperature regimes as previously reported in combination with hormone treatments seem sufficient to induce maturation in L. lota after isothermal grow‐out.     

Effects of barotrauma and mitigation methods on released Australian bass Macquaria novemaculeata

The effects of barotrauma on the short-term mortality and physical condition of Australian bass Macquaria novemaculeata were investigated after being: (1) conventionally angled and released during two tournaments in deep impoundments and (2) released untreated or subjected to venting or recompression during a manipulative experiment. All fish were released into two 20 m deep bathy-cages and monitored for 3 days. Of 238 M. novemaculeata angled during the tournaments, 43 (18·1%) had clinical signs of barotrauma or were vented and five of these later died (11·6% mortality). Catch histories varied significantly between both barotrauma and non-barotrauma fish and tournaments, but only hook ingestion significantly influenced mortality (P < 0·05). During the manipulative experiment, venting significantly influenced mortality (13·3%) compared to no treatment or recompression (no deaths). Magnetic resonance images and dissections of barotrauma fish indicated large variation among clinical signs. On the basis of these results, wherever possible M. novemaculeata suffering barotrauma should be immediately released with no treatment. Fish that are unable to resubmerge should be recompressed, while those held in live wells and released in shallow water should be vented.