Effectiveness of a strobe light eel exclusion scheme

In the laboratory and field, American eels (Anguilla rostrata) showed a strong avoidance of white strobe light. Eels avoided low light intensities for all strobe flash frequencies tested, and showed no behavioural adaptation to the light source over a prolonged time period. A strobe light barrier was 65–92% effective in repelling upstream migrating eels at Saunders GS on the St. Lawrence River. All size classes of eels were repelled, but effectiveness appeared to be reduced for smaller eels.     

Assessing the use of vibrations and strobe lights at fish screens as enhanced deterrents for two estuarine fishes

The role of vision and the lateral-line system in fish-screen avoidance behaviours was investigated in shiner surfperch Cymatogaster aggregata and staghorn sculpin Leptocottus armatus. Avoidance experiments were conducted in front of water-diversion-type wedge-wire fish screens in a laboratory flume with a 0.3 m s⁻¹ water velocity. Fish contacted the screens less frequently during the day than night, indicating that fish screen avoidance is visually mediated during the day. Input from the fishes' lateral-line systems was also blocked with streptomycin-sulphate treatments during the night to determine if these fishes use mechanoreceptive cues to guide screen avoidance in darkened conditions. Streptomycin-treated and untreated fish had similar contact rates suggesting that mechanoreceptive guidance was not increasing the fishes' abilities to avoid contact with non-vibrating screens at night. Fishes were stained with 2-(4-(dimethylamino)styryl)-N-ethylpyridinium iodide (DASPEI) to assess the streptomycin treatment's effectiveness. We also tested the fishes' ability to avoid contact with the screens at night, when a strobe light or industrial vibrator was operated on the screens, to respectively increase the screen's visual and mechanoreceptory guidance potential. Cymatogaster aggregata contacted the screens significantly less frequently when they were vibrating, compared with their night-time controls, suggesting useful mechanoreceptive guidance. Leptocottus armatus contacted the screens significantly less frequently under strobe-light illumination, compared with their night-time controls, suggesting useful visual guidance. This research should benefit fishery and water-resource managers, regarding the development of future fish-protection decisions at screened water diversions.     

Coloured LED light as a potential behavioural guidance tool for age 0 and 2 year walleye Sander vitreus

Based on existing laboratory research on the visual physiology of walleye Sander vitreus, we tested colours of known spectral sensitivity (i.e., green and orange) using constant and strobing (5 Hz) illumination with an LED-based light guidance device (LGD). Hatchery-reared age 0 and 2 years S. vitreus were exposed to these four light combinations as well as an unilluminated control treatment during day and night trials. Age 2 years S. vitreus generally avoided the LGD when light was produced (negative phototaxis) compared with the control, with continuous illumination having a greater effect than strobing. The proportions of both age 0 and 2 year fish exiting illuminating zones of the trial arena did not differ with light colour or strobe rate, suggesting that phototactic behaviours in S. vitreus do not change with ontogeny in these age classes. Our findings confirm that typical behavioural responses of S. vitreus to light stimuli are characterised by avoidance and provide evidence that the use of light for behavioural guidance (deterrence) may be effective at reducing entrainment and impingement of this species on hydraulic barriers during migrations, independent of ontogenetic stage.     

Reactions in individual fish to strobe light. Field and aquarium experiments performed on whitefish (Coregonus lavaretus)

This study describes how individual whitefish Coregonus lavaretusreact to strobe light. Field experiments were performed in a net enclosure on fish tagged with ultrasonic transmitters. A strobe light array was switched on near the tagged fish. The fish moved away from the light and increased their swimming speed. Aquarium experiments under controlled conditions were carried out in rearing tanks at Saimaa Fisheries and Aquaculture Station in Finland. A strobe light was directed from the side of the basin just ahead of, directly at, and behind the fish at a close range. In the first two cases fish responded by a distinct turn and a change in swimming direction away from the light. The fish did not change its swimming direction when light was aimed from behind. It is concluded that strobe light may be used to prevent fish from swimming into a specific area. Implications for development of new fishing equipment and research concerning fishes in areas with water power stations is briefly discussed.     

Behavioural response of fishes to increasing pH and dissolved oxygen: field and laboratory observations

• 1 Freshwater fish assemblages were sampled quantitatively before, during, and after naturally produced conditions of elevated pH and dissolved oxygen (DO) that occurred for 2–6h in two dense macrophyte beds. Field observations were followed by 3–4-h laboratory behavioural experiments in which banded killifish (Fundulus diaphanus), bluegill (Lepomis macrochirus), and striped bass (Morone saxatilis) were exposed to gradually increasing levels of: (i) pH; (ii) DO; and (iii) pH and DO.
• 2 Field results indicated that the macrophyte bed dominated by Hydrilla verticillata had a higher fish density than the mixed-species (H. verticillata and Vailisneria americana) bed, but beds did not differ significantly in fish species richness or biomass. Within beds, diel changes in fish species composition, richness, density and biomass were minor.
• 3 In the laboratory, avoidance of pH levels exceeding 9.5 was exhibited by all species tested. No significant response was observed to either DO increase treatments, or to pH and DO increase treatments.
• 4 Results suggest fishes do not avoid areas, such as dense macrophyte beds, when high pH levels (9.5–10.0) are accompanied by high DO levels (200–260% saturation).

     

Base and stressed ventilation rates for Leiostomus xanthurus Lacépède and Morone americana (Gmelin) exposed to strobe lights

A biomonitoring system interfaced with a microcomputer was used to monitor ventilation rates for white perch (Morone americana) and spot (Leiostomus xanthurus) under baseline and stressed conditions caused by strobe lights. Tests were conducted on light‐ and dark‐acclimated specimens. These two estuarine species have been found to exhibit avoidance behavior to strobe lights. Potential accommodation to the strobe light stimulus was explored over a 24 h period. The biomonitoring system successfully recorded ventilation rates under baseline and stressed conditions. Baseline mean ventilation rates for 0.5 h intervals ranged from 1 count per minute (cpm) to 97 cpm for light‐acclimated white perch with an overall mean for 24 h (x ) of 41 cpm. Mean stressed rates ranged from 1 to 100 cpm with an overall mean of 44 cpm. Baseline rates for dark‐acclimated white perch ranged from 1 to 79 cpm (x = 35 cpm), with stressed rates from 2 to 83 cpm (x = 30 cpm). Light‐acclimated spot had baseline ventilation rates ranging from 3 to 146 cpm (x = 42 cpm), while stressed rates ranged from 2 to 134 cpm (x = 36 cpm). Mean baseline rates for dark‐acclimated spot ranged from 1 to 94 cpm (x = 40 cpm), and stressed rates ranged from 1 to 72 cpm (x = 25 cpm). The difference in ventilation rates between base and stressed conditions (as absolute values) for light‐acclimated white perch over the 24 h experiments ranged from 0 to 43 cpm (x = 11.01 cpm). Dark‐acclimated white perch had differences ranging from 0 to 78 cpm (x = 11.13 cpm). Light‐acclimated spot had differences ranging from 0 to 101 cpm (x = 14.68 cpm). Dark‐acclimated spot had differences ranging from 0 to 70 cpm (x = 20.56 cpm). Ventilation rates varied between species and among individuals within a species. Ventilation rates were generally lower for dark‐acclimated specimens. For both species under all conditions, the base and stressed rates were significantly (P < 0.05) different during the 24 h period. However, dark‐acclimated specimens exhibited a more distinct difference than light‐acclimated specimens. The lack of accommodation to strobe light and a stronger reaction under dark conditions indicate that strobe lights continue to offer potential as behavioral guidance systems for these species.     

Weight–length relationships for 46 fish species of the Portuguese west coast

Weight–length (W–L) relationships were estimated for 46 species of fish captured off the western Portuguese coast between April 1994 and September 1995. The best‐represented family was Scyliorhinidae (2677 fishes), followed by Gadidae (1871), Sparidae (1682) and Merlucciidae (1108). The estimates for the parameter b of the W–L relationship (W = aL^b) ranged between 2.171 and 3.873, with a median of 3.124. Significant variations in b were found at seasonal level for striped red mullet (Mullus surmuletus), axillary seabream (Pagellus acarne), greater weever (Trachinus draco) and the sardine (Sardina pilchardus), at the regional level for Atlantic mackerel (Scomber scombrus), and between sexes for the small‐spotted dogfish (Scyliorhinus canicula).     

Diel variation in availability and vulnerability of fish to a survey trawl

The effect diel variation in availability and vulnerability has on the fish capture process of a groundfish survey trawl was examined from data collected during an experiment measuring fish escapement underneath the footgear. The survey trawl was significantly more efficient at night in capturing American plaice, Hippoglossoides platessoides, and yellowtail flounder, Limanda ferruginea, but no difference was found in catches of Atlantic cod, Gadus morhua. This increase in capture efficiency at night is related to an increase in availability and vulnerability associated with diel variation in light intensity. No evidence of diel vertical migration was found and changes in availability were linked to visual dependent gear avoidance by the fish. Regardless of light conditions, the survey trawl had a very low capture efficiency for juveniles of the three species studied. Escapement of this size group was extremely high during both day and night periods due to a fast towing speed, use of large bobbin gear, and possible mesh selection.     

A size-dependent migration strategy in Atlantic salmon smolts: Small smolts favour nocturnal migration

Migration theory states that migration behavioural strategies should be optimised to maximise fitness. Many studies have shown that in downstream migrating Atlantic salmon Salmo salar L. smolts, mortality from predation is high and negatively size dependent. The most common predators are birds and piscivorous fish that are mainly daylight feeders. Given the high mortality during this stage we should expect to observe smolts to follow predator avoidance strategies that may be affected by body size. We tested the hypothesis that small smolts have a higher tendency to exhibit predator avoidance strategies (i.e. nocturnal versus diurnal migration) than larger smolts. The number and size of out-migrating/downstream-migrating wild Atlantic salmon smolts was recorded as they passed through a glass-sided channel during April-May, 1996–1999. In all years, the mean size of nocturnal migrating smolts was significantly lower than the mean size of diurnal migrating smolts. Analysis of the size of smolts, during early and late stages of the migration period showed size-dependent nocturnal migration behaviour up to the end of April. After this, no such size dependent migration pattern was observed. However, small smolts (<100 mm) were absent during this period. We suggest that nocturnal migration is an adaptive behaviour that small Atlantic salmon smolts have to avoid predation by large daylight feeding visual piscivorous predators (e.g. pike Esox Lucius L. and fish eating birds).     

Human exposures and potential health hazard assessment of Hg and Pb in some major imported frozen fish species in Nigeria

The levels of mercury and lead in three major species of imported frozen fish—Atlantic mackerel (Scomber scombrus), sardine (Sardinella sindesis), and scumbera (Scumbria spp)—were determined and potential health hazard resulting from their ingestion by Nigerians was assessed. Sample digestion was carried out as prescribed in the Food and Agricultural Organisation/Swedish International Development Agency wet digestion method. Quantitation of the Hg and Pb content of the digested samples and blanks was carried out spectrophotometrically using thiozone as the ligand. The ranges of level of Hg in the samples in mg/Kg were: 0.03–0.42 for Scomber scombrus and 0.03–0.37 and 0.020–0.31 for Scumbria and Sardinella sindesis, respectively. Also, Pb had value ranges in mg/Kg of 0.20–0.28, 0.24–0.32, and 0.15–0.32 in Scomber scombrus, Scumbria, and Sardinella sindesis, respectively. Potential health hazard assessment that was carried out showed no risk status for children and adults consuming Sardinella sindesis and scumbera and adults consuming Scomber scombrus (HQ < 1). The results further showed a risk (HQ = 1.022 and THI = 1.036) for children taking Scomber scombrus.     

School density affects the strength of collective avoidance responses in wild‐caught Atlantic herring Clupea harengus: a simulated predator encounter experiment

An experimental study in a semi‐controlled environment was conducted to examine whether school density in wild‐caught Atlantic herring Clupea harengus affects the strength of their collective escape behaviours. Using acoustics, the anti‐predator diving responses of C. harengus in two schools that differed in density were quantified by exposing them to a simulated threat. Due to logistical restrictions, the first fish was tested in a low‐density school condition (four trials; packing density = 1·5 fish m^?3; c. 6000 fish) followed by fish in a high‐density school condition (five trials; packing density = 16 fish m^?3; c. 60 000 fish). The C. harengus in a high‐density school exhibited stronger collective diving avoidance responses to the simulated predators than fish in the lower‐density school. The findings suggest that the density (and thus the internal organization) of a fish school affects the strength of collective anti‐predatory responses, and the extent to which information about predation risk is transferred through the C. harengus school. Therefore, the results challenge the common notion that information transfer within animal groups may not depend on group size and density.     

Effects of strobe lights on the behaviour of freshwater fishes

When dealing with invasive fishes, permanent barriers may be best in preventing spread; however, they may not be feasible due to various costs and/or logistical constraints. Alternatively, various non-permanent barriers using electricity, light, sound, pressure, bubbles, and CO₂ are being developed and deployed in efforts to limit the spread of aquatic invasive species or to achieve fish guidance and conservation. However, the effectiveness of these barriers is quite variable, and testing is often lacking for both target and non-target species. We conducted a series of laboratory trials to examine the effects of strobe light on behaviour of Common Carp, Brown Bullhead, and Largemouth Bass. In response to strobe lights, Common Carp and Brown Bullhead stayed significantly farther away compared to the control period and resumed their normal activity once the strobe light was turned off. This suggests that strobe lights may prove to be a useful fish deterrent in the field. Our results also highlight the importance of examining the response of both target and non-target species when evaluating fish deterrent technologies.     

Daily rhythms in the somatotropic axis of Senegalese sole (Solea senegalensis): The time of day influences the response to GH administration

Growth factors in vertebrates display daily rhythms, which, while widely described in mammals, are still poorly understood in teleost fish. Here, we investigated the existence of daily rhythms in the somatotropic axis of the flatfish Solea senegalensis. In a first experiment, daily rhythms of the expression of pituitary adenylate cyclase–activating polypeptide (pacap), growth hormone (gh), insulin-like growth factor 1 (igf1) and its receptor (igf1r) were analyzed under a 12:12 h light:dark cycle. All genes displayed daily rhythms with the acrophases of pacap, gh and igf1 located in the second half of the dark phase (ZT 20:28–0:04 h), whereas the acrophase of igf1r was located around mid-light (ZT 5:33 h). In a second experiment, the influence of the time of day (mid-light, ML, versus mid-darkness, MD) of GH administration on the expression of these factors and on plasma glucose levels was tested. The response observed depended on the time of injection: the strongest effects were observed at MD, when GH administration significantly reduced pituitary gh and enhanced liver igf1 expression. These results provide the first evidence of daily rhythms and differential day/night effects in growth factors in S. senegalensis, suggesting new insights for investigating the physiology of growth and possible applications to improve fish aquaculture.     

Age,growth and maturity of tub gurnard (Chelidonichthys lucerna Linnaeus 1758; Triglidae) in the inshore coastal waters of Northwest Wales,UK

The tub gurnard Chelidonichthys lucerna has been identified by ICES as a potential commercial species in the northeast Atlantic with recommendations made to monitor landings and discards and to derive information on population biology for stock assessment purposes, however, data are lacking for the species in the northeast Atlantic. Therefore, aims of this study were to provide data on the size/age‐structure and patterns of growth, maturity and mortality of C. lucerna in Northwest Wales, UK, and in doing so to provide data on the biological characteristics of the most northerly population studied to date for comparison with the existing data for southerly Mediterranean populations. Data on the age, growth and maturity of C. lucerna were collected by otter trawling (73 mm cod‐end stretched mesh size) in the coastal waters of Northwest Wales, UK in October (2000–2011, excluding 2006). Total length (TL) of fish sampled ranged between 10.5–41.0 cm (males) and 10.4–57.5 cm (females). The majority of the female fish were between 20–30 cm TL (60.2%) and the majority of the male fish between 20–30 cm TL (58.3%) respectively. TL/weight (W) relations for male and female fish were similar and the combined data was described by W = 0.0067 TL^3.10. Age of fish ranged between 1–7 years old for female fish and 1–5 years old for male fish respectively with the majority of female fish 3 years old (40%) and the majority of male fish 3 years old (37%). The age structures of female and male tub gurnards were not significantly different with the older age classes consisting predominantly of female fish. Both males and females exhibited similar asymptotic growth patterns and the combined von Bertalanffy growth function was TL_t = 51.6 (1 ? e ^{[?0.25(t + 0.41)]}). Instantaneous rates of total mortality were calculated as 1.04 year^?1 for males and 1.11 year^?1 for females. The size (L₅₀) and age at first maturity (A₅₀) were estimated to be 29.1 cm TL and 2.8 years for males, 27.7 cm TL and 2.7 years for females and 28.0 cm TL and 2.8 years for both sexes combined. The results of this study provide the first information on the biology and population dynamics of C. lucerna in the Irish Sea, the first data collected in the northeast Atlantic since 1985 and the most northerly population studied to date.     

The effect of light stimuli on dark-adapted visual sensitivity in invasive silver carp Hypophthalmichthys molitrix and bighead carp H. nobilis

Non-physical barriers, including the use of underwater strobe lights alone or paired with sound or bubbles, are being considered as a means to prevent the upstream migration of invasive silver carp Hypophthalmichthys molitrix and bighead carp H. nobilis. To optimize potential optical deterrents, it is necessary to understand the visual sensitivity of the fishes. Dark-adapted H. molitrix and H. nobilis were found to possess broad visual sensitivity between 470 to 620 nm with peak spectral sensitivity at 540 nm for H. molitrix and 560 nm in H. nobilis. To assess the effect of a strobe light on vision, dark-adapted H. molitrix, H. nobilis and common carp Cyprinus carpio, were exposed to three different 5 s trains (100, 200, or 500 ms on–off flashes) of white light and the recovery of visual sensitivity was determined by measuring the b-wave amplitude of the electroretinogram (ERG). For all species, the longest recoveries were observed in response to the 500 ms flash trains (H. molitrix mean ± SE = 702.0 ± 89.8 s; H. nobilis 648.0 ± 116.0 s; C. carpio 480 ± 180.0 s). The results suggest that strobe lights can temporarily depress visual sensitivity, which may render optical barriers less effective.     

Selective effect of the duration of the critical temperature period on some allozyme loci of Atlantic salmon Salmo salar L. (Salmonidae)

Genetic structure of juvenile fish from the populations of the Atlantic salmon Salmo salar inhabiting the rivers of Murmansk oblast, Arkhangelsk oblast, and Karelia, as well as of juveniles from hatcheries was examined at five allozymic loci: aspartate aminotransferase (AAT-4*), isocitrate dehydrogenase (IDHP-3*), iditol dehydrogenase (IDDH-2*), esterase D (ESTD*), and malic enzyme (MEP-2*). High genetic differentiation of both natural and “hatchery” juvenile fish was revealed. It was demonstrated that the gene pool of juveniles at three of the five loci tested was to a considerable degree formed by natural selection. In this case, the role of limiting factor was played by the duration of critical temperature regime in the rivers. The differentiation factors for juveniles from nature were not established, however, their clusterization pattern pointed to a possible role of natural selection in this process.     

Screening for Viral Hemorrhagic Septicemia Virus in Marine Fish along the Norwegian Coastal Line

Viral hemorrhagic septicemia virus (VHSV) infects a wide range of marine fish species. To study the occurrence of VHSV in wild marine fish populations in Norwegian coastal waters and fjord systems a total of 1927 fish from 39 different species were sampled through 5 research cruises conducted in 2009 to 2011. In total, VHSV was detected by rRT-PCR in twelve samples originating from Atlantic herring (Clupea harengus), haddock (Melanogrammus aeglefinus), whiting (Merlangius merlangus) and silvery pout (Gadiculus argenteus). All fish tested positive in gills while four herring and one silvery pout also tested positive in internal organs. Successful virus isolation in cell culture was only obtained from one pooled Atlantic herring sample which shows that today''s PCR methodology have a much higher sensitivity than cell culture for detection of VHSV. Sequencing revealed that the positive samples belonged to VHSV genotype Ib and phylogenetic analysis shows that the isolate from Atlantic herring and silvery pout are closely related. All positive fish were sampled in the same area in the northern county of Finnmark. This is the first detection of VHSV in Atlantic herring this far north, and to our knowledge the first detection of VHSV in silvery pout. However, low prevalence of VHSV genotype Ib in Atlantic herring and other wild marine fish are well known in other parts of Europe. Earlier there have been a few reports of disease outbreaks in farmed rainbow trout with VHSV of genotype Ib, and our results show that there is a possibility of transfer of VHSV from wild to farmed fish along the Norwegian coast line. The impact of VHSV on wild fish is not well documented.     

Underwater Video Reveals Strong Avoidance of Chemical Alarm Cues by Prey Fishes

A diversity of fishes release chemical cues upon being attacked by a predator. These cues, commonly termed alarm cues, act as sources of public information warning conspecifics of predation risk. Species which are members of the same prey guild (i.e. syntopic and share predators) often respond to one another's alarm cues. The purpose of this study was to discriminate avoidance responses of fishes to conspecific alarm cues and cues of other prey guild members from responses to unknown damaged fish odours and novel odours. We used underwater video to measure avoidance responses of freshwater littoral species, namely fathead minnows (Pimephales promelas), finescale dace (Chrosomus neogaeus), and brook stickleback (Culaea inconstans), to both injured fish cues and novel non‐fish odours. The cyprinids (minnows and dace) showed significant avoidance of minnow cues over swordtail cues, morpholine, and the control of distilled water and tended to avoid fathead cues over cues of known prey guild members (stickleback). Cyprinids also significantly avoided cues of stickleback over unknown heterospecific cues (swordtail) and tended to avoid stickleback cues over morpholine and the distilled water control. Stickleback significantly avoided fathead minnow extract over the distilled water and tended to avoid stickleback and swordtail over distilled water. We conclude that fishes in their natural environment can show dramatic changes in behaviour upon exposure to alarm cues from conspecifics and prey guild members. These responses do not represent avoidance of cues of any injured fish or any novel odour.     

Unsuitability of Cnesterodon decemmaculatus (Jenyns, 1842) for mosquito control in Uruguay: evidence from food‐preference experiments

We analyzed the feeding preference of Cnesterodon decemmaculatus, a small‐bodied poecilid native from the Rio de la Plata and proximate Atlantic Basins in South America. This species has a wide distribution in Uruguayan water bodies but its effectiveness as a predator of mosquito larvae has not been tested. In laboratory trials, five aquatic invertebrates were offered simultaneously as potential prey to fish: Daphnia pulex (Cladocera), copepods, two different instars of mosquito larvae (Culex pipiens), and the 4^th instar of Chironomidae larvae. Preference was measured by the Chesson's electivity index (α). In order to determine differences in prey preference according to fish size, individuals ranging from 9.5 mm to 35.3 mm were classified in three different body size classes: small, medium, and large. Small fish showed preference for copepods, while medium‐sized fish preferred the smallest mosquito larvae instars and Chironomidae larvae. We conclude that C. decemmaculatus is a zooplankton facultative‐feeder fish that prefers large‐bodied zooplankton but is a weak predator of mosquito larvae. Thus, the introduction of C. decemmaculatus as a biological‐control agent in natural environments is not an effective strategy.