Seeing in the swamp: hydrogen sulfide inhibits eye metabolism and visual acuity in a sulfide-tolerant fish

In fish, vision may be impaired when eye tissue is in direct contact with environmental conditions that limit aerobic ATP production. We hypothesized that the visual acuity of fishes exposed to hydrogen sulfide (H₂S)-rich water would be altered owing to changes in cytochrome c oxidase (COX) activity. Using the H₂S-tolerant mangrove rivulus (Kryptolebias marmoratus), we showed that a 10 min exposure to greater than or equal to 200 µM of H₂S impaired visual acuity and COX activity in the eye. Visual acuity and COX activity were restored in fish allowed to recover in H₂S-free water for up to 1 h. Since K. marmoratus are found in mangrove pools with H₂S concentrations exceeding 1000 µM, visual impairment may impact predator avoidance, navigation and foraging behaviour in the wild.     

Algal Turbidity Reduces Risk Assessment Ability of the Three‐Spined Stickleback

Recent anthropogenic increases in algal turbidity in aquatic habitats have been suggested to affect the ability of fish to assess predation risk. We investigated the response of feeding three‐spined sticklebacks (Gasterosteus aculeatus) exposed to a sudden appearance of an avian predator (the silhouette of common tern, Sterna hirundo), under clear and turbid water conditions. As stickleback use social cues to aid in predator avoidance, we also tested whether turbidity affected social information use by manipulating group size. We found that in turbid water, a smaller proportion of fish would escape from the feeding area, that the distance escaped was shorter and that a smaller proportion of fish fled into shelter. Larger group size was associated with longer escape distance and greater shelter use. However, there was no effect of group size on the proportion of fish that escaped the arena. The effect of group size was similar for turbid and clear water. Our finding that the fish showed a weaker antipredator response suggests that turbidity impedes their risk assessment capability. However, the sticklebacks were still able to benefit of the social facilitation provided by being in a group. This suggests that algal turbidity has detrimental effects on the ability of sticklebacks to assess predation risk from avian predators in shallow water. An implication is that in shallow water fish may be more vulnerable to avian predation under turbid conditions.     

Effects of Turbidity and Visual vs. Chemical Cues on Anti‐Predator Response in the Endangered Fountain Darter (Etheostoma fonticola)

Altered turbidity resulting from anthropogenic stressors is a global problem. Threatened by climate change, pollution, and increased recreational usage, the streams and rivers of central Texas are no exception. The impacts of turbidity include behavioral effects as turbidity degrades visual information, which can impair an animal's ability to accurately detect and respond to a predator. Here, we tested the impact of simulated turbidity on anti‐predator response in the endangered fountain darter, Etheostoma fonticola. We examined the response of E. fonticola to four predator cue treatments (chemical, visual, chemical and visual, and no cues) using a native predator, the green sunfish (Lepomis cyanellus). All cue treatments were tested across two vision levels: clear and impaired, to simulate the visual effects of low turbidity (~30 NTU). Our results indicate that E. fonticola requires a combination of visual and chemical stimuli to respond to a native fish predator. In the absence of one or the other sensory modality, E. fonticola did not show an anti‐predator response. Also, anti‐predator response to a combination of visual and chemical stimuli was only present at the clear vision level. When vision was impaired owing to simulated turbidity, a combination of visual and chemical stimuli did not produce a significant anti‐predator response. These results indicate that blocked or compromised vision hampers anti‐predator response in E. fonticola, which may be of concern regarding the future management of this endangered species.     

Aerial and aquatic visual acuity of the grey bichir Polypterus senegalus,as estimated by optokinetic response

The present study assessed the aerial and aquatic visual abilities of juvenile grey bichir Polypterus senegalus, fish capable of terrestrial locomotion, by measuring the optokinetic response to stimuli of varying speed and spatial frequency. In water, fish tracked slow-moving (2° s⁻¹) stimuli moderately well and fast-moving stimuli very poorly. Spatial acuity was very low compared with many other species, with maximum response observed at 0.05–0.075 stimulus cycles per degree of visual arc; however, it should be noted that adult fish, with their larger eyes, are likely to have somewhat improved spatial acuity. Low spatial acuity and limited stimulus tracking ability might be expected in a nocturnal ambush predator such as P. senegalus, where gaze stabilization may be less crucial and other sensory inputs may have greater importance in perception of the environment. In air, spatial and temporal acuity were both poorer by every measure, but some visual ability persisted. As the eye shows no anatomical specialization for aerial vision, poor vision was expected; however, the large decrease in saccade velocity observed in air trials was unexpected. Stimulus parameters typically have little effect on the characteristics of the saccade, so this finding may suggest that the function of the reflex system itself could be compromised in the aerial vision of some fishes capable of terrestrial locomotion.     

Turbidity amplifies the non‐lethal effects of predation and affects the foraging success of characid fish shoals

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No impact of a presumed manipulative parasite on the responses and susceptibility of fish to simulated predation

Parasites manipulating their host to facilitate trophic transmission is a widespread and diverse phenomenon. Trematode eye‐flukes in the family Diplostomidae infect a variety of fish species as metacercariae, many residing in the eyes. A recently described diplostomid, Tylodelphys darbyi, from the South Island of New Zealand has been found to infect common bully Gobiomorphus cotidianus, an endemic freshwater fish. Within the fish, the metacercariae move about freely in the liquid parts of the eye and are quite large. We hypothesized that increasing intensity of T. darbyi infection will result in increasing visual impairment, thus reducing the ability of G. cotidianus to identify and react to a predatory threat. To test this hypothesis, we performed experiments to (a) examine the fish's reaction to a purely visual predator cue and (b) test their ability to avoid simulated predation under natural levels of infection. Among the 64 fish used in our experiments, T. darbyi had a prevalence of 98.7% with an average of 17.6 worms per fish. However, there was no relationship between T. darbyi intensity and either the fish's reaction to a visual predator stimulus or their ability to escape a simulated predator. Our findings indicate that despite being present in large numbers in the eyes of its fish host, the parasite appears incapable of improving its chances of trophic transmission to its avian definitive host. The results also suggest that the fish G. cotidianus could be using other senses (e.g., olfaction and lateral line) to compensate for visual impairment, and detect and respond to predators.     

Contribution to the feeding ecology of the predatory wingfin anchovy Pterengraulis atherinoides (L.) in north Brazilian mangrove creeks

Stomach contents were examined from 136 Amazonian wingfin anchovy, Pterengraulis atherinoides (Engraulidae), caught from intertidal mangrove creeks at diurnal neap tides between June and September 1997 (early dry season) near Bragança (northern Brazil). The study found that P. atherinoides are specialized predators of juvenile Natantia and Teleostei (mean: 67 and 28% by dry weight, respectively). On average, 5.2 g ha^?1 day^?1 of Natantia and 2.6 g ha^?1 day^?1 of Teleostei (wet weight) were eaten by P. atherinoides. Diet changed with fish size as well as by month. While smaller sizes still fed on several food items (e.g. the copepod Pseudiaptomus marshii, the brachyuran crab Pachygrapsus gracilis, amphipods), fish >13 cm standard length (SL) fed exclusively on Natantia and Teleostei. Copepods were especially abundant in July and August, dominating the diet of fish <9 cm SL in numbers (92%). Our results suggest a positive relationship between predator size and prey size, both in penaeid and piscine prey. However, the largest predator size class apparently selected fewer but larger Teleostei prey. More than 64% of Natantia were juvenile penaeid shrimps of commercial importance (Fenneropenaeus subtilis, F. schmitti, Xiphopenaeus kroyeri). Comparison with ichthyoplankton samples taken simultaneously showed that Sciaenidae and Mugilidae were positively selected while Gobiidae and Engraulidae were negatively selected. The presence of pranzia larvae in the stomachs of fish <10 cm SL, from July onward, suggests that these sizes fulfil a mutually beneficial ‘cleaning’ function on other fish. Block net sampling at neap tides showed that P. atherinoides were present in intertidal mangrove creeks throughout the submergence period, suggesting temporal optimization of the foraging time in the eulittoral.     

Vulnerability of age-0 pallid sturgeon Scaphirhynchus albus to predation; effects of predator type,turbidity, body size,and prey density

Predation can play an important role in the recruitment dynamics of fishes with intensity regulated by behavioral (i.e., prey selectivity) and/or environmental conditions that may be especially important for rare or endangered fishes. We conducted laboratory experiments to quantify prey selection and capture efficiency by three predators employing distinct foraging strategies: pelagic piscivore (walleye Sander vitreus); benthic piscivore (flathead catfish Pylodictis olivaris) and generalist predator (smallmouth bass Micropterus dolomieu) foraging on two size classes of age-0 pallid sturgeon: large (75–100 mm fork length [FL]) and small (40–50 mm FL). Experiments at high (> 70 nephalometric turbidity units [NTU]) and low (< 5 NTU) turbidity for each predator were conducted with high and low densities of pallid sturgeon and contrasting densities of an alternative prey, fathead minnow Pimephales promelas. Predator behaviors (strikes, captures, and consumed prey) were also quantified for each prey type. Walleye and smallmouth bass negatively selected pallid sturgeon (Chesson’s α?=?0.04–0.1) across all treatments, indicating low relative vulnerability to predation. Relative vulnerability to predation by flathead catfish was moderate for small pallid sturgeon (α?=?0.44, neutral selection), but low for large pallid sturgeon (α?=?0.11, negative selection). Turbidity (up to 100 NTU) did not affect pallid sturgeon vulnerability, even at low density of alternative prey. Age-0 pallid sturgeon were easily captured by all predators, but were rarely consumed, suggesting mechanisms other than predator capture efficiency govern sturgeon predation vulnerability.     

Growth of the teleost eye: novel solutions to complex constraints

Synopsis The cichlid fish, Haplochromis burtoni, is highly dependent on vision for survival in its natural habitat. As is true of most teleost fishes, the eyes continue to grow throughout life without any obvious changes in visual capability. In H. burtoni, for example, retinal area may increase by 27 × in just 6 months. During growth, there is no obvious change in the visual sensitivity, visual acuity or lens quality which must all be appropriate for the enlarging eye. This requires that during growth competing constraints be met. For example, to maintain visual acuity, the number of ganglion cells per visual angle subtended on the retina must remain the same as must the convergence ratio of the cones onto those ganglion cells. In contrast, to maintain visual sensitivity, the number of rod photoreceptors per unit retinal area must remain the same. These requirements are in conflict since a larger eye may preserve acuity with fewer cells per unit area in a larger retina. In addition, the lens properties must remain the same as the animal increases in size so that the image available is of similar quality throughout life. Experiments have been performed to reveal the adaptations during growth which allow the fish to preserve its image of the world throughout life.     

Can Paradise Fish (Macropodus opercularis,Anabantidae) Recognize a Natural Predator? An Ethological Analysis

Predator recognition and avoidance by paradise fish have been studied with allopatric species and model experiments. The effect of sympatric predators has not been investigated. Here I report that reactions of paradise fish towards a sympatric predator (Channa micropeltes) are quantitatively different from those shown towards an allopatric predator or different harmless species of fishes. I investigate the possible cues eliciting this differential response and show that visual as well as olfactory stimuli play roles. Olfactory stimuli from the sympatric predator alone elicit an elevated level of activity from paradise fish; the appearance of the sympatric predator (with or without olfactory stimuli) results in an exploratory and display reaction. I speculate what visual stimuli may play roles in predator recognition in paradise fish and I suggest that previously asserted key stimuli such as the eyes of the encountered heterospecific fish may not differentiate the harmful species from innocuous. I conclude that the antipredatory behavior of paradise fish may be affected by both genetic factors and learning and that the relative importance of the former or latter factor may vary depending on the situation.     

Signaling without the risk of illegitimate receivers: do predators respond to the acoustic signals of <Emphasis Type="Italic">Cyprinella</Emphasis> (Cyprinidae)?

Acoustic and visual signals are commonly used by fishes for communication. A significant drawback to both types of signals is that both sounds and visual stimuli are easily detected by illegitimate receivers, such as predators. Although predator attraction to visual stimuli has been well-studied in other animals, predator response to acoustic stimuli has received virtually no research attention among fishes and snakes. This study assessed whether the calls of male tricolor shiner (Cyprinella trichroistia) made during the breeding season would attract potential predators. We also examined the effect of visual stimulus of tricolor shiners on predators. Predators used were red eye bass (Micropterus coosae) and midland water snakes (Nerodia sipedon pleuralis). Neither predator was attracted to tricolor sounds when presented alone. Micropterus coosae responded significantly more to a visual stimulus, and to a combination of visual and acoustic stimuli, but with no greater intensity in the latter. Nerodia sipedon pleuralis did not responded to visual stimulus presented alone, but did respond to visual and acoustic stimuli presented simultaneously, and with greater intensity to the latter, indicating that acoustic signals may play a role in prey detection by N. sipedon pleuralis.     

The evolution of vertebrate eye size across an environmental gradient: phenotype does not predict genotype in a Trinidadian killifish

Vertebrates exhibit substantial variation in eye size. Eye size correlates positively with visual capacity and behaviors that enhance fitness, such as predator avoidance. This foreshadows a connection between predation and eye size evolution. Yet, the conditions that favor evolutionary shifts in eye size, besides the well‐known role for light availability, are unclear. We tested the influence of predation on the evolution of eye size in Trinidadian killifish, Rivulus hartii. Rivulus are located across a series of communities where they coexist with visually oriented piscivores ("high predation" sites), and no predators (“Rivulus‐only” sites). Wild‐caught Rivulus from high predation sites generally exhibited a smaller relative eye size than communities that lack predators. Yet, such differences were inconsistent across rivers. Second‐generation common garden reared fish revealed repeatable decreases in eye size in Rivulus from high predation sites. We performed additional experiments that tested the importance of light and resources on eye size evolution. Sites that differ in light or resource availability did not differ in eye size. Our results argue that differences in predator‐induced mortality underlie genetically‐based shifts in vertebrate eye size. We discuss the drivers of eye size evolution in light of the nonparallel trends between the phenotypic and common garden results.     

The habitats exploited and the species trapped in a Caribbean island trap fishery

We visually observed fish traps in situ to identify the habitats exploited by the U.S. Virgin Islands fishery and to document species composition and abundance in traps by habitat. Fishers set more traps in algal plains than in any other habitat around St. John. Coral reefs, traditionally targeted by fishers, accounted for only 16 % of traps. Traps in algal plain contained the highest number of fishes per trap and the greatest numbers of preferred food species. Traps on coral reefs contained the most species, 41 of the 59 taxa observed in the study. Acanthurus coeruleus was the most abundant species and Acanthuridae the most abundant family observed in traps. Piscivore numbers were low and few serranids were observed. Traps in algal plain contained the most fishes as a result of: ecological changes such as shifts in habitat use, mobility of species and degradation of nearshore habitat (fishery independent); and, catchability of fishes and long-term heavy fishing pressure (fishery dependent). The low number of serranids per trap, dominance of the piscivore guild by a small benthic predator, Epinephelus guttatus, and dominance of trap contents overall by a small, fast-growing species of a lower trophic guild, Acanthurus coeruleus, all point to years of intense fishing pressure.     

Ontogenetic changes in behavioural and histological measures of visual acuity in three species of fish

Synopsis Vision plays an important role in the early life history of fishes. We investigated the ontogenetic changes in visual acuity of early life history stages of alewife,Alosa pseudoharengus, yellow perch,Perca flavescens and bloater,Coregonus hoyi, across a range of sizes. Acuities were determined through histological examination of the retinae of larvae. Reactive distances of larvae to prey were estimated through videophotography of their response to prey and were then converted to measurements of visual angle. Both measures of visual ability improved with size (age) for all species. When behavioural and anatomical measures of ability were compared as a function of size, the data indicate that fish are anatomically more capable of seeing objects than the behavioural response suggests. In two of the three species, the relationship between histological acuity and visual angle was not constant. These results may indicate that while vision may limit initial rates of encounter and feeding, increases in visual acuity mean that in older stages limitations on encounter and feeding are more likely to be behavioural. Furthermore, these results indicate that encounter rates based upon histological estimates of visual acuity will be greater than comparable estimates based upon reactive distances. We recommend calculation of encounter rates based upon reactive distances. Present address: Department of Biology, McGill University, 1205 Ave, Dr. Penfield, Montreal, PQ H3A 1B1, Canada     

Regionalization in the eye of the grapsid crab Neohelice granulata (=Chasmagnathus granulatus): variation of resolution and facet diameters

Crabs have panoramic compound eyes, which can show marked regional specializations of visual acuity. These specializations are thought to be related to the particular features of the animal’s ecological environment. Modern knowledge on the neuroanatomy and neurophysiology of the crabs’ visual system mainly derives from studies performed in the grapsid crab Neohelice granulata (=Chasmagnathus granulatus). However, the organization of the visual sampling elements across the eye surface of this animal had not yet been addressed. We analyzed the sampling resolution across the eye of Neohelice by measuring the pseudopupil displacement with a goniometer. In addition, we measured the facet sizes in the different regions of the eye. We found that Neohelice possesses an acute band of high vertical resolution around the eye equator and an increase in horizontal sampling resolution and lenses diameter towards the lateral side of the eye. Therefore, the analysis of the optical apparatus indicates that this crab possesses greater visual acuity around the equator and at the lateral side of the eye. These specializations are compared with those found in different species of crabs and are discussed in connection to the particular ecological features of Neohelice’s habitat.     

A comparison of Visual Prey Detection Among Species of Piscivorous Salmonids: Effects of Light and Low Turbidities

Differences in reaction distance to prey fish by piscivorous salmonids can alter predator–prey interactions under different visual conditions. We compared reaction distances of three piscivorous salmonids commonly found in western lakes: cutthroat trout, Oncorhynchus clarki utah, rainbow trout, O. mykiss, and the nonnative lake char, Salvelinus namaycush. Reaction distances to salmonid prey were measured as functions of light and turbidity in a controlled laboratory setting. In addition, predation rates and swimming speeds of lake char preying on juvenile cutthroat trout were measured experimentally under a range of light levels. Reaction distances for cutthroat trout and rainbow trout increased rapidly as light levels increased, reaching relatively constant reaction distances at higher light levels. Reaction distances for lake char were similar to cutthroat trout and rainbow trout at the lower light levels; however, lake char reaction distances continued to increase with increasing light intensity to asymptote at distances 65% higher than those for both cutthroat and rainbow trout. Predation rates by lake char were low for the darkest light levels, increased rapidly under low light levels (0.50–0.75lx), and then declined to an intermediate rate at all higher light levels. Swimming speeds by lake char also increased rapidly from extremely low light conditions to a peak and declined to an intermediate level at light levels above 1.00lx. These results suggest that, above the saturation intensity threshold, piscivorous lake char react to fish prey at greater distances than do cutthroat trout and rainbow trout. These differences may help explain the decline of native trout following the introductions of nonnative lake char in lakes and reservoirs of western North America.     

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.     

Altered visual environment affects a tropical freshwater fish assemblage through impacts on predator–prey interactions

1. Increased turbidity and siltation caused by rock quarrying, mining, and deforestation are pervasive disturbances in aquatic systems. Turbidity interferes with vision for aquatic organisms, potentially altering predator–prey interactions.
2. We studied the effects of these disturbances in Trinidadian streams by surveying predators and their shared prey both in streams with versus without quarries as well as in a focal stream before and after the establishment of a quarry. Then, to evaluate whether differential foraging success in turbid water might underlie abundance patterns of predators, we experimentally induced turbidity in mesocosms and measured predator foraging success.
3. Upstream quarry presence had a dramatic effect on the benthic structure of streams, greatly increasing siltation. A substantial decrease in the abundance of a diurnal cichlid predator (Crenicichla frenata) was associated with quarry presence, while a nocturnal erytherinid predator (Hoplias malabaricus) was equally as abundant in streams with or without quarries. The density of their shared prey, the Trinidadian guppy (Poecilia reticulata) remained unchanged.
4. In mesocosm trials, Crenicichla were less successful predators with turbidity, whereas Hoplias performed equally across turbidities. These foraging success results help explain differences in demographic shifts in response to turbidity for both predators.
5. By relating short-term effects of an anthropogenically altered visual environment on species interactions to abundance patterns of predators and prey, this study helps to identify an important mechanism whereby changes to species’ visual ecology may have long-term effects on population biology.

     

Influence of fishes on macroinvertebrate communities and insect emergence production in intermittent stream refuges

1. Drying intermittent stream networks often have permanent water refuges that are important for recolonisation. These habitats may be hotspots for interactions between fishes and invertebrates as they become isolated, but densities and diversity of fishes in these refuges can be highly variable across time and space.
2. Insect emergence from streams provides energy and nutrient subsidies to riparian habitats. The magnitude of such subsidies may be influenced by in-stream predators such as fishes.
3. We examined whether benthic macroinvertebrate communities, emerging adult insects, and algal biomass in permanent grassland stream pools differed among sites with naturally varying densities of fishes. We also manipulated fish densities in a mesocosm experiment to address how fishes might affect colonisation during recovery from hydrologic disturbance.
4. Fish biomass had a negative impact on invertebrate abundance, but not biomass or taxa richness, in natural pools. Total fish biomass was not correlated with total insect emergence in natural pools, but orangethroat darter (Etheostoma spectabile) biomass was inversely correlated with emerging Chironomidae biomass and individual midge body size. The interaction in our models between predatory fish biomass and date suggested that fishes may also delay insect emergence from natural pools, altering the timing of aquatic–terrestrial subsidies.
5. There was an increase over time in algal biomass (chlorophyll-a) in mesocosms, but this did not differ among fish density treatments. Regardless, fish presence in mesocosms reduced the abundance of colonising insects and total invertebrate biomass. Mesocosm invertebrate communities in treatments without fishes were characterised by more Chironomidae, Culicidae, and Corduliidae.
6. Results suggest that fishes influence invertebrates in habitats that represent important refuges during hydrologic disturbance, hot spots for subsidy exports to riparian food webs, and source areas for colonists during recovery from hydrologic disturbance. Fish effects in these systems include decreasing invertebrate abundance, shifting community structure, and altering patterns of invertebrate emergence and colonisation.

     

Balancing algal toxicity and turbidity with predation risk in the three-spined stickleback

Prey may select suboptimal habitat to alleviate predation risk. Algal blooms and turbidity are potentially harmful to prey in aquatic environments, but can provide refugia against predation, given that predators avoid such conditions. Using a flow-through aquarium, we experimentally studied the habitat choice of the three-spined stickleback (Gasterosteus aculeatus L.) provided with toxic and non-toxic bloom-forming cyanobacteria and green flagellate-induced turbidity in the presence and absence of a chemical predator signal from a perch (Perca fluviatilis L.). We investigated whether sticklebacks separate between different algal strains and between turbid and clear water, and whether they are able to use algal toxicity and turbidity as shelter against predators. Sticklebacks preferred the toxic over the non-toxic Nodularia spumigena (Mertens) habitat in the presence of a predator signal, whereas no differences in times spent in the two habitats were detected when the predator signal was absent. There was a tendency for sticklebacks to prefer clear over turbid water in the absence of a predator signal, but no differences were found when the predator signal was present. Our results suggest that the three-spined stickleback is not fully adapted to the cyanobacterial blooms and turbidity caused by the recent eutrophication of the Baltic Sea. However, the predator-induced shifts in habitat choice are also consistent with the hypothesis that sticklebacks use algal toxicity and turbidity as shelters against predation, since these factors are likely to have only minor fitness consequences for sticklebacks.