Potential Fish Predators Research Articles

Effects of feeding ration on larval swimming speed and responsiveness to predator attacks: implications for cohort survival

We conducted laboratory experiments to examine the effects of feeding ration on the routine swimming speed of larval striped bass (Morone saxatilis) and their responsiveness to simulated-predator attacks. Striped bass were reared in low (7 prey·L-1), medium (354 prey·L-1), or high (740 prey·L-1) prey treatments from age 4 to 14 days posthatch. Larvae reared in the low-prey treatment had slower routine swimming speeds and shorter reactive distances and were less responsive to simulated-predator attacks. These differences were most pronounced after age 10 and appeared to be an effect of deteriorating larval condition rather than an effect of size. Simulation models were constructed for two potential fish predators, Alosa aestivalis and Pomoxis nigromaculatus, to examine how variation in growth rate, swimming speed, and responsiveness to predator attacks might influence mortality rate. Our simulations predicted that cohort mortality rate would decrease with increasing larval growth rates, even though faster routine swimming speed and growth rate increased encounter rates with predators. The influence of larval growth rate and responsiveness on mortality rate varied between the two predators, but cohorts experiencing no growth always had the greatest mortality rate.

Who dares, learns: chemical inspection behaviour and acquired predator recognition in a characin fish

Individuals that dare approach predators (predator inspection behaviour) may benefit by acquiring information regarding the potential threat of predation. Although information acquisition based on visual cues has been demonstrated for fish, it is unknown whether fish will inspect predators on the basis of chemical cues or whether such inspection behaviour results in information acquisition. Here, we first ascertained whether predator inspection behaviour can be mediated by chemical cues from predators by exposing groups of predator-naive glowlight tetras (Hemigrammus erythrozonus) to the chemical cues of a potential fish predator (convict cichlidCichlasoma nigrofasciatum) that had been fed either tetras (which possess an alarm pheromone) or swordtails (Xiphophorus helleri, which lack Ostariophysan alarm pheromones). Tetras showed a significant increase in antipredator behaviour when exposed to the tetra-diet cue, but not when exposed to the swordtail-diet cue. Chemically mediated predator inspection behaviour was also affected. Both the latency to inspect and the minimum approach distance to the predator significantly increased, and the mean number of inspectors per predator inspection visit significantly decreased when tetras were exposed to the tetra-diet versus the swordtail-diet chemical cues. We then examined a potential benefit associated with chemically mediated predator inspection behaviour. Only tetras that were initially exposed to the tetra-diet cue and that had inspected the predator acquired the visual recognition of a convict cichlid as a predation threat. Our results thus demonstrate that (1) predator inspection behaviour in the glowlight tetra can be initiated by chemical cues, (2) chemically mediated inspection behaviour is affected by the presence of alarm pheromone, and (3) inspectors benefit by acquiring the recognition of novel predators.

Chemical Defenses Against Fish Predation in Three Brazilian Octocorals: 11β,12β-Epoxypukalide as a Feeding Deterrent in Phyllogorgia dilatata

The feeding-deterrence properties of crude extracts of three Brazilian octocoral species, Neospongodes atlantica Kukenthal (Alcyonacea, Nephtheidae), Plexaurella regia Castro (Gorgonacea, Plexauridae), and Phyllogorgia dilatata Esper (Gorgonacea, Gorgoniidae), were investigated. All the extracts were incorporated into food strips at the concentrations occurring in the living organisms. Crude extract and its ethyl acetate fraction obtained from P. dilatata collected in Armacao dos Buzios (Rio de Janeiro State), when incorporated into artificial diets and tested in the habitat of origin, reduced consumption of food strips by fishes, relative to controls. Crude extracts from two octocoral species collected at the National Marine Park of Abrolhos (Bahia State), N. atlantica and P. regia, had no apparent feeding-deterrence properties; in fact, they seemed to stimulate feeding. Bioassay-guided fractionation of the bioactive P. dilatata crude extract revealed that the deterrent property was restricted to a medium polarity fraction. Field palatability experiments with two pure compounds isolated from this fraction revealed that the furanocembranolide 11β,12β-epoxypukalide is a potent feeding deterrent produced by P. dilatata against fish. Apparently, furanocembranolides are a particular class of compounds with feeding deterrent properties, protecting some octocorals from potential fish predator species in both tropical and temperate environments.

Organism response to habitat patchiness: species and habitat-dependent recruitment of decapod crustaceans

Habitat fragmentation from natural or anthropogenic causes is a common phenomenon in shallow water marine habitats such as seagrass beds and oyster reefs throughout the world. Thus, habitat- and scale-dependent information on how organisms perceive and respond to changes in the landscape is critical to efforts aimed at predicting the effects of habitat change on population abundance. In estuarine systems, seagrass is considered one of the predominant nursery habitats for numerous ecologically and commercially important species; however, recent information suggests that alternative habitats such as oyster reefs may also be important sites for settlement and refuge. We used artificial seagrass- and shell-filled plastic trays placed on unstructured seafloor in Back Sound, North Carolina, USA to examine the interactive effects of Experiment, Patch size and Habitat type upon recruitment success of four species of decapod crustaceans: the grass shrimps, Palaemonetes intermedius Holthuis, P. pugio Holthuis and P. vulgaris (Say), and the blue crab, Callinectes sapidus Rathbun. Regardless of habitat type, all species of grass shrimp and J1 blue crab responded to habitat patchiness at scales as small as 0.25 to 4 m −2, whereas larger J2–J4 blue crab did not. Mean densities of all three species of grass shrimp responded in a similar manner to patch size, with significantly higher densities in the smallest patch size (0.25 m −2) compared to larger patches (0.5 to 4 m −2). Conversely, mean densities of J1 blue crabs were significantly higher in the largest patch size (4 m −2) compared to smaller patches (0.25 to 1 m −2). There was a negative and significant relationship between the density of grass shrimp predators and density of J1 prey, and no relationship between potential fish predators and J1–J4 prey. Thus, patterns observed for J1 may be dependent upon predators and not habitat patch size. Both species demonstrated different responses to habitat type depending upon relative densities and body size. Mean densities of P. intermedius and P. vulgaris were higher in seagrass than oyster shell during Experiment 1 (May) when shrimp were relatively abundant, but did not differ between habitat types during Experiment 2 (October), when densities were reduced 10-fold. Conversely, densities of P. pugio did not differ between seagrass and oyster shell. Mean densities of J1 blue crab were similar between seagrass and oyster shell, but higher in seagrass than oyster shell for later juvenile stages (J2–J4). Thus, blue crabs may rely equally on seagrass and oyster reefs as an initial settlement and refuge habitat for early juveniles. Our study demonstrates that an organism's response to habitat patchiness is species-specific, and that for a given species, the response is further modified by animal density and body size. The patterns observed in this study further highlight the importance of scale-dependent responses by mobile organisms to complex benthic habitats.

Predation of juvenile tiger prawns in a tropical Australian estuary

We investigated predation of juvenile penaeids, in particular the grooved tiger prawn Penaeus semisulcatus and the brown tiger prawn P. esculentus, by sampling prawns and their potential fish predators on 2 intertidal seagrass beds in the Embley River, Queensland, Australia. Despite large differences in above-ground biomass of seagrass, these beds are both critical nursery areas for postlarval [ =3 mm CL) tiger prawns. Thirty-seven species of fish were found to eat juvenile penaeids, but 76% of P. semisulcatus and 43% of P. esculentus (numbers) were found in the stomachs of 1 species of fish (Scomberoides commersonianus). Predation levels at the 2 seagrass beds did not appear to be related to the amount of seagrass present; rather the numbers of Penaeus semisulcatus eaten by fish increased with the numbers of P. semisulcatus on the seagrass beds. Compared to the size distributions of tiger prawns resident on the seagrass, postlarval and small juvenile tiger prawns were under-represented in the stomach contents of fish and only 17 of the 287 P. semisulcatus found in fish stomachs were <=4 mm CL. Although we were unable to quantify the component of natural mortality attributable to predation by fish, we have identified the major fish predators of juvenile tiger prawns and provide evidence suggesting that fish are not significant predators of postlarval and small juvenile tiger prawns.

Female mating preference for bold males in the guppy, Poecilia reticulata.

Although females prefer to mate with brightly colored males in numerous species, the benefits accruing to such females are virtually unknown. According to one hypothesis of sexual selection theory, if the expression of costly preferred traits in males (such as conspicuous colors) is proportional to the male's overall quality or reveals his quality, a well-developed trait should indicate good condition and/or viability for example. A female choosing such a male would therefore stand to gain direct or indirect fitness benefits, or both. Among potential phenotypic indicators of an individual's quality are the amount and brightness of its carotenoid-based colors and its boldness, as measured by its willingness to risk approaching predators without being killed. Here, we show experimentally that in the Trinidadian guppy (Poecilia reticulata) the visual conspicuousness of the color pattern of males correlates positively with boldness toward, and with escape distance from, a cichlid fish predator. Bold individuals are thus more informed about nearby predators and more likely to survive encounters with them. Mate-choice experiments showed that females prefer colorful males as mates, but prefer bolder males irrespective of their coloration when given the opportunity to observe their behavior toward a potential fish predator. By preferentially mating with colorful males, female guppies are thus choosing on average, relatively bold, and perhaps more viable, individuals. In doing so, and to the extent that viability is heritable, they potentially gain indirect fitness benefits by producing more viable offspring than otherwise.

Spatial Segregation by Age and Size in Arctic Charr: A Trade-Off between Feeding Possibility and Risk of Predation

1. Arctic charr Salvelinus alpinus underwent phenological and ontogenetic habitat shifts between the epibenthic and pelagic zones in five Norwegian study lakes. Juveniles exploited epibenthic areas until they reached a body length of 13-18 cm when many moved into pelagic waters during summer. 2. Pelagic juvenile Arctic charr had larger age-specific lengths than their epibenthic counterparts, and few juvenile Arctic charr moved from epibenthic to pelagic areas in the presence of large brown trout, the main potential fish predator present

Predator inspection, shoaling and foraging under predation hazard in the Trinidadian guppy,Poecilia reticulata

Guppies,Poecilia reticulata, living in stream pools in Trinidad, West Indies, approached a potential fish predator (a cichlid fish model) in a tentative, saltatory manner, mainly as singletons or in pairs. Such behavior is referred to as predator inspection behavior. Inspectors approached the trunk and tail of the predator model more frequently, more closely and in larger groups than they approached the predator's head, which is presumably the most dangerous area around the predator. However, guppies were not observed in significantly larger shoals in the stream when the predator model was present. In a stream enclosure, guppies inspected the predator model more frequently when it was stationary compared to when it was moving, and made closer inspections to the posterior regions of the predator than to its head. Therefore, the guppies apparently regarded the predator model as a potential threat and modified their behavior accordingly when inspecting it. Guppies exhibited a lower feeding rate in the presence of the predator, suggesting a trade-off between foraging gains and safety against predation. Our results further suggest that predator inspection behavior may account for some of this reduction in foraging. These findings are discussed in the context of the benefits and costs of predator inspection behavior.

Behavioral and trophic plasticity of juvenileTilapia mossambica in utilization of the unstable littoral habitat

JuvenileTilapia mossambica Peters (2.5–10.0 cm standard length) in Lake Sibaya, South Africa, move daily from deep offshore waters to shallow (<0.5 m) littoral areas where they feed for several hours and then return to deep water. The timing of these movements varies in response to changing physical and biological features of the littoral environment. During this study (December 1973 – February 1976), lake level rose more than 1 m. At the start of the study, littoral areas visited by juvenileT. mossambica were free of vegetation and debris, but at higher lake levels trees and brush from the eroding shoreline were common in nearshore littoral waters. When the littoral zone was free of debris, juvenileT. mossambica visited nearshore waters only during daylight hours. After a 0.65 m rise in lake level and considerable accumulation of debris, these fish were abundant in the littoral zone only at night. This reversal can be attributed to efforts by juvenileT. mossambica to avoid their principal predator, the catfishClarias gariepinus. At low lake levelC. gariepinus ventured into the littoral only at night but at higher lake levels this predator was found within flooded vegetation during the day. When further increases in lake level flooded marginal grasslands, juvenileT. mossambica abandoned the littoral zone in favor of this newly created eulittoral habitat where potential fish predators did not occur. With the change in habitat, the diet changed from benthic detrital aggregate to periphyton. These observations suggest the importance of behavioral and throphic plasticity in the ability of tilapia to utilize unstable habitats.

Trends in arthropod defensive secretions, an aquatic predator assay.

Twenty-five arthropod defensive chemicals were tested on a potential fish predator to assay basic repellency, interniche effectiveness and mimetic interactions among repellents, and predator tolerance to repellents.The defensive secretions of aquatic arthropods are more effective repellents than those of terrestrial or cryptozoic arthropods. Phenolic compounds are more effective than carbonylic or acidic compounds. Repellency is most effective in compounds of reduced water solubility. Repeated exposure to gradually increasing molar concentrations of benzoic acid resulted in a greater acceptability of this compound to fish predators. It is suggested that Mullerian mimicry systems based on large numbers of species may be susceptible to dilution effects in terms of effectiveness.