Behavioural responses of benthic and pelagic Arctic charr to substratum heterogeneity

Responses to environmental heterogeneity were studied in laboratory-reared offspring of two morphs of Arctic charr Salvelinus alpinus from Loch Rannoch, Scotland, one occupying the pelagic zone and feeding predominantly on zooplankton and the other being benthic in habit and feeding mainly on macroinvertebrates. When housed in groups in tanks with a black-and white striped base, benthic charr demonstrated a clear preference for dark areas, whereas pelagic fish positioned themselves at random with respect to substratum colour. In general, pelagic charr were much less aggressive than benthic charr. In pelagic fish, neither spacing nor aggression was affected by the visual heterogeneity of the substrate. In contrast, benthic charr swam closer together and fought more when housed over a uniform as opposed to a non-uniform substratum. The results are discussed in the context of habitat-specific visual requirements and of an interaction between visual complexity and territoriality previously described for Atlantic salmon Salmo salar .     

Behavioural responses of fishes to chemical cues: results from a new bioassay

A new behavioural bioassay for determining the locomotor response by fish to chemical cues is described. The assay combines a behavioural trough, capable of delivering up to 10 discrete plumes of treated water, together with a digital method for quantifying the movements of single fish. Sample responses of two whitefish, Coregonus clupeaformis , one to an attractant (a food extract) and one to a repellant (quinine monohydrochloride), are provided. Their locomotor responses are analyzed in terms of such parameters as total distance travelled, average velocity, number of turns, average excursion distance, and the number of times specific boundaries are crossed. The assay's sensitivity is demonstrated through concentration-response curves by Arctic char, Salvelinus alpinus , to the bile acid, taurocholic acid, and the amino acids, L-serine and L-alanine. Behavioural response threshold concentrations for these three substances were estimated to be 10⁻¹⁵, 10⁻ⁿ, and 10⁻⁹ m, respectively.     

Behavioural variation in juvenile Arctic charr in relation to body size

Young Arctic charr Salvelinus alpinus , derived from one male and one female only from Lake Ölvesvatn in northern Iceland (a stock that has been popular in Icelandic aquaculture), showed large variance in body size, primarily as a consequence of variable egg size. Shortly after the onset of exogenous feeding, large fish (0·11–0·14 g) were more active and fed mainly from the water surface. Small fish (0·06–0·09 g) moved less and made fewer foraging attempts. They spent most of the time on the bottom, and foraged equally on the bottom and surface. These findings can be used to improve growth and performance of juveniles in rearing tanks.     

Behavioural responses of salmonid fry to low amino acid concentrations

The behaviour of start feed brown trout, Salmo trutla , and Atlantic salmon, Salmo salar , fry was observed in response to 5, 50 and 500 nM concentrations of L-alanine, _L-proline, L-arginine and glycine. In addition, salmon fry were tested with dilute concentrations of shrimp extract. Five behaviour patterns (snap, yawn, dart, twitch movements and active swimming) were shown in response to all amino acid and shrimp extract concentrations. Snapping, darting and active swimming increased in both species as a function of amino acid concentration, and in the salmon fry as a function of increasing shrimp extract concentration. Otherwise, the salmon showed twice as much yawning and more twitch movements than the trout, but the trout showed more active swimming than the salmon. Both species showed an increase in activity in response to L-proline at 5 nM, and the salmon also responded to L-arginine and glycine at this concentration. Both species first responded to L-alanine at 50 nM, but the trout did not respond to glycine until a concentration of 500 nM was presented. The salmon fry responded to shrimp extract at c. 10 ¹⁴g l^-1, but no differences in their activity were observed in response to concentrations between c. 10^-12 and 10^-6gl^-1.     

Behavioural responses in a net restraint test predict interrenal reactivity in Arctic charr Salvelinus alpinus

In this study, a 1 min net restraint test was evaluated as a method to predict stress‐coping style in Arctic charr Salvelinus alpinus, by investigating the relationship between behaviour during the test and levels of plasma cortisol sampled after 30 min confinement. In two separate groups of S. alpinus, general linearized model revealed significant correlations between cortisol levels and principal component scores extracted from principal component analysis, combining measures of activity in the tests. With the use of glmulti, the model selection ruled out any effects of size, sex and order of capture on interrenal reactivity. In general, S. alpinus that were more active in the net restraint test also had low levels of circulating cortisol, suggesting a proactive coping style. The results from two repeated runs were not correlated, but both runs, performed eight days apart, show a negative correlation between post‐stress cortisol level and activity in the net. The lack of consistency could be explained by different treatments before each run and individual differences in behavioural plasticity. The net restraint test is thus predictive of stress‐coping style in S. alpinus, and has the benefit of being less time‐consuming than the commonly used confinement stress test.     

Behavioural responses to con- and heterospecific alarm cues by an alien and a coexisting native fish

Hydrobiologia - The monkey goby Neogobius fluviatilis is an invasive Ponto-Caspian fish that enters habitats of the native gudgeon Gobio gobio in European freshwaters, likely belonging to the same...     

Behavioural responses to predator chemical cues and local variation in antipredator performance in Rana temporaria tadpoles

Antipredator behaviour is an important factor influencing survival probability of prey animals, and it may evolve rapidly as a response to changes in predator regime. I studied antipredator behaviour of common frog ( Rana temporaria ) tadpoles from three populations that differ in predator regimes. In the first experiment, tadpoles obtained from four natural matings in each population were subjected to chemical cues from either European perch ( Perca fluviatilis ) or from larvae of the dragonfly Aeshna juncea . Tadpoles decreased their activity in response to both predators, but the spatial behaviour of tadpoles differed between the two predator treatments. In general, there were no differences in behaviours among the populations, but in three out of four studied behaviours there were differences between parentages within the populations suggesting that these behaviours may be genetically determined. The lack of a significant Predator×Population interaction suggests no differences in plastic antipredator behaviour among the populations, while the lack of significant Predator×Parentage interaction suggests no genetic variance within the populations for plastic antipredator behaviour. In the second experiment, tadpoles from the three populations were exposed to predation by a free-ranging A. juncea . In line with the first experiment, there were no differences in survival rate between the populations. R. temporaria tadpoles seem to rely heavily on plastic antipredator behaviour as their main response to predator chemical cues. There was very little indication of local behavioural differentiation and the possible reasons for the lack of divergence among populations are discussed.     

Attraction of slimy sculpins to chemical cues of brook charr eggs

In a laboratory study to examine the responses of slimy sculpin Cottus cognatus to chemical cues of brook charr Salvelinus fontinalis eggs, water that held freshly laid eggs (<20 min old), water-hardened eggs (i.e. eggs >4 h old) or injured eggs was collected and used in a series of two-choice tests. Slimy sculpin were exposed to paired stimuli of (1) hard egg water v . control water, (2) fresh egg water v . control water, (3) hard egg water v . injured egg water or (4) hard egg water v . fresh egg water. Sculpin spent considerably more time on the side of the tank with hard egg water and fresh egg water v . control water and injured egg water v . hard egg water. Sculpin did not show a preference for hard egg water v . fresh egg water. In a field study, brook charr were attracted to chemical cues from brook charr eggs, suggesting that brook charr eggs produce sufficient odour to attract some species under natural conditions.     

Metabolic responses of tadpoles to chemical predation cues

Life-history theory predicts that predator-induced defences should incur fitness costs. In larval amphibians, the most frequently reported cost is reduced energy intake due to lower foraging rates; however, recent reports suggest that this trade-off may be uncoupled through morphological and physiological adaptations. Metabolism is a measure of energy expenditure and plasticity in respiration may potentially offset other costs of predator-induction. The aim of this study was to measure the indirect effects of dragonfly larvae on the respiration rate of tadpoles of the Arabian toad (Bufo arabicus) over time and at different predator concentrations. We performed two experiments. In the first experiment (time–response), we exposed tadpoles either to the indirect presence of odonate larvae or predator-free conditions and measured respiration rates 3, 5, 8, 11, 13, 15, 19 and 26 days after the start of the experiment. In the second experiment (dose–response), we used three levels of predator chemicals, equivalent to 1 predator per 10, 100 or 1,000 l plus controls. The respiration rate of predator-exposed tadpoles varied initially, but was 56.3% of controls after 26 days. In the dose–response experiment, the respiration rate of all predator-exposed tadpole groups was reduced by between 19.1 and 27.2% after 21 days. The study demonstrates a mechanism by which tadpoles may be able to adjust their physiology to partially offset the costs of lower energy intake due to predator avoidance.     

Understanding the toad code: Behavioural responses of cane toad (Chaunus marinus) larvae and metamorphs to chemical cues

Abstract Larvae of many anuran taxa display strong behavioural responses to chemical cues, including alarm signals from injured conspecific tadpoles. We exposed tadpoles and metamorphs from an Australian population of the invasive cane toad (Chaunus[Bufo] marinus) to a range of chemical stimuli and quantified their responses both in the laboratory and in the field. Filtered fluids containing scent cues from crushed conspecifics elicited strong avoidance from tadpoles, whereas other cues (e.g. scent of food, of native‐range fish or urodele predators, and thermal stimuli) did not. Apparent aggregation of tadpoles in response to scent cues proved to be an artifact of tank design, and was an indirect consequence of avoidance of those cues. Field trials confirmed that free‐ranging toad tadpoles and metamorphs avoided chemical cues from crushed conspecifics, suggesting that the chemicals inducing this response might provide an opportunity to develop targeted control methods for this invasive species.     

Behavioural and electrophysiological responses to F-prostaglandins, putative spawning pheromones, in three salmonid fishes

Behavioural and electro-olfactogram (EOG) responses to synthetic F-prostaglandins (PGFs) were recorded in the three salmonids: brown trout Salmo trutta , lake whitefish Coregonus clupeaformis and rainbow trout Oncorhynchus mykiss . Exposure to 10⁻⁸ M PGF_2α and 13, 14-dihydro-PGF_2α increased swimming activity in individually exposed brown trout in a flow-through tank. Digging and nest probing behaviours were further observed in brown trout females exposed to PGF_2α. Lake whitefish exposed to 10⁻⁸ M PGF_2α and 15-keto-PGF_2α also increased their locomotion. In rainbow trout, the absence of behavioural responses to PGFs correlates with a lack of olfactory sensitivity to these chemicals. PGFs triggered behavioural responses distinct from the feeding stimulant in brown trout. EOG measurements demonstrated that brown trout were most sensitive to PGF_2α, with a threshold concentration of 10⁻¹¹ M. Lake whitefish were most sensitive to both 15-keto-PGF_2α and 13, 14-dihydro-PGF_2α. Cross-adaptation and binary mixture experiments suggest that only one olfactory receptive mechanism is involved in PGFs detection. The behavioural and olfactory responses observed with exposure to PGF_2α and its metabolites suggest these compounds function as reproductive pheromones in brown trout and lake whitefish.     

Behavioural responses of two cladocerans and two copepods exposed to fish kairomones

In natural predator–prey interactions, chemical communication is one of the most advantageous strategies for prey organisms because they can anticipate possible harm by means of phenotypic changes. This study compares the changes in the behaviour of four freshwater zooplankton species in the presence and absence of infochemicals from the same predator. The studied organisms are two copepods and two cladocerans living in highly variable freshwater environments. The analysis is focused on two predator defensive behaviours: a pre-encounter and a post-encounter response. First, we analysed the diel vertical migration (DVM) of the organisms inside 150?cm long transparent plastic tubes. Second, we used a novel hydraulic apparatus to quantify their ability to escape from a potential predator. The results revealed that the species have different behavioural patterns in the absence of infochemical. The differences were mainly in the way DVM developed and reflect their life histories and adaptive strategies relative to their natural environment. When faced with kairomones, the escape ability of the organisms was enhanced in all cases and DVM changed, although not always in agreement with the expected patterns. The interaction between each species and the multiple environmental components is discussed.     

Effects of fish chemical cues on tadpole survival

The indirect effects of goldfish chemical cues on tadpole survival and predation by other predators (e.g. dragonfly nymph and crayfish) were tested in a field experiment. Fish chemical cues were found to affect tadpole survival when dragonfly nymphs were present. In contrast, this indirect effect was not detected in the presence of crayfish. The results from the present study found that predators, even without predation, can affect the predatory efficiency of other predators, and that the degree of such an indirect effect may differ among the foraging strategies of predators.     

The Arctic charr story: development of subarctic freshwater fish farming in Sweden

We present an overview of 27 years of experience of domestication and farming of Arctic charr (Salvelinus alpinus) in Sweden. The domestication process included an evaluation of suitable strains for farming, a breeding programme and the study of the biological and behavioural characteristics of the species. Traits of three different Arctic charr populations differing in ecology and appearance were compared during initial 2-year trials under farming conditions. The best-performing population with respect to the growth rate and the lowest frequency of early sexual maturation was a piscivore form and this became the foundation for a breeding programme intended to select for an Arctic charr strain suitable for farming. After 23 years and 7 generations, our selective breeding has resulted in a fast-growing, late-maturing strain much appreciated by farmers. The biological and behavioural characteristics studied included annual and diel locomotor activity, feeding, social and thermal behaviour. Applying our findings in these areas has greatly improved both profits and conditions for the fish. Other investigations have focused on the application and further evaluation of the results from research in practical farming trials, such as evaluation of growth at different farms with different temperature conditions, optimal time and stocking density for start-feeding and evaluation of different feeding schedules. In Sweden, Arctic charr is mainly farmed in net pens situated in nutritionally depleted and extremely unproductive water reservoirs formed by damming rivers to create electric power. Judicious farming of Arctic charr in such reservoirs can restore their nutritional and productivity state to that which existed before regulation. Site selection criteria for Arctic charr farming in such waters have been developed. The development of intensive farming of Arctic charr in Sweden is discussed together with current limitations and future possibilities.     

Behavioural responses of a south-east Australian floodplain fish community to gradual hypoxia

1. Hypoxic conditions occur frequently during hot, dry summers in the small lentic waterbodies (billabongs) that occur on the floodplains of the Murray‐Darling River system of Australia. Behavioural responses to progressive hypoxia were examined for the native and introduced floodplain fish of the Ovens River, an unregulated tributary of the Murray River in south‐east Australia. 2. Given the high frequency of hypoxic episodes in billabongs on the Ovens River floodplain, it was hypothesised that all species would exhibit behaviours that would confer a degree of hypoxia‐tolerance. Specifically, it was hypothesised that as hypoxia progressed, gill ventilation rates (GVRs) would increase and aquatic surface respiration (ASR) would become increasingly frequent. Fish were subjected to rapid, progressive hypoxia from normoxia to anoxia in open tanks. 3. All tested species exhibited behaviours consistent with their use of potentially hypoxic habitats. As hypoxia progressed, GVRs increased and all species, with the exception of oriental weatherloach, began to switch increasingly to ASR with 90% of individuals using ASR at various oxygen concentrations below 1.0 mg O₂ L⁻¹. Australian smelt, redfin perch and flat‐headed galaxias were the first three species to rise to ASR, with 10% of individuals using ASR by 2.55, 2.29 and 2.21 mg O₂ L⁻¹ respectively. Goldfish and common carp were the last two species to rise to ASR, with 10% of individuals using ASR by 0.84 and 0.75 mg O₂ L⁻¹ respectively. In contrast to other species, oriental weatherloach largely ceased gill ventilation and used air‐gulping as their primary means of respiration during severe hypoxia and anoxia. 4. Australian smelt, redfin perch and flat‐headed galaxias were unable to maintain ASR under severe hypoxia, and began exhibiting erratic movements, termed terminal avoidance behaviour, and loss of equilibrium. All other species continued to use ASR through severe hypoxia and into anoxia. Following a rise to ASR, GVRs either remained steady or decreased slightly indicating partial or significant relief from hypoxic stress for these hypoxia‐tolerant species. 5. Behavioural responses to progressive hypoxia amongst the fish species of the Ovens River floodplain indicate a generally high level of tolerance to periodic hypoxia. However, species‐specific variation in hypoxia‐tolerance may have implications for community structure of billabong fish communities following hypoxic events.     

Differential responses of male and female red swordtails to chemical alarm cues

Male and female red swordtails Xiphophorus helleri exposed in the laboratory to swordtail skin extract, fathead minnow Pimephales promelas skin extract and distilled water, significantly decreased activity in response to conspecific skin extract compared to minnow skin extract or distilled water. Moreover, males and females responded differentially to conspecific skin extract. Males tended to occupy the top compartment of the tank, whereas females tended to occupy the bottom compartment and seek shelter more. In a second experiment swordtails reduced activity significantly more in response to swordtail skin extract compared to closely related guppy Poecilia reticulata skin extract, minnow skin extract or distilled water. Swordtails also reduced activity significantly more to guppy skin extract compared to minnow skin and distilled water. However, males and females did not respond differentially to guppy skin extract. This suggests that chemical alarm cues are partially conserved within the Poeciliidae, but the level of response is of lower intensity to heterospecific skin extracts.     

Behavioural responses of young cape gannets Sula capensis to high ambient temperatures

A young Cape Gannet Sula capensis responded to high ambient temperatures in the laboratory by standing, gular fluttering with raised head and open bill, wing drooping, defaecating at a fast rate close to or onto the feet, “paddling”; in the excreta, and increased breathing rate. Standing initially caused a decline in foot temperature which rose with rising ambient temperature. Gular flutter and wing drooping assisted the bird in tolerating heat stress. Reduction in heat‐load occurred when standing on a wet surface, presumably due to evaporative heat loss (of excreta on the feet = urohidrosis) and an enhanced conduction of heat to substrate. Field observations confirmed that young Cape Gannets defaecate onto their feet at high ambient temperatures. This species appears preadapted for this behaviour since it builds a solely guano nest, defaecating onto the rim which is compacted by “paddling”;.