Effects of the long-term anosmia combined with vision deprivation on the taste sensitivity and feeding behavior of the rainbow trout <Emphasis Type="Italic">Parasalmo</Emphasis> (=<Emphasis Type="Italic">Oncorhynchus</Emphasis>) <Emphasis Type="Italic">mykiss</Emphasis>

We compared taste preferences, taste sensitivity, and behavior in testing food objects in the group of intact and two groups of sensory deprived rainbow trout Oncorhynchus mykiss yearlings. We demonstrated that long-term anosmia (for 9 months), as well as anosmia (for 9 months) combined with enucleation (object vision deprivation for 4 months), does not change the taste preference of fish for the agar pellets containing amino acids (L-alanine, L-proline, L-histidine, or glycine; 0.1 M). For all groups of fish, the threshold L-alanine concentration in pellets that caused a significant increase in consumption is 0.01 M. We showed that sensory deprived fish change their behavior of gustatory testing, namely, the rate of repeated snaps decreases as well as the pellet retention time in the mouth cavity. These results demonstrate that long-term anosmia combined with a partial vision deprivation does not significantly change the taste preferences and sensitivity in the fish that have no external taste buds. However, the observed reduction in the testing time of food objects and other changes in fish feeding behavior may suggest some functional alterations in the intraoral sensory systems (gustatory and/or tactile).     

Taste preferences,orosensory food testing,and sound production during feeding by the pearl gourami <Emphasis Type="Italic">Trichopodus leerii</Emphasis> (Osphronemidae)

It has been found that the pearl gourami Trichopodus leerii evaluates the quality of food objects (agar–agar pellets with standard size, shape, and color but having different composition) by touching them with their lips without using its long filamentous ventral fins. Orosensory testing is accompanied by repeated grasps?rejections?grasps of the pellets (up to 28 times). Such manipulations become significantly more frequent and the pellet is retained several times longer if the trial ends with ingestion rather than final refusal of the object by the fish. It has been found for the first time that pearl gourami produces clicking sounds while grasping the pellets. The number of sounds is directly related to the number of grasps of the object performed by the fish. Only two (alanine, serine) of 21 amino acids (L-isomers) were attractive to pearl gourami, another 13 acids turned out to be indifferent stimuli, and six acids had a repulsive taste. Pearl gourami was attracted to the taste of sucrose and Chironomidae larvae extract. The addition of citric acid, calcium chloride, and sodium chloride to the pellets did not influence their consumption by the fish. The more attractive the substances contained by the pellets, the longer time is spent by the fish on orosensory testing of the pellet quality.     

The effect of starvation on taste preferences and testing behavior of food items in the carp <Emphasis Type="Italic">Cyprinus carpio</Emphasis>

The present study is aimed at recording changes in taste preferences and behavior related to testing of artificial agar-agar (2%) pellets with free amino acids (21 amino acids, L-isomers, 0.1–0.001 M) in the carp Cyprinus carpio at increasing duration of starvation (2, 12, 18, 24, 72, and 144 h). Two hours after the end of feeding until satiation, the fish manifest a low foraging activity and, in most cases, they do not grasp the offered pellet. Later on, the feeding motivation in fish increases rapidly and up to 24 h of starvation each of the offered pellets is grasped. In the first hours of starvation the fish refuse from consumption of the grasped pellets even with highly attractive taste stimuli (extract of chironomids, cysteine). Up to 24 h of starvation, the fish restore the differentiated attitude to taste properties of amino acids. Of the latter, four amino acids increase, six decrease, and the other 11 do not render significant influence on consumption of pellets. Up to 72 h of starvation, at the background of continuing increase in the absolute level of consumption of pellets of all types, the taste preferences change but weakly. However, up to 144 h of starvation the number of deterrent amino acids was reduced to one (phenylalanine). At increasing duration of starvation, the number of repeated grasping of pellets changes weakly while duration of testing by fish of pellets of most types increases, especially abruptly in the first 24 h. It is assumed that the decrease or complete loss in fish of the negative reaction to substances, initially having aversive taste properties may be considered as the main mechanism providing expansion of the feeding spectrum and/or transfer of fish onto consumption of new items, initially consumed just occasionally or fully avoided.     

Taste preferences and behavior of testing gustatory qualities of food in stone loach <Emphasis Type="Italic">Barbatula barbatula</Emphasis> (Balitoridae,Cypriniformes)

Extraoral and intraoral taste preferences of stone loach Barbatula barbatula to 21 free amino acid (L-isomers) and 4 classic taste substances were established. It was found that most amino acids (19), as well as citric acid and calcium chloride are suppressants, i.e., significantly decrease grasping of artificial pellets. Such action is most typical of cysteine, glutamine, asparagine, and citric acids. The number of deterrent stimuli among the used substances is smaller than that of suppressants. Only aquatic chironomid extract has positive gustatory properties. The remaining substances have no pronounced taste properties. Touching of a pellet by barbels is an obligatory element of behavior of testing by fish of pellet properties always preceding grasping. It was found that the subsequent development of feeding behavior of fish proceeds according to one of the possible behavioral stereotypes of testing by fish of taste properties of food items. The revealed behavioral response stereotypes differ in the number of manipulations performed by fish with a food item (rejections and repeated graspings) and in the duration of its retention. Stereotype selection is determined by the extraoral taste attractiveness of the food item for fish.     

Taste preferences and feeding behavior of three-spined stickleback Gasterosteus aculeatus of populations of basins of the Atlantic and Pacific oceans

The absence of population specificity of taste spectra in fish was confirmed. It was found that the three-spined stickleback Gasterosteus aculeatus of populations of the North (Norway), Baltic (Latvia), and Okhotsk (Kamchatka Peninsula) seas has similar taste preferences to classical taste substances (sodium chloride, calcium chloride, and sucrose—10%; citric acid—5%) and to 21 free amino acids (L-isomers, 0.1–0.001 M). For fish of all populations, glutamine, glutamic and aspartic acids, and alanine have the most attractive taste; cysteine, asparagine, and histidine have slightly less attractive taste. In Baltic Sea and Sea of Okhotsk sticklebacks, relatively not numerous amino acids that cause a significant decrease in pellet consumption—phenylalanine, tryptophane, leucine, and tyrosine—coincide (in the North Sea stickleback, substances with deterrent taste were not revealed). In sticklebacks of different populations, no differences in manifestation of feeding behavior were found, and correlations between different elements of fish response to pellets are similar or close the same. It was shown that intraoral sensory testing of food objects in three-spined stickleback can proceed along two alternative behavioral stereotypes similar in fish of the studied populations. The dependence of stereotypes of intraoral testing on taste qualities of the food object was revealed for the first time.     

Taste preferences and feeding behavior of the stone loach <Emphasis Type="Italic">Barbatula barbatula</Emphasis> (Balitoridae,Cypriniformes) after partial deprivation of circum-mouth external gustatory and tactile receptors

Comparative study of the feeding behavior and gustatory preferences mediated by extraoral and intraoral gustatory reception in the stone loach Barbatula barbatula in the norm and 1–6 months after extirpation of all three pairs of barbels was performed. It was found that partial loss of external gustatory receptors and the sensory deficit caused by it do not lead to any noticeable disturbances of the ability of fish to evaluate taste properties of food objects (artificial agar-agar pellets containing L-isomers of alanine, lysine, cysteine or an water extract of chironomid larvae) and make an adequate decision of their grasping or ignoring and swallowing or refusing. The extirpation of the barbels does not influence feeding behavior related to determination by fish of the taste properties of pellets and completely retains in its ritual an obligatory preliminary examination of the food object using external gustatory reception. It is suggested that external taste buds having different localization are equally capable of providing for fish a preliminary evaluation of the taste properties of the object. After extirpation of the barbels, the efficiency of grasping pellets decreases in fish, which indicates an important role of tactile reception in the determination of the site of location of the food object and in providing of the accuracy of the hunter’s dart in fish with a weak vision development.     

Palatability of stereoisomers and other amino acid derivatives to fish

Using a behavioral approach, it was shown that stereoisomers and other derivatives of amino acids (Ala, Glu, Gln; 0.1–0.01 М) have different palatability to fish (three-spined stickleback Gasterosteus aculeatus). The palatability of L-α-Ala is higher than of D-α-Ala or L-β-Ala, however, L-Glu and D-Glu equally increase the uptake of agar-agar pellets. L-Glu-Na has no stimulatory effect, probably, due to carnivorous feeding type in the three-spined stickleback. Palatabilities of L-Gln and L-Gln-HCl differ considerably. It is assumed that the influence of the configuration and structure of molecules on the palatability of amino acids to fish, as well as their taste preferences, are species-specific. The diversity of taste properties not only of L-, but also D-isomers of amino acids may matter in choosing adequate food objects in fish. Fish feeding behavior during oral sensory testing of artificial pellets, containing amino acids or their derivatives, obeys two alternative stereotypes, differing in the number of repeated manipulations with pellets and duration of the pellet retention time.     

Influence of Insecticides Diazinon and Endosulfan on Taste Reception in Persian Sturgeon <Emphasis Type="Italic">Acipenser persicus</Emphasis> (Acipenseridae)

The present paper studies the effects of sublethal concentrations of two neurotoxic insecticides (diazinon and endosulfan, duration of exposure 48 h) on the taste attractiveness of L-histidine (0.1 M), L-cysteine (0.1 M), and L-asparagine acid (0.01 M) for juvenile Persian sturgeon Acipenser persicus. The study revealed different effects of diazinon and endosulfan on the extraoral and intraoral taste reception in fish. The taste responses determined by the extraoral taste system (frequency of grasping of 50 food pellets for 5 min of trial) following exposure to endosulfan are the same as in the intact specimens. The exposure to diazinon leads to two to fourfold increase in the number of grasping the pellets, while the amino acids become tasteattractive as opposed to the intact specimens. Both insecticides affect the taste responses controlled by the intraoral taste reception. The insecticide-related pathology is expressed either as a sharp (tens of times) decrease in the absolute and relative consumption of all types of pellets or as full rejection of the pellets after their grasping. Furthermore, the intraoral taste properties of amino acids remain the same as in the intact fish.     

The effect of food odor background on gustatory preferences and gustatory behavior of carp <Emphasis Type="Italic">Cyprinus carpio</Emphasis> and cod <Emphasis Type="Italic">Gadus morhua</Emphasis>

It was shown that stimulation by food odor (aquatic extract of food organisms, 10^?2 and 10^?3 g/l) does not cause shifts in gustatory preferences in carp Cyprinus carpio and cod Gadus morhua but modifies gustatory behavior. The level of consumption by carp of control granules and granules with attractive, by taste, L-proline (0.1 M) or deterrent L-lysine (0.1 M) (item by item presentation of granules) and by cod of control granules and granules with indifferent, to it, L-asparagine (0.1 M) (presentation of 10 granules simultaneously) is similar prior to and during olfactory stimulation. In the presence of food odor, the duration of taste testing for most types of granules, as well as the number of repeated graspings of granules with an attractive taste do not change in fish. At the same time, granules with indifferent or repulsive gustatory properties are rejected and repeatedly grasped by fish against the background of food odor more frequently than in water without odor. Olfactory stimulation leads to a considerable increase in the average number of graspings per one grasped granule with an indifferent or repulsive taste. Such behavior manifested by fish in the presence of food odor in response to granules with unattractive gustatory properties is apparently caused by the contradiction between the information coming via different chemosensory canals—olfactory and gustatory. The obtained results indicate that food stimulation caused by food odor in nature can lead to an increase in the actual consumption of only those accessible food items that have an attractive taste for fish.     

The interoceptive cue properties of ghrelin generalize to cues produced by food deprivation

A number of recent studies implicate the gut-brain peptide ghrelin as a putative "hunger signal". Most of these studies, however, rely on either consummatory behavior (in humans or nonhuman animals) or self-report (in humans) to draw conclusions regarding the orexigenic properties of this peptide. The present study employs the deprivation intensity discrimination paradigm to assess the interoceptive sensory properties of ghrelin in rats. In this paradigm, one group of rats was placed in a training context and presented with sucrose pellets when 24 h food deprived, but not when 1 h food deprived (24+ group). A second group was trained using the opposite sucrose-deprivation level contingency (1+ group). Learning in this paradigm was demonstrated by animals approaching the food delivery location more frequently under their rewarded compared to their non-rewarded deprivation condition (prior to actual pellet delivery). After asymptotic performance of this discrimination was achieved, these animals (1 h food deprived) were administered ghrelin or saline, either i.p. (3 or 6 nmol) or i3vt (0.1 or 1 nmol), placed in the training context, and appetitive responses were measured. Testing was conducted in extinction, eliminating confounding effects of food consumption. Results of these tests showed that 6 nmol i.p. ghrelin and 0.1 and 1 nmol i3vt ghrelin all generalized to a state of 24 h food deprivation, indicating that exogenous ghrelin has sensory properties in common with the stimuli produced by 24 h food deprivation. These results support the notion that endogenous ghrelin contributes to an interoceptive hunger cue, and that this may be a mechanism by which ghrelin influences food intake and appetitive behavior.     

Taste preferences and feeding behaviour in the facultative herbivorous fish,Nile tilapia Oreochromis niloticus

Taste preferences in fishes are known mainly for carnivorous species, whereas herbivorous consumers were rarely used in such studies. The main goal of the present study was to evaluate the taste preferences in the herbivorous African cichlid fish, Nile tilapia Oreochromis niloticus. In laboratory settings, the palatability of widely used taste substances (four taste substances that are considered to be sweet, sour, bitter and salty for humans – sucrose, citric acid, calcium chloride and sodium chloride; 21 free L -amino acids; 12 sugars and artificial sweetener Na-saccharin; 0.1–0.0001 M) was evaluated. In each trial, a standard agar pellet flavoured with a substance was offered for fish individually. The consumption of pellet, the number of grasps and the retention time before the pellet was finally ingested or rejected were registered. Overall, 21 of 38 substances were palatable, whereas other substances did not shift consumption of pellets in relation to blank pellets. Pellets containing citric acid, L -cysteine, L -norvaline, L -isoleucine, L -valine, Na-saccharin and D -sorbitol were consumed in >85% of trials. Taste attractiveness of amino acids was highly species-specific and was not associated with the trophic category of the 19 species compared. Moreover, it did not correlate with dietary quantitative requirements of Nile tilapia (r_s = 0.27; P > 0.05). Palatability of sugars for O. niloticus and their sweetness for humans did not correlate as well (r_s = 0.21; P > 0.05); nonetheless, Na-saccharin has the most attractive taste for both O. niloticus and humans. The most palatable amino acids lost their effect if the concentration was lowered to 0.01 M for L -cysteine and 0.001 M for L -norvaline (lower than 242.3 μg and 23.4 μg per a pellet, respectively). Single pellet grasp was characteristic of O. niloticus feeding behaviour (>95% of trials), and this pattern may be related to the social lifestyle of this species. Fish spent 4–8 s on average for orosensory evaluation of pellet edibility. The retention time correlated with the palatability of substances and was significantly longer in trials that ended up with pellet swallowing. It is suggested that prolonged orosensory evaluation of food before swallowing provides a reliable and accurate sensory evaluation, which, in turn, can reduce the probability that inadequate food will be consumed.     

An analysis of avoidance generalization and food preference transitivity in goldfish,Carassius auratus

To examine the effect of novelty in food selection by fishes, goldfish were trained by feeding them on red or green food pellets. Individual fish and fish in shoals of two, three, and five were then given a choice between equal numbers of familiar pellets and novel (yellow) pellets. In experimental groups, the yellow pellets were soaked in 15% quinine hydrochloride to make them unpalatable. Fish were next presented with equal numbers of familiar and a second novel pellet. It was expected that fish would generalize from their experience with the unpalatable pellets and demonstrate avoidance to sampling a second novel food item. However, as groups, neither controls nor experimentals were reluctant to sample the second novel pellets. Also, fish did not eat significantly more familiar than novel pellets when both were palatable. A third set of experiments examined food preference transitivity in which each pellet type was presented alone and in three pair-wise combinations to individual fish. Although red and yellow pellets were preferred over green, they were preferred equally, indicating an absence of transitivity in pellet choice and, perhaps, a “preference” for a mixture of red and yellow pellets.     

The study of sensory bases of the feeding behavior of the African catfish Clarias gariepinus (Clariidae,Siluriformes)

An experimental study of the role of vision and some other sensory systems in the feeding behavior of the African catfish Clarias gariepinus (SL 20–24 cm, weight 80–95 g) was performed. It was shown that catfish similarly efficiently detect pellets of artificial food in the light and in the dark; in the dark, they display a greater preference for liver pieces than for pellets of artificial food of the same size. Blue pellets were most attractive for fish; red pellets, less attractive; and green pellets were the least attractive. Color selectivity is exhibited by catfish in the light at various combinations of pellets of different colors delivered simultaneously, but is lost in total darkness. The data obtained indicate the polysensory basis of the feeding behavior of catfish. In the light, a well-developed visual reception provides not only for a successful search for food, but also for a selective choice of food items by color. The olfactory and taste properties of food are important regulators of feeding under various light conditions. Thus, C. gariepinus, like other euryphagous fish, lacks a profound sensory specialization in the feeding behavior. When environmental conditions change, the role of the leading sensory system may pass from one sense organ to another.     

Sex‐specific prey partitioning in breeding piscivorous birds examined via a novel,noninvasive approach

Piscivorous birds frequently display sex‐specific differences in their hunting and feeding behavior, which lead to diverging impacts on prey populations. Cormorants (Phalacrocoracidae), for example, were previously studied to examine dietary differences between the sexes and males were found to consume larger fish in coastal areas during autumn and winter. However, information on prey partitioning during breeding and generally on sex‐specific foraging in inland waters is missing. Here, we assess sex‐specific prey choice of Great Cormorants (Phalacrocorax carbo) during two subsequent breeding seasons in the Central European Alpine foreland, an area characterized by numerous stagnant and flowing waters in close proximity to each other. We developed a unique, noninvasive approach and applied it to regurgitated pellets: molecular cormorant sexing combined with molecular fish identification and fish‐length regression analysis performed on prey hard parts. Altogether, 364 pellets delivered information on both, bird sex, and consumed prey. The sexes differed significantly in their overall prey composition, even though Perca fluviatilis, Rutilus rutilus, and Coregonus spp. represented the main food source for both. Albeit prey composition did not indicate the use of different water bodies by the sexes, male diet was characterized by higher prey diversity within a pellet and the consumption of larger fish. The current findings show that female and male cormorants to some extent target the available prey spectrum at different levels. Finally, the comprehensive and noninvasive approach has great potential for application in studies of other piscivorous bird species.     

Tool‐like behavior in the sixbar wrasse,Thalassoma hardwicke (Bennett, 1830)

There are only a few documented cases of the use of either tools or substrates (anvils) as pseudotools in fishes. Described here is an anvil behavior of a labrid fish, Thalassoma hardwicke, observed under aquarium conditions. This fish was fed with pellets that are too large to swallow and too hard to break up into manageable bits using jaws only. The observed individual carried a pellet to an anvil to break it up into pieces small enough to be swallowed. This feeding behavior was frequently repeated (observed in detail about 15 times), nearly always successful, and remarkably consistent, suggesting that the rock selected for an anvil is remembered and its functional qualities or other factors may play a part in its choice. These observations agree with evidence for other advanced cognitive abilities in members of the genus Thalassoma and suggest that, for welfare demand, rocks with rough surfaces should be provided to these fish, especially when they receive hard food for variety. Zoo Biol 29:767–773, 2010. © 2010 Wiley‐Liss, Inc.     

Taste preferences and feeding behavior in threespine stickleback <Emphasis Type="Italic">Gasterosteus aculeatus</Emphasis> in marine and fresh waters

Taste preferences of four classic taste substances (NaCl, CaCl₂, and sucrose, all—10%; and citric acid—5%), and 21 free amino acids (L-isomers, 0.1–0.001 M) for adult threespine stickebacks Gasterosteus aculeatus is determined in marine and fresh waters. Gustatory responses were compared in the fish caught in marine and placed in marine water or in freshwater and in the fish caught in a stream mouth during spawning migration and in a closed freshwater water body. Taste preferences of threespine sticklebacks depend little on water salinity. Of amino acids, cysteine, glutamic acid, and aspartic acid are attractive, as well as glutamine for the fish living permanently in fresh water. Differences in the reaction of fish to agar-agar pellets with NaCl, CaCl₂, and sucrose are considered to be insignificant. Maximum changes occur in the attitude of threespine sticklebacks to citric acid whose taste is palatable to fish in fresh water. It is assumed that the components of marine water render a modifying action on gustatory receptors, the function of receptor cell, and influence susceptibility of fish to the taste of citric acid and, probably, of some other substances. The foraging behavior of fish in fresh water is more active, they consume more pellets, make more numerous repeated grasps, and keep pellets longer in the mouth cavity before swallowing or rejection. It is concluded that, in migratory fish, the abrupt change of external osmotic conditions is not accompanied by noticeable changes on taste preferences and the majority of substances retain their gustatory properties.     

Orosensory food testing in fish: Chronology of behavior

The orosensory food testing behavior in fish was studied using the nine-spined stickleback Pungitius pungitius as an example. The patterns of the chronology of manipulations performed by fish in testing food objects were identified. The existence of two stereotypical patterns of feeding behavior was confirmed, and their new characteristics were obtained. The relationship between the responsiveness to food and the predisposition of fish to feeding was revealed.     

Foraging Trade-offs in Fathead Minnows (Pimephales promelas,Osteichthyes, Cyprinidae): Acquired Predator Recognition in the Absence of an Alarm Response

Pike-naive fathead minnows (Pimephales promelas) were fed ad libitum or deprived of food for 12, 24, or 48 h and then exposed to either conspecific alarm pheromone or distilled water and the odour of a predatory northern pike (Esox lucius). Minnows fed ad libitum or deprived for 12 h showed a stereotypic alarm response to the alarm pheromone (increased time under cover objects and increased occurrence of dashing and freezing behaviour); those deprived of food for 24 h showed a significantly reduced alarm response, while those deprived of food for 48 h did not differ significantly from the minnows exposed to a distilled water control. Upon subsequent testing in an Opto-Varimex activity meter, all groups initially exposed to alarm pheromone and pike odour exhibited an alarm response when exposed to pike odour alone. Those initially conditioned with distilled water and pike odour did nor show an alarm response to pike odour alone. These results demonstrate that there exists a significant trade-off between hunger level and predator-avoidance behaviour in fathead minnows and that minnows can learn the chemical cues of a predatory northern pike through association with alarm pheromone even in the absence of an observable alarm response.     

Some evidence of enhanced alimentary motivation in spontaneously hypertensive rats (SHR)

The consumption of a wet mash of biscuits or pellets, outside the home cage, was determined in adult spontaneously hypertensive (SHR) and normotensive (NT) Wistar rats. Rats were deprived of food for 24 h or satiated. Regardless of the testing conditions, SHR showed a higher food interest than NT rats, which was reflected in a shorter latency to start eating, a longer time of eating to the first interval as well as to the 30 sec interval which terminated the trial, and a larger amount of food consumed during the test trial. The speed of eating was greater in SHR. In the competition for food SHR won almost all encounters with NT rats. The mean time of eating by SHR increased over the consecutive encounters up to 90%. These findings indicate that alimentary motivation of SHR was higher than that of NT rats. The results are discussed in terms of hyperreactivity of SHR.     

The influence of the food size,distance and food site on food carrying behavior in rats (Rattus norvegicus)

The behavior to foods in rats (Rattus norvegicus) was investigated in a seminatural enclosure and in a straight alley in the laboratory. In both situations, the size of food (0.045-, 1-, and 3-g pellets were used in the enclosure and 0.045-, 0.2-, 1-, and 3-g pellets in the alley) and distance between food sites and nest site (1.8, 3.6, 5.4, and 7.2 m in the enclosure and 2, 4, and 6 m in the alley) were varied. In both situations, when food was presented in only 1 place, the food carrying behavior increased as the size of food increased from 0.045 to 1-g. One and three g pellets were always carried, regardless of the distance to nest. On the other hand, when multiple food sites were presented in the alley, rats were more likely to carry small pellet from the further food site, whereas large pellet was always carried and were not influenced by the distance. The behavior to foods in the enclosure, however, was not influenced in either food site condition. This might be due to the difference in familiarity to the environment and anxiety from perceived predation risk.