Learning to find the opponent: an ethological analysis of the behavior of paradise fish (Macropodus opercularis) in intra- and interspecific encounters.

In Experiment 1, 15 behavior patterns of male paradise fish (Macropodus opercularis; n = 72) toward a male conspecific, a male of another species, or no stimulus were recorded, both in home and novel situations. In Experiment 2, the same behaviors were recorded in a runway, and the same stimuli were used as reinforcers in the goal box (n = 18). A typical learning curve was seen when the subject found a male paradise fish in the goal box, learning was followed by apparent extinction when another species was found in the goal box, and few signs of learning were seen when the goal box was empty. Performance of the fish in both experiments can be accounted for by a strong aggressive motivation, a less strong but clear general curiosity, and habituation to the experimental procedure. In contrast to recent assertions in the literature, we conclude that aggressive behavior clearly can serve as a reinforcer in an instrumental learning situation.     

Sensitization of escape in female Betta splendens

Following 1 day of cohabitation with a male, female Siamese fighting fish showed heightened escape from male conspecifics (enclosed behind glass). Escape from males was general in that no particular male stimulus was required to provoke female escape. However, female conspecifics remained relatively attractive following exposure to a male. Tactile stimulation of females by males (biting, perhaps) plays some role and may be required in sensitizing females' escape from males. © 1996 Wiley-Liss, Inc.     

Olfactory self-recognition in a cichlid fish

Animal self-cognizance might be of importance in different contexts like territoriality, self-referent mate-choice or kin recognition. We investigated whether the cichlid fish Pelvicachromis taeniatus is able to recognize own olfactory cues. P. taeniatus is a cave breeding fish with pronounced brood care and social behavior. In the experiments we gave male cave owners the choice between two caves in which we introduced scented water. In a first experiment males preferred caves with their own odor over caves with the odor of an unfamiliar, unrelated male. To examine whether self-recognition is based rather on individual or on family cues we conducted two further experiments in which males could choose between their own odor and the odor of a familiar brother and between the odor of a familiar brother and an unfamiliar, unrelated male, respectively. Males preferred their own odor over that of a familiar brother suggesting individual self-referencing. Interestingly, males (at least outbred ones) preferred the odor of an unfamiliar, unrelated male over that of a familiar brother, maybe to avoid competition with kin. We discuss the results in the context of animal self-cognizance. All experiments were conducted with in- and outbred fish. Inbreeding did not negatively affect self-recognition.     

Male versus female Siamese fighting fish as reinforcing stimuli for conspecific males in single- and two-choice operant situations

Two experiments attempted to determine the reinforcing effectiveness of visual exposure to a female versus a male stimulus in male Siamese fighting fish (Betta splendens). This was accomplished by making male or female presentation contingent upon an operant ring swimming response in single- (Experiment 1) and two-choice (Experiment 2) continuous reinforcement operant situations for 1 hr per day. It was found that visual exposure to a female stimulus was behaviorally reinforcing in a way comparable to that typically found in intermale studies. If given a choice, male test subjects were observed to demonstrate a consistent preference for the female as opposed to the male stimulus. The results are discussed in terms of stimulus discrimination and approach-avoidance conflict as differentially elicited by male and female target stimuli.     

Effects of stress and motivation on performing a spatial task

Learning is ubiquitous in the animal kingdom but has been studied extensively in only a handful of species. Moreover, learning studied under laboratory conditions is typically unrelated to the animal's natural environment or life history. Here, we designed a task relevant to the natural behavior of male African cichlid fish (Astatotilapia burtoni), to determine if they could be trained on a spatial task to gain access to females and shelter. We measured both how successfully animals completed this task over time and whether and how immediate early gene and hormone expression profiles were related to success. While training fish in a maze, we measured time to task completion, circulating levels of three key hormones (cortisol, 11-ketotestosterone, and testosterone) and mRNA abundance of seven target genes including three immediate early genes (that served proxies for brain activity) in nine brain regions. Data from our subjects fell naturally into three phenotypes: fish that could be trained (learners), fish that could not be trained (non-learners) and fish that never attempted the task (non-attempters). Learners and non-learners had lower levels of circulating cortisol compared to fish that never attempted the task. Learners had the highest immediate early gene mRNA levels in the homologue of the hippocampus (dorsolateral telencephalon; Dl), lower cortisol (stress) levels and were more motivated to accomplish the task as measured by behavioral observations. Fish that never attempted the task showed the lowest activity within the Dl, high stress levels and little to no apparent motivation. Data from non-learners fell between these two extremes in behavior, stress, and motivation.     

Predictors of dominance in male Betta splendens

The formation of dominance/subordinancy relations in pairs of male Siamese fighting fish was examined in six experiments. Dominant animals typically were those fish that built the largest nests and that attacked an image of a live, displaying male most intensely prior to combat. However, pretest performance on an operant task and reaction to an animal's own mirror image were not useful predictors of subsequent dominance. These findings are consistent with the suggestion that domesticated Bettas have a territorial social strategy that includes both nest-building and fighting behaviors.     

On the choice between eating and aggressive display in the Siamese fighting fish (Betta splendens)

In Expt 1, male Betta splendens were given a choice between food and a mirror image in a T-maze. All fish consistently preferred food. In Expt 2, the choice of fish that lived in the T-maze for the duration of the experiment was compared with the choice of fish that were transferred to the T-maze for each experimental session. Fish that lived in the T-maze consistently preferred food, but fish that were transferred showed a shift in preference toward mirror image. Differential inhibition of hunger and aggression by fear is suggested as the cause of the preference shift.     

Using visual reinforcement to establish stimulus control of responding of Siamese fighting fish (Betta splendens)

Stimulus control of ring swimming was studied with male Siamese fighting fish (Betta splendens) using 2-component multiple schedules in which the components were correlated with the presence or absence of air bubbles in the water. In Experiment 1, either response-independent mirror presentations or extinction was juxtaposed with immediate response-dependent mirror presentations. Rates of ring swimming generally were higher with immediate reinforcement than with either response-independent mirror presentations or extinction. In Experiment 2, different durations of response-dependent mirror presentations were juxtaposed. Generally, higher rates of ring swimming occurred with 15-s than with 0-, 1-, or 3-s durations. Results demonstrate that stimulus control of responding can be established with these fish under several conditions of differential reinforcement.     

Pre-breeding aggression in male and female three-spined sticklebacks (gasterosteus aculeatus)

The reactions of 34 female and 32 male three-spined sticklebacks to a conspecific were observed in the month before the breeding season. Factor analysis indicated that the organization of the response in the two sexes was very similar; in both cases, axes labelled “aggression,” “threat,” “curiosity,” and “sex” emerged, with male fish having significantly higher scores on the first factor and females on the second. Any theory of the causes of aggression in sticklebacks should accommodate these facts.     

Quantity discrimination in female mosquitofish

The ability in animals to count and represent different numbers of objects has received a great deal of attention in the past few decades. Cumulative evidence from comparative studies on number discriminations report obvious analogies among human babies, non-human primates and birds and are consistent with the hypothesis of two distinct and widespread mechanisms, one for counting small numbers (<4) precisely, and one for quantifying large numbers approximately. We investigated the ability to discriminate among different numerosities, in a distantly related species, the mosquitofish, by using the spontaneous choice of a gravid female to join large groups of females as protection from a sexually harassing male. In one experiment, we found that females were able to discriminate between two shoals with a 1:2 numerosity ratio (2 vs. 4, 4 vs. 8 and 8 vs. 16 fish) but failed to discriminate a 2:3 ratio (8 vs. 12 fish). In the second experiment, we studied the ability to discriminate between shoals that differed by one element; females were able to select the larger shoal when the paired numbers were 2 vs. 3 or 3 vs. 4 but not 4 vs. 5 or 5 vs. 6. Our study indicates that numerical abilities in fish are comparable with those of other non-verbal creatures studied; results are in agreement with the hypothesis of the existence of two distinct systems for quantity discrimination in vertebrates.     

Alcohol and the prior residence effect in male convict cichlids (Cichlasoma nigrofasciatum)

A series of experiments were undertaken to demonstrate the dominance advantage of a territorial resident over an intruder (the prior residence effect) in the adult male Convict Cichlid (Cichlasoma nigrofasciatum) and to evaluate the effects of alcohol (ethanol) on this phenomenon. After successfully demonstrating the prior residence effect, additional experiments were conducted in which the resident or intruder was given one of three different doses of ethanol (0.15%, 0.20%, 0.35%). These doses have previously been shown to reduce or increase intraspecific aggression in this species Over the entire dosage range, drugging the intruder produced no changes in the dominance advantage of the resident. However, drugging the resident at the higher doses (0.20%, 0.35%) resulted in loss of the resident's dominance advantage. These effects were not due to impaired locomotor behavior of the drugged fish, as no abnormal motor behaviors were noted. In general, as reported in previous studies, the resident fish, whether drugged or not, typically attacked first. Also as has been previously shown, the fish that attacked (bit) first typically showed eventual dominance. The present results show that the dominance advantage of the territorial resident is not altered by giving an intruder a hypo- or hyperaggression-producing dose of alcohol. Changes in the dominance advantage occur only as a function of drugging the resident, thereby providing evidence that the behavior of the territorial resident is either directly or indirectly (reaction of the intruder to these changes) responsible for the prior residence effect. The present studies also provide some pharmacological approaches for determining the variables important in a laboratory analog of a naturally occurring instance of intraspecific aggression.     

The biological function of Pavlovian conditioning: Learned inhibition of aggressive behavior in territorial fish

Following Pavlovian discrimination training, stimuli predicting the appearance of a territory intruder (an excitatory conditional stimulus, CS+) or the absence of that event (an inhibitory conditional stimulus, CS−) were presented to pairs of territorial male fish immediately before their first aggressive interaction. Pairmates that both received excitatory stimuli prior to the confrontation were significantly more aggressive than a control group which received the same training but which received neither a CS+ nor a CS− in the test. Pairmates in which both received a CS− were significantly less aggressive than the control group. In these three groups, no differences in aggression were observed between the individual members of a single pair. Two additional groups were composed of pairs whose members received different stimuli prior to the test. Although no differences were found between pairmates in the group in which one member received a pretest CS− while the other member received no stimulus presentation, large differences in aggressive behavior were obtained when one fish received a CS+ and its pairmate received a CS−. We discuss the behavioral ecology of terriorial behavior in fish and attempt to show the potential importance of these results in this naturalistic context. In addition, we discuss the implications of an ecological approach for causal analyses of inhibitory learning.     

A Cue Utilization Approach for Investigating Harvest Decisions in Commons Dilemmas

Hierarchical linear modeling (HLM) is introduced as a new tool for investigating decision making in commons dilemmas. University undergraduates ( N  = 171) managed a virtual fishery, with 2 computer-simulated fishers, over 60 seasons. Level 1 HLM analyses revealed that participants took significantly more fish during seasons when feedback suggested fish stocks, fish value, and fishing expenses were high; and when noncooperative and cooperative others had taken more fish and fewer fish, respectively, in the previous season. Level 2 analyses produced several cross-level interactions, indicating that participants' use of feedback information varied as a function of their social values and environmental attitudes.     

A long‐term fatty fish intervention improved executive function in inpatients with antisocial traits and a history of alcohol and drug abuse

The aim of the present study was to investigate the effects of fatty fish consumption on cognitive functioning in a group of inpatients characterized by antisocial behavior. Eighty‐three male forensic inpatients participated in this study. Participants were randomly assigned into a Fish or a Control group (e.g., meat, chicken, pork). One decision‐making task, the Iowa Gambling Task (IGT), and one planning task, the Tower of Hanoi (ToH), were administered before (pre‐test) and at the end of the intervention period (post‐test). For the IGT the Fish group showed improved performance from pre‐ to post‐ test. Moreover, the Fish group showed significantly better performance than the Control group on the IGT at post‐test. The Fish group also demonstrated improved performance from pre‐ to post‐test on the ToH; however, this was limited to participants with a history of substance abuse. Further, the improvement was only significant for tasks with high working memory load (5–7 move problems), and not for tasks with low working memory load (1–4 move problems). The Control group showed no improvement on any of the tasks regardless of alcohol or drug abuse history. The present study suggests that regular fatty fish consumption may improve executive functions in forensic inpatients with antisocial traits and a history of substance abuse. Thus, the current results may have important implications with regard to health care interventions.     

Effect of telencephalon ablation on the reinforcing and eliciting properties of species-specific events in Betta splendens

In male Betta splendens, aggressive behavior is drastically attenuated following telencephalon ablation. Because instrumental training and Pavlovian conditioning experiments with intact fish have suggested that associative factors may play an important role in the performance of agonistic behaviors, the effect of ablation on instrumental learning and Pavlovian conditioning was studied. In Experiment 1, ablation had no effect on the learning of the instrumental tunnel-swimming response reinforced by mirror presentation (i.e., viewing a conspecific), although the mirror presentations in yoked-control groups elicited fewer responses in ablates than in normal and sham-operated control fish. Yoked controls further established that instrumental responding was maintained by the reinforcement contingency and was not merely the result of increased motor activity. Experiment 2 studied Pavlovian conditioning of the components of the agonistic display. Unconditioned fin erection, gill erection, and tail beating (i.e., unconditioned responses, URs) to the mirror US all were less frequent in ablates than in normals or shams. Of these, only gill cover erection showed evidence of true conditioning (i.e., conditioned responses; CRs) in which responses to the conditioned stimulus (CS) are due to the pairings of CS and US (unconditioned stimulus). However, ablates suffered no impairment of conditioned gill erections. Ablates performed fewer fin erections to the CS; however, fin erection responses were not due to CS-US pairings but were attributable to pseudoconditioning. These results are related to hypotheses postulating the involvement of learning mechanisms in ablation-produced deficits and normal aggressive behavior.     

External inhibition in a goldfish(carassius auratus) classical conditioning situation

Goldfish were classically conditioned with a light as the CS and shock as the US. The UR was a decrease in respiration. After 15 or 60 conditioning trials the fish were tested with novel stimuli (clicks) during the CS-US interval. High and moderate intensity novel stimuli produced a significant decrease in CRs (external inhibition) for fish with 60 conditioning trials (5.5 or 10.5 sec CS-US interval), but not fish with 15 conditioning trials. Low intensity novel stimuli produced no evidence for disinhibition (an increase in CRs). Control groups(e.g., groups with random presentations of the CS and US) showed that the external inhibition for fish with 60 conditioning trials was inhibition of a true CR.     

Effect of anosmia on reproduction in male and female wolves (Canis lupus)

Anosmia was produced in two female and three male wolves by transection of the olfactory peduncle and was confirmed by their inability to detect meat, urine, feces, anal-gland secretions, and fish emulsion. All operated animals continued to investigate the environment with their noses, to interact normally with other pack members, and to feed at levels which maintained presurgical body weights. No effect was found on reproductive physiology (females: estradiol or progesterone concentrations, ovulation, pregnancy or parturition; males: testosterone, testicular recrudescence or sperm numbers, motility or maturation). One anosmic female became dominant and although she urine-marked with a flexed leg, the rate was lower than typical for dominant females and perhaps contributed to her failure to pair-bond with the dominant male. One anosmic male raised-leg-urinated while competing for pack dominance and when kenneled away from other males. Precopulatory, copulatory, and maternal behavior were observed for one anosmic female and appeared normal. However, neither male that was sexually naive before surgery showed interest in proestrous or estrous females. The possibility that secondary degeneration of brain regions mediating sexual behavior was responsible for the failure of these males to respond was not supported. Not only was the lack of male sexual response the only serious deficit following transection, but the male which was sexually experienced prior to surgery did copulate successfully during his second postoperative breeding season despite continued anosmia. Chemosensory priming from female urine during the protracted proestrous phase, as well as urinary and vaginal odors during estrus, appear to be critical for induction of full sexual potency in sexually naive males. The importance of urine and vaginal secretions in the sexual response of experienced males is uncertain.     

Socially mediated learning in male Betta splendens

Seven experiments showed that in the absence of social stimulation male Siamese fighting fish would approach any of several visual and spatial cues that had previously been paired with the animals' mirror images. These findings demonstrate that learned modifications of swimming mediated by social stimuli are possible in Bettas. The present results also suggest that territorial defense in some teleosts may, in part, be mediated by the association of social cues with visual and spatial stimuli.     

Habituation, sensitization, and redirection of aggression and feeding behavior in the three-spined stickleback (Gasterosteus aculeatus L.)

Three-spined stickleback males maintained in individual aquaria built nests and defended the entire aquarium as a territory. Adjacent compartments containing another male stickleback, a gravid female, or a nongravid female provided a social context within which to study the habituation and sensitization of aggression elicited by a conspecific male intruded into the subject's territory. Typical sensitization-habituation curves were found for all fish regardless of the kind of neighbor. However, behavior redirected as a result of the stimulation of the intruded male differed between conditions. The group with a male neighbor showed increased aggression toward the neighbor, the group with a gravid female neighbor showed courtship, and the group with nongravid female showed neither. A third behavior, nest building, showed no difference between conditions, a result providing little evidence for a simple explanation in terms of general arousal. A second experiment elicited the same motor response to the intruded stimulus, but the motivational category was changed by eliciting the behavior by presenting live brine shrimp. In this experiment, aggression did not change during habituation, but the waning predation was redirected to another food-securing behavior, picking at the substrate. The results provide evidence for the important role that social context plays in understanding the redirection of behaviors, a phenomenon predicted from an extension of the dual-process theory of habituation.     

Trace classical conditioning in rainbow trout (Oncorhynchus mykiss): what do they learn?

There are two main memory systems: declarative and procedural memory. Knowledge of these two systems in fish is scarce, and controlled laboratory studies are needed. Trace classical conditioning is an experimentally tractable model of declarative memory. We tested whether rainbow trout (Oncorhynchus mykiss) can learn by trace conditioning and form stimulus–stimulus, as opposed to stimulus–response, associations. We predicted that rainbow trout trained by trace conditioning would show appetitive behaviour (conditioned response; CR) towards the conditioned stimulus (CS; light), and that the CR would be sensitive to devaluation of the unconditioned stimulus (US; food). The learning group (L, N = 14) was trained on a CS + US contingency schedule with a trace interval of 3.4 s. The control group (CtrL, N = 4) was kept on a completely random schedule. The fish that learnt were further trained as either an experimental (L, N = 6) or a memory control (CtrM, N = 3) group. The L group had the US devalued. The CtrM group received only food. No fish in the CtrL group, but nine fish from the L group conditioned to the light. When tested, five L fish changed their CRs after US devaluation, indicating learning by stimulus–stimulus association of the light with the food. CtrM fish retained their original CRs. To the best of our knowledge, this experiment is the first to show that rainbow trout can learn by trace classical conditioning. The results indicate that the fish learnt by ‘facts-learning’ rather than by reflex acquisition in this study.