Understanding fish cognition: a review and appraisal of current practices

Animal Cognition - With over 30,000 recognized species, fishes exhibit an extraordinary variety of morphological, behavioural, and life-history traits. The field of fish cognition has grown...     

Correction to: Effects of reward magnitude and training frequency on the learning rates and memory retention of the Port Jackson shark Heterodontus portusjacksoni

Animal Cognition - In the original publication of the article, the Fig. 4 was erroneously published.     

Food approach conditioning and discrimination learning using sound cues in benthic sharks

The marine environment is filled with biotic and abiotic sounds. Some of these sounds predict important events that influence fitness while others are unimportant. Individuals can learn specific sound cues and ‘soundscapes’ and use them for vital activities such as foraging, predator avoidance, communication and orientation. Most research with sounds in elasmobranchs has focused on hearing thresholds and attractiveness to sound sources, but very little is known about their abilities to learn about sounds, especially in benthic species. Here we investigated if juvenile Port Jackson sharks could learn to associate a musical stimulus with a food reward, discriminate between two distinct musical stimuli, and whether individual personality traits were linked to cognitive performance. Five out of eight sharks were successfully conditioned to associate a jazz song with a food reward delivered in a specific corner of the tank. We observed repeatable individual differences in activity and boldness in all eight sharks, but these personality traits were not linked to the learning performance assays we examined. These sharks were later trained in a discrimination task, where they had to distinguish between the same jazz and a novel classical music song, and swim to opposite corners of the tank according to the stimulus played. The sharks’ performance to the jazz stimulus declined to chance levels in the discrimination task. Interestingly, some sharks developed a strong side bias to the right, which in some cases was not the correct side for the jazz stimulus.     

Laterality influences cognitive performance in rainbowfish Melanotaenia duboulayi

Cerebral lateralization has been suggested to convey a selective advantage to individuals by enhancing their cognitive abilities. Few, however, have explicitly compared the cognitive ability of animals with strongly contrasting laterality. Here, we examined the influence of laterality on learning performance in the crimson spotted rainbowfish, Melanotaenia duboulayi, using a classical conditioning paradigm. We also compared the learning ability of wild caught and captive-reared fish to examine the influence of rearing environment on cognitive performance. Laterality was established by observing which eye fish preferred to use while viewing their mirror image. Subjects were then conditioned to associate the appearance of a red light with a food reward over 7 days. Our results revealed that left-lateralized fish learned the conditioning task faster than right-lateralized. These results provide further evidence that cerebral lateralization can play important roles in cognitive function which likely have diverse fitness consequences for animals in their natural environments.     

Learning and memory in the Port Jackson shark,Heterodontus portusjacksoni

Basic understanding of the fundamental principles and mechanisms involved in learning is lacking for elasmobranch fishes. Our aim in this study was to experimentally investigate the learning and memory capacity of juvenile Port Jackson sharks, Heterodontus portusjacksoni. Sharks (N = 30) were conditioned over a 19-day period to associate an underwater LED light or stream of air-bubbles [conditioned stimulus (CS)] with a food reward [unconditioned stimulus (US)], using three procedures (delay, trace and control). During experiments, the CS signalled at a random time between 180 and 300 s for 30 s (six times per day). For the delay the US overlapped in time with the CS, for the trace the US delivered 10 s after the CS and for our control the US was delivered at random time between 180 and 300 s after the CS. H. portusjacksoni sharks trained in all procedures improved consistently in their time to obtain food, indicative of Pavlovian learning. Importantly, the number of sharks in the feeding area 5 s prior to CS onset did not change over time for any procedures. However, significantly more sharks were present 5 s after CS onset for delay for both air-bubble and light CS. Sharks trained in the delay and trace procedures using air-bubbles as the CS also displayed significantly more anticipatory behaviours, such as turning towards the CS and biting. Sharks trained with the light CS did not exhibit such behaviours; however, trace procedural sharks did show a significant improvement in moving towards the CS at its onset. At 20 and 40 days after the end of the conditioning experiments, some sharks were presented the CS without reward. Two sharks trained in the delay procedure using air-bubbles as the CS exhibited biting behaviours: one at 20 and the other at 40 days. This study demonstrates that H. portusjacksoni have the capacity to learn a classical conditioning procedure relatively quickly (30 trials during 5 days) and associate two time-separated events and retention of learnt associations for at least 24 h and possibly up to 40 days.     

Familiarity with the test environment improves escape responses in the crimson spotted rainbowfish, Melanotaenia duboulayi

Animals that are familiar with their environment have been reported to have greater survivorship for a number of reasons related to their knowledge of the terrain, which they recall from memory. In an initial experiment rainbowfish significantly improved their escape response towards a novel trawl apparatus over a sequence of five runs. Escape latencies were still low during a subsequent exposure 11 months after the initial exposure. While part of the improvement in escape success was certainly due to learning associated with the location of the escape route, it is likely that this was aided by habituation to the tank environment and the experimental protocol. In a follow-up experiment, fish that had been kept in the experimental tank for 3 weeks prior to testing, and had become familiar with the test tank, showed significantly lower escape latencies and escaped more often than fish that were not familiar with the test environment. It is suspected that familiarity with the testing arena decreased stress and enabled individuals to detect novel stimuli and devote more attention to them. These findings have significant implications for experimenters studying aspects of animal cognition, such as learning and memory, in laboratory situations. Accepted after revision: 10 August 2001 Electronic Publication     

Social learning in juvenile lemon sharks, Negaprion brevirostris

Social learning is taxonomically widespread and can provide distinct behavioural advantages, such as in finding food or avoiding predators more efficiently. Although extensively studied in bony fishes, no such empirical evidence exists for cartilaginous fishes. Our aim in this study was to experimentally investigate the social learning capabilities of juvenile lemon sharks, Negaprion brevirostris. We designed a novel food task, where sharks were required to enter a start zone and subsequently make physical contact with a target in order to receive a food reward. Naive sharks were then able to interact with and observe (a) pre-trained sharks, that is, ‘demonstrators’, or (b) sharks with no previous experience, that is, ‘sham demonstrators’. On completion, observer sharks were then isolated and tested individually in a similar task. During the exposure phase observers paired with ‘demonstrator’ sharks performed a greater number of task-related behaviours and made significantly more transitions from the start zone to the target, than observers paired with ‘sham demonstrators’. When tested in isolation, observers previously paired with ‘demonstrator’ sharks completed a greater number of trials and made contact with the target significantly more often than observers previously paired with ‘sham demonstrators’. Such experience also tended to result in faster overall task performance. These results indicate that juvenile lemon sharks, like numerous other animals, are capable of using socially derived information to learn about novel features in their environment. The results likely have important implications for behavioural processes, ecotourism and fisheries.     

Environmental enrichment influences spatial learning ability in captive-reared intertidal gobies (Bathygobius cocosensis)

Animal Cognition - Behavioural plasticity is an advantageous trait for animals living in dynamic environments, and can be induced through learning. While some behavioural traits are innate, others...     

Effects of reward magnitude and training frequency on the learning rates and memory retention of the Port Jackson shark Heterodontus portusjacksoni

Animal Cognition - The development of adaptive responses to novel situations via learning has been demonstrated in a wide variety of animal taxa. However, knowledge on the learning abilities of one...