Entropy and Fractal Techniques for Monitoring Fish Behaviour and Welfare in Aquacultural Precision Fish Farming-A Review

In a non-linear system, such as a biological system, the change of the output (e.g., behaviour) is not proportional to the change of the input (e.g., exposure to stressors). In addition, biological systems also change over time, i.e., they are dynamic. Non-linear dynamical analyses of biological systems have revealed hidden structures and patterns of behaviour that are not discernible by classical methods. Entropy analyses can quantify their degree of predictability and the directionality of individual interactions, while fractal dimension (FD) analyses can expose patterns of behaviour within apparently random ones. The incorporation of these techniques into the architecture of precision fish farming (PFF) and intelligent aquaculture (IA) is becoming increasingly necessary to understand and predict the evolution of the status of farmed fish. This review summarizes recent works on the application of entropy and FD techniques to selected individual and collective fish behaviours influenced by the number of fish, tagging, pain, preying/feed search, fear/anxiety (and its modulation) and positive emotional contagion (the social contagion of positive emotions). Furthermore, it presents an investigation of collective and individual interactions in shoals, an exposure of the dynamics of inter-individual relationships and hierarchies, and the identification of individuals in groups. While most of the works have been carried out using model species, we believe that they have clear applications in PFF. The review ends by describing some of the major challenges in the field, two of which are, unsurprisingly, the acquisition of high-quality, reliable raw data and the construction of large, reliable databases of non-linear behavioural data for different species and farming conditions.

Individual identification of inbred medaka based on characteristic melanophore spot patterns on the head

With disease progression, individual differences appear, even in an animal disease model with genetic homogeneity. Therefore, non-invasive long term observation and individual identification is desirable for late-onset diseases. To this end, the natural markings used in ecological studies are preferable to the external invasive markings used in animal husbandry and fisheries management. Here, we propose using the distribution pattern of melanophore spots on the head of an inbred strain of medaka, a small fish model organism with monotonous pigmentation, as biometric identifier. Long term and variation analyses show different patterns whose characteristics can be attributed to individual animals. These findings were also valid in a non-inbred medaka strain and will help individual follow-up of late-onset disease medaka models for the elucidation of the pathogenesis and drug discovery.

Female preference for color-enhanced males: a test of the sensory bias model in medaka, a drab fish

Sexual selection research has long focused on the evolution of female mate preferences. Most of the models that have been developed posit that mate preferences evolve in a mating context. In contrast, the sensory bias model proposes that mate choice preferences arise in a non-mating context, as a by-product of natural selection acting on a female’s perceptual system. Recent research has shown that many species of fishes, from across a large clade including poeciliids, goodeids, and medaka, have a bias for long wavelength (LW) colors (yellow, orange, red) in a non-mating context. Even species that do not have LW-colored ornaments, apparently because they have been lost secondarily, retain this latent bias for LW colors. Here, we predicted that female Oryzias latipes (Japanese medaka), a drab species with a latent preference for LW colors, would show a mate choice preference for males with an artificial secondary sexual trait—a colored stripe added to their flank. We confirmed that females were more responsive to red and orange objects in a non-mating context than to other colors. We also showed that females were less resistant towards males with an LW-colored stripe than to those enhanced with a non-LW stripe and that, for many females, responses towards specific LW colors were consistent across these non-mating and mating contexts. Therefore, our results provide support for the sensory bias model by providing a link between a sensory bias in a non-mating context and a mate choice preference in a drab species like medaka.

Identification of Individual Zebrafish (Danio rerio): A Refined Protocol for VIE Tagging Whilst Considering Animal Welfare and the Principles of the 3Rs

In aquatic ecology, studies have commonly employed a tagging technique known as visible implant elastomer (VIE). This method has not been widely adopted by the zebrafish research community and also lacks refinement with regard to animal welfare. The current paper introduces a new VIE tagging protocol, with the aim of improving existing tagging techniques by placing particular emphasis on the Three Rs. To improve animal welfare and fish survival, we added the use of an analgesic compound (lidocaine) through the marking procedure, followed by after-treatment with antiseptics (melaleuca, aloe vera, and PVP-I as active ingredients) to improve tissue regeneration and healing. The newly improved protocol has been quantitatively evaluated on different populations and age groups of zebrafish. This study will be useful to the scientific zebrafish community and to the wider field including biologist and aquarists, especially in consideration of animal welfare, where tagging techniques are considered as a potential noxious stimulus for fish.

Ethical considerations in fish research

Fishes are used in a wide range of scientific studies, from conservation research with potential benefits to the species used to biomedical research with potential human benefits. Fish research can take place in both laboratories and field environments and methods used represent a continuum from non-invasive observations, handling, through to experimental manipulation. While some countries have legislation or guidance regarding the use of fish in research, many do not and there exists a diversity of scientific opinions on the sentience of fish and how we determine welfare. Nevertheless, there is a growing pressure on the scientific community to take more responsibility for the animals they work with through maximising the benefits of their research to humans or animals while minimising welfare or survival costs to their study animals. In this review, we focus primarily on the refinement of common methods used in fish research based on emerging knowledge with the aim of improving the welfare of fish used in scientific studies. We consider the use of anaesthetics and analgesics and how we mark individuals for identification purposes. We highlight the main ethical concerns facing researchers in both laboratory and field environments and identify areas that need urgent future research. We hope that this review will help inform those who wish to refine their ethical practices and stimulate thought among fish researchers for further avenues of refinement. Improved ethics and welfare of fishes will inevitably lead to increased scientific rigour and is in the best interests of both fishes and scientists.

The Tagging Procedure of Visible Implant Elastomers Influences Zebrafish Individual and Social Behavior

One commonly used method to preserve individual identity in the study of social behavior of zebrafish is through silicone-based visible implant elastomers (VIEs), which represent a safe and durable tagging procedure. While the effects of VIE tagging on welfare and general health have been addressed in detail, whether this procedure influences social behavior remains unclear. In this study, we compared individual and group behaviors exhibited by shoals composed of three individuals: two nontagged and one (focal subject) that was either nontagged (control condition) or sham-, purple-, blue-, or yellow tagged. Traditional behavioral parameters of activity, shoaling, and schooling (speed, polarization, and interindividual distances), along with an information-theoretic measure of social interaction (transfer entropy), were used to study the effect of tagging. Our findings indicate that tagging procedure per se significantly increased individual speed of the tagged subjects and of the group. The tagging procedure also altered the level of interaction between individuals, measured by transfer entropy. Conversely, tagging procedure did not influence shoaling and schooling tendencies. These findings suggest that VIE tagging may elicit some level of stress, which may affect some behavioral responses more than others. We recommend use of alternative methods such as multitracking systems when possible.

Using a robotic fish to investigate individual differences in social responsiveness in the guppy

Responding towards the actions of others is one of the most important behavioural traits whenever animals of the same species interact. Mutual influences among interacting individuals may modulate the social responsiveness seen and thus make it often difficult to study the level and individual variation in responsiveness. Here, open-loop biomimetic robots that provide standardized, non-interactive social cues can be a useful tool. These robots are not affected by the live animal's actions but are assumed to still represent valuable and biologically relevant social cues. As this assumption is crucial for the use of biomimetic robots in behavioural studies, we hypothesized (i) that meaningful social interactions can be assumed if live animals maintain individual differences in responsiveness when interacting with both a biomimetic robot and a live partner. Furthermore, to study the level of individual variation in social responsiveness, we hypothesized (ii) that individual differences should be maintained over the course of multiple tests with the robot. We investigated the response of live guppies (Poecilia reticulata) when allowed to interact either with a biomimetic open-loop-controlled fish robot-'Robofish'-or with a live companion. Furthermore, we investigated the responses of live guppies when tested three times with Robofish. We found that responses of live guppies towards Robofish were weaker compared with those of a live companion, most likely as a result of the non-interactive open-loop behaviour of Robofish. Guppies, however, were consistent in their individual responses between a live companion and Robofish, and similar individual differences in response towards Robofish were maintained over repeated testing even though habituation to the test environment was detectable. Biomimetic robots like Robofish are therefore a useful tool for the study of social responsiveness in guppies and possibly other small fish species.

Artificial Visible Implant Elastomer (VIE) tags of different colour and symmetry do not influence mate choice in a cichlid

Experimental individuals are frequently marked with coloured tags for individual identification. Except for birds, the consequences of such artificial tagging on mate choice have been rarely investigated even though individuals often prefer naturally brightly coloured or symmetrically ornamented mates. We tested whether differently coloured Visible Implant Elastomer (VIE) tags influence female mate choice in rainbow kribs,Pelvicachromis pulcher. Females were allowed to simultaneously choose between a control and a VIE-marked male. The VIE-marked male carried two tags of the same colour (red, blue, green or white) set symmetrically or asymmetrically. Females did not show a preference for or avoidance of males carrying any of the colours compared to control males, no matter if the tags had been set symmetrically or asymmetrically. Although we found no discrimination for or against colour-tags, we highlight the importance of considering potential influences of colour-marks on mate choice in behavioural and evolutionary studies.