Shelter use of familiar and unfamiliar groups of juvenile European catfish Silurus glanis

Effects of maternal age and environmental enrichment on learning ability and brain size

It is well known that maternal age at reproduction affects offspring lifespan and some other fitness-related traits, but it remains understudied whether maternal senescence affects how offspring respond to their environments. Early environment often plays a significant role in the development of an animal's behavioral phenotype. For example, complex environments can promote changes in cognitive ability and brain morphology in young animals. Here, we study whether and how maternal effect senescence influences offspring plasticity in cognition, group behavior, and brain morphology in response to environmental complexity. For this, juvenile 3-spined sticklebacks from young and old mothers (i.e. 1-yr and 2-yr-old) were exposed to different levels of environmental enrichment and complexity (i.e. none, simple, and complex), and their behavior, cognitive ability, and brain size were measured. Exposing fish to enriched conditions improved individual learning ability assessed by a repeated detour-reaching task, increased the size of the whole brain, and decreased aggressive interactions in the shoal. Maternal age did not influence the inhibitory control, learning ability, and group behavioral responses of offspring to the experimental environmental change. However, maternal age affected how some brain regions of offspring changed in response to environmental complexity. In offspring from old mothers, those exposed to the complex environment had larger telencephalons and cerebellums than those who experienced simpler environments. Our results suggest that maternal effect senescence may influence how offspring invest in brain functions related to cognition in response to environmental complexity.

The impact of providing hiding spaces to farmed animals: A scoping review

Many wild animals perform hiding behaviours for a variety of reasons, such as evading predators or other conspecifics. Unlike their wild counterparts, farmed animals often live in relatively barren environments without the opportunity to hide. Researchers have begun to study the impact of access to hiding spaces ("hides") in farmed animals, including possible effects on animal welfare. The aims of this scoping review were to: 1) identify the farmed species that have been most used in research investigating the provision of hides, 2) describe the context in which hides have been provided to farmed animals, and 3) describe the impact (positive, negative or neutral/inconclusive) that hides have on animals, including indicators of animal welfare. Three online databases (CAB Abstracts, Web of Science, and PubMed) were used to search for a target population of farmed animals with access to hiding spaces. From this search, 4,631 citations were screened and 151 were included in the review. Fourteen animal types were represented, most commonly chickens (48% of papers), cattle (9%), foxes (8%), and fish (7%). Relatively few papers were found on other species including deer, quail, ducks, lobsters, turkeys, and goats. Hides were used in four contexts: at parturition or oviposition (56%), for general enrichment (43%), for neonatal animals (4%), or for sick or injured animals (1%). A total of 218 outcomes relevant to our objectives were found including 7 categories: hide use, motivation, and/or preference (47% of outcomes), behavioural indicators of affective state (17%), health, injuries, and/or production (16%), agonistic behaviour (8%), abnormal repetitive behaviours (6%), physiological indicators of stress (5%), and affiliative behaviours (1%). Hiding places resulted in 162 positive (74%), 14 negative (6%), and 42 neutral/inconclusive (19%) outcomes. Hides had a generally positive impact on the animals included in this review; more research is encouraged for under-represented species.

Stressful Daylight: Differences in Diel Rhythmicity Between Albino and Pigmented Fish

In laboratory experiments, variously colored strains of animals, including those with albino phenotypes, are commonly used. The melanocortin theory suggests, however, that coloration phenotypes alter animal physiology and behavior. Animals with the albino phenotype show photoreceptor degradation associated with lowered visual accuracy, escape reactions, etc., presumably accompanied by prevailing nocturnal activity and lowered aggressiveness. This assumption was tested in small groups of albino and pigmented European catfish, Silurus glanis, during the diel cycle. The frequency of agonistic interactions was observed during mutual contests for shelters, and subsequently, blood plasma, brain, gill, and liver samples were collected to evaluate stress parameters. In an experimental arena with shelters, the light/dark rhythmicity of locomotor activity and aggressiveness of the two phenotypes were comparable; the peak was observed at night, and a lower peak was observed at dawn. In an experimental stream without shelters, the peak of locomotor activity occurred at night for only the pigmented phenotype. In the evaluation of 4 antioxidants and 1 oxidative stress indicator, representing a total of 15 indices, albino fish showed significant rhythmicity for 8 indices, whereas pigmented catfish showed significant rhythmicity for 5 indices. The production of blood stress parameters with the peak during the day occurred only in albino fish. A complex model was fitted with the aim of evaluating the links between behavioral and biochemical indices. Time periodicity was modeled using a sine wave and confirmed parallel courses of agonistic interactions in the catfish groups; the peak at dawn was associated with a 4.08-fold (conf. int. 3.53–4.7) increase in such interactions. The changes in glucose and superoxide dismutase concentrations varied with phenotype, while the effects of cortisol, lactate and catalase did not. In summary, the rhythmicity of locomotor activity and changes in the aggressiveness of catfish were influenced by shelter availability, and the effect of light-induced stress was more apparent in albino fish than in pigmented conspecific fish. The results suggested that laboratory-raised animals with pigmentation patterns naturally occurring in the wild show more reasonable values during experiments than those with an albino phenotype.

Enrichment in a Fish Polyculture: Does it Affect Fish Behaviour and Development of Only One Species or Both?

Physical enrichment of structures has been used for the last decades in aquaculture to improve fish production and welfare. Until now, this enrichment has been practiced in fish monoculture but not in fish polyculture. In this study, we developed a polyculture of two freshwater species (pikeperch and sterlet) in recirculated systems (tank of 2.4 m3) with or without physical structures for enrichment. Two types of structures were used: a cover plank on a part of the tank decreasing the light intensity and vertical pipes modifying the water flow. The experiment was conducted in triplicate for a three-month period with juvenile fishes (143 ± 41 g and 27.3 ± 2.2 cm for pikeperch and 133 ± 21 g and 32.8 ± 1.6 cm for sterlet). Behavioural (space occupation and abnormal behaviours) and morphological (total length, final weight, Fulton condition factor, coefficient of variation of the final weight, percentage of biomass gain and specific growth rate) traits were measured. The pikeperch changed their space occupation and showed a preference for low light areas. Sterlet also changed their space occupation: they did not use the cover and occurred mainly in the part of the tank without enrichment. There was no difference for the frequency of abnormal behaviours for pikeperch and sterlet between the two sets (with or without enrichment). There was no statistical difference between the two sets for all the morphological and growth parameters no matter the species and the rearing modality.

Pupil size variation as a response to stress in European catfish and its application for social stress detection in albino conspecifics

Hormonal changes such as increased cortisol level in blood plasma in response to stress and social environmental stimuli are common among vertebrates including humans and typically accompanied by other physiological processes, such as changes in body pigmentation and/or pupil dilatation. The role of pupil size variation (PSV) as a response to stress have yet to be investigated in fish. We exposed albino and pigmented European catfish to short-term stress and measured changes in pupil size and cortisol level. Albinos showed lower pupil dilatation and higher cortisol levels than did pigmented conspecifics. A clear positive relationship between pupil dilatation and cortisol concentrations was observed for both pigmented and albino specimens, suggesting that PSV can be used as a stress indicator in fish, irrespective of albino’s inability to express social communication by coloring. During the follow-up, we investigated whether a penultimate contest between albino individuals would impact contestants’ social stress during subsequent contact. We observed PSV during the contact of unfamiliar albino catfish with different penultimate experiences (winner (W) and/or loser (L)). Then, the following treatment combinations were tested: WW, WL and LL. Twenty-four-hour contact of two unfamiliar catfish resulted in higher pupil dilatation among individuals with previous winner experience. Among treatment combinations, a WL contest displayed the highest pupil dilatation for winners. PSV reflected socially induced stress in individuals that was accompanied by the “winner” experience and dominancy in albinos. To conclude, the present study validates pupil dilatation as a non-invasive method to evaluate stress level in pigmented as well as albino fish in various contexts.

Review: Assessing fish welfare in research and aquaculture, with a focus on European directives

The number of farmed fish in the world has increased considerably. Aquaculture is a growing industry that will in the future provide a large portion of fishery products. Moreover, in recent years, the number of teleost fish used as animal models for scientific research in both biomedical and ecological fields has increased. Therefore, it is increasingly important to implement measures designed to enhance the welfare of these animals. Currently, a number of European rules exist as requirements for the establishment, care and accommodation of fish maintained for human purposes. As far as (teleost) fish are concerned, the fact that the number of extant species is much greater than that of all other vertebrates must be considered. Of further importance is that each species has its own specific physical and chemical requirements. These factors make it difficult to provide generalized recommendations or requirements for all fish species. An adequate knowledge is required of the physiology and ecology of each species bred. This paper integrates and discusses, in a single synthesis, the current issues related to fish welfare, considering that teleosts are target species for both aquaculture and experimental models in biological and biomedical research. We first focus on the practical aspects, which must be considered when assessing fish welfare in both research and aquaculture contexts. Next, we address husbandry and the care of fish housed in research laboratories and aquaculture facilities in relation to their physiological and behavioural requirements, as well as in reference to the suggestions provided by European regulations. Finally, to evaluate precisely which parameters described by Directive 2010/63/EU are reported in scientific papers, we analysed 82 articles published by European researchers in 2014 and 2015. This review found that there is a general lack of information related to the optimal environmental conditions that should be provided for the range of species covered by this directive.

How does agonistic behaviour differ in albino and pigmented fish?

In addition to hypopigmentation of the skin and red iris colouration, albino animals also display distinct physiological and behavioural alterations. However, information on the social interactions of albino animals is rare and has mostly been limited to specially bred strains of albino rodents and animals from unique environments in caves. Differentiating between the effects of albinism and domestication on behaviour in rodents can be difficult, and social behaviour in cave fish changes according to species-specific adaptations to conditions of permanent darkness. The agonistic behaviours of albino offspring of pigmented parents have yet to be described. In this study, we observed agonistic behaviour in albino and pigmented juvenile Silurus glanis catfish. We found that the total number of aggressive interactions was lower in albinos than in pigmented catfish. The distance between conspecifics was also analysed, and albinos showed a tendency towards greater separation from their same-coloured conspecifics compared with pigmented catfish. These results demonstrate that albinism can be associated with lower aggressiveness and with reduced shoaling behaviour preference, as demonstrated by a tendency towards greater separation of albinos from conspecifics.

Ostracism of an albino individual by a group of pigmented catfish

Physiological and behavioural constraints hinder albino individuals. Albino animals are rare in the wild; this trait is associated with easy detection by predators, non-native or damaged environments, and exclusively aphotic environments in total darkness. The social aspect of albinism is reported only for human beings, and the effect is distinguishable in time and space when social benefits, are used to a limited the extent. Thus far, the social consequences of albinism for animals remain unknown. We used socially established groups of the pigmented catfish, (Silurus glanis), to observe space and temporal distance detachment of albino specimens in laboratory conditions. The albino fish were separated at larger distances from the group than pigmented individuals with the same social status determined by familiarity, and this asymmetry also varied in time. Albinism-related ostracism results in a solitary existence, usually followed by enhanced predation risk. The motivation for an individual's exclusion from a group appears to be the avoidance of the predation risk that increases not only for an odd individual but also for conspecifics within a group. Our findings indicate a role for albinism in behavioural processes related to sociality in a group of conspecifics.

Environmental effects on behavioural development consequences for fitness of captive-reared fishes in the wild

Why do captive-reared fishes generally have lower fitness in natural environments than wild conspecifics, even when the hatchery fishes are derived from wild parents from the local population? A thorough understanding of this question is the key to design artificial rearing environments that optimize post-release performance, as well as to recognize the limitations of what can be achieved by modifying hatchery rearing methods. Fishes are generally very plastic in their development and through gene-environment interactions, epigenetic and maternal effects their phenotypes will develop differently depending on their rearing environment. This suggests that there is scope for modifying conventional rearing environments to better prepare fishes for release into the wild. The complexity of the natural environment is impossible to mimic in full-scale rearing facilities. So, in reality, the challenge is to identify key modifications of the artificial rearing environment that are practically and economically feasible and that efficiently promote development towards a more wild-like phenotype. Do such key modifications really exist? Here, attempts to use physical enrichment and density reduction to improve the performance of hatchery fishes are discussed and evaluated. These manipulations show potential to increase the fitness of hatchery fishes released into natural environments, but the success is strongly dependent on adequately adapting methods to species and life stage-specific conditions.