Behaviour of proactive and reactive tilapia Oreochromis niloticus in a T-maze

Growth and physiological response of proactive and reactive juvenile "tambaqui" (Colossoma macropomum) in a recirculating aquaculture system

This study evaluated the growth and physiological response of proactive and reactive Colossoma macropomum juveniles in a recirculating aquaculture system (RAS). In Phase 1 of the experiment (50 days of cultivation), juveniles, weighing 2.16 ± 0.52 g, were stocked in 12 28-L tanks to test the following treatments: proactive (PT), reactive (RT) and mixed (MT) composed of reactive (MRT) and proactive (MPT) animals. In Phase 2 of the experiment (40 days of cultivation), the animals were transferred to 175-L tanks with the same treatments as Phase 1. The animals were fed twice a day with commercial diet during both phases. After Phase 1, MPT animals showed higher growth than MRT animals (P < 0.05), and higher weight gain and daily weight than PT animals (P < 0.05). After Phase 2, PT animals showed higher weight gain and daily weight gain than RT and MT animals (P < 0.05), as did MPT animals compared to PT animals. Performance for RT animals was superior (P < 0.05) to that of MRT animals. Glucose (P < 0.04) and cholesterol (P < 0.01) were higher for RT animals compared to PT animals. Cholesterol was higher for MPT animals compared to MRT animals (P < 0.01), while plasma protein was lower (P < 0.001). Glucose (P < 0.001) and cholesterol (P < 0.01) were higher for MPT animals compared to PT animals and for MRT animals compared to RT animals (glucose P < 0.02, cholesterol P < 0.01). After 90 days of cultivation, proactive animals cultivated separately presented better performance. When cultivated together, reactive animals experienced a decrease in performance and both stress coping styles showed more signs of stress.

Effect of Population Density on Personality of Crayfish (Procambarus clarkii)

Personality is widely observed in animals and has important ecological and evolutionary implications. In addition to being heritable, personality traits are also influenced by the environment. Population density commonly affects animal behavior, but the way in which it shapes animal personality remains largely unknown. In this study, we reared juvenile crayfish at different population densities and measured their personality traits (shyness, exploration, and aggression) after reaching sexual maturity. Our results showed repeatability for each behavior in all treatments, except for the shyness of females at medium density. There was a negative correlation between shyness and exploration in each treatment, and aggression and exploration were positively correlated in medium- and high-density females. These indicate the presence of a behavior syndrome. On average, the crayfish raised at higher population densities were less shy, more exploratory, and more aggressive. We found no behavioral differences between the sexes in crayfish. These results suggested that population density may affect the average values of behavioral traits rather than the occurrence of personality traits. Our study highlights the importance of considering population density as a factor influencing personality traits in animals and, therefore, might help us to understand animal personality development.

Behaviour of personality-screened juvenile Oreochromis niloticus in different challenges: Bold fish present more exploratory capacity and learning to face imposed challenges

The investigation of cultivation and management techniques that take into account behaviour and animal welfare becomes important due to their direct relationship with animal performance. This study aimed to classify juvenile Oreochromis niloticus by personality and compare their performance at exploration and competition tasks. The new object test was used to select bold and shy animals, which were then tested to see which first approached an object. The food competition test involved placing three feed pellets inside a cylinder and measuring the time taken until the pellet was eaten. The new object test found bold animals with a shorter mean time to approach the object than shy animals approaching 65% of the first object when compared to shy. The food competition test found that the bold animals ingested the first pellet more times and with a shorter average time of ingestion than shy animals, no difference in the second intake, whereas the results for the third were same as those for the first. Shy animals had higher intake of the second pellet. Bold animals explored their environment faster in both challenges, while shy individuals exhibited ability to learn from the challenges imposed in the study.

It Began in Ponds and Rivers: Charting the Beginnings of the Ecology of Fish Cognition

But fish cognitive ecology did not begin in rivers and streams. Rather, one of the starting points for work on fish cognitive ecology was work done on the use of visual cues by homing pigeons. Prior to working with fish, Victoria Braithwaite helped to establish that homing pigeons rely not just on magnetic and olfactory cues but also on visual cues for successful return to their home loft. Simple, elegant experiments on homing established Victoria's ability to develop experimental manipulations to examine the role of visual cues in navigation by fish in familiar areas. This work formed the basis of a rich seam of work whereby a fish's ecology was used to propose hypotheses and predictions as to preferred cue use, and then cognitive abilities in a variety of fish species, from model systems (Atlantic salmon and sticklebacks) to the Panamanian Brachyraphis episcopi. Cognitive ecology in fish led to substantial work on fish pain and welfare, but was never left behind, with some of Victoria's last work addressed to determining the neural instantiation of cognitive variation.

Previous experience alters individual vulnerability to angling of crucian carp (Carassius auratus)

In recreational fisheries, fish often undergo catch-and-release angling, which can lead to an indirect selection response of the behavioral traits of the fish. As individuals experience high-intensity angling activities, individuals learn to avoid being selected for artificial bait again, resulting in a change in the vulnerability to angling of fish, which is partly dependent on the cognitive learning ability of the fish. Here, we examined the relationship between vulnerability to angling and learning in juvenile crucian carp (Carassius auratus) under laboratory conditions. Our study had six angling treatments with each containing different group mates (i.e., the angling stress group, all fish that only experienced repeated angling stress practice for a period of three days; the learning group, all fish that only observed individual in the angling stress group to be angled; the control group, all fish that did not undergo any angling or learning; the mixed Group 1, fish are from the control and learning groups; the mixed Group 2, fish are from the control and angling stress groups; the mixed Group 3, fish are from the learning and angling stress groups), each of which consisted of five replicates). All fish were tested for boldness before and after the previous experiences (i.e., angling stress or learning) test. Our results showed that for the stress group, the total angling time, mean individual angling time and total number of bait touches all increased from Day 1 to Day 3, and the total angling rate decreased during the three days of the angling stress practice. After encountering the previous experiences, fish in the control, stress and learning groups all had increased boldness, as assessed by a shortened percent latency to emerge from the refuge. The change in the percent latency of boldness was higher in the stress group than in the learning group, with the control group being intermediate. Furthermore, no differences in the total angling time and total number of bait touches were detected among the six angling treatments, but the stress group exhibited the longest mean individual angling time and lowest angling rate compared with the other five angling treatments, indicating that angling-stressed individuals greatly decreased their vulnerability to angling after the previous angling stress. Our results show that changes in the vulnerability of crucian carp to angling were related to previous individual angling experience but not to visual social learning.

Behavioural variation between piscivore and insectivore rainbow trout Oncorhynchus mykiss

A proactive-reactive continuum integrating multiple (i.e., 3+) dimensions of animal behaviour has been reported as a major axis of behavioural differentiation, but its stability along a biological hierarchy from individuals to populations remains speculative. Piscivore and insectivore rainbow trout (Oncorhynchus mykiss) represent closely related ecotypes with strong ecological divergence driven by selection for a large-bodied piscivorous lifestyle with fast juvenile growth vs. selection for smaller adult body size and lower growth associated with an insectivorous diet. To evaluate whether differences in behaviour between ecotypes are consistent with a proactive-reactive axis and consistent along a biological hierarchy, the authors examined variation in emergence time from a shelter, exploration, activity and predator inspection among individuals, populations and ecotypes of juvenile piscivore and insectivore rainbow trout O. mykiss. As expected, the faster-growing piscivore ecotype was more proactive (i.e., shorter emergence time, exploration and predator inspection) than the more reactive insectivore ecotype. This behavioural contrast was partly maintained across populations, although activity differences were most pronounced among populations, rather than emergence time. Insectivore fry showed substantial variation in behavioural expression among individuals within populations; by contrast, piscivores showed highly similar proactive behaviours with significantly lower inter-individual variation in behavioural expression, suggesting intense selection on behaviour supporting their faster growth. This work suggests that piscivore and insectivore O. mykiss broadly differ in behaviour along a proactive vs. reactive continuum, and highlights the greater multidimensionality of behavioural expression within the insectivore ecotype. Contrasting behaviours between ecotypes may result from differential selection for slow vs. fast juvenile growth and associated metabolism, and may contribute to adult trophic specialization.

Density-dependent changes in neophobia and stress-coping styles in the world's oldest farmed fish

Farmed fish are typically reared at densities much higher than those observed in the wild, but to what extent crowding results in abnormal behaviours that can impact welfare and stress coping styles is subject to debate. Neophobia (i.e. fear of the 'new') is thought to be adaptive under natural conditions by limiting risks, but it is potentially maladapted in captivity, where there are no predators or novel foods. We reared juvenile Nile tilapia (Oreochromis niloticus) for six weeks at either high (50 g l-1) or low density (14 g l-1), assessed the extent of skin and eye darkening (two proxies of chronic stress), and exposed them to a novel object in an open test arena, with and without cover, to assess the effects of density on neophobia and stress coping styles. Fish reared at high density were darker, more neophobic, less aggressive, less mobile and less likely to take risks than those reared at low density, and these effects were exacerbated when no cover was available. Thus, the reactive coping style shown by fish at high density was very different from the proactive coping style shown by fish at low density. Our findings provide novel insights into the plasticity of fish behaviour and the effects of aquaculture intensification on one of the world's oldest farmed and most invasive fish, and highlight the importance of considering context. Crowding could have a positive effect on the welfare of tilapia by reducing aggressive behaviour, but it can also make fish chronically stressed and more fearful, which could make them less invasive.

Transcriptome analysis reveals novel insights into the response of low-dose benzo(a)pyrene exposure in male tilapia

Despite a wide number of toxicological studies that describe benzo[a]pyrene (BaP) effects, the metabolic mechanisms that underlie these effects in fish are largely unknown. Of great concern is the presence of BaP in aquatic systems, especially those in close proximity to human activity leading to consumption of potentially contaminated foods. BaP is a known carcinogen and it has been reported to have adverse effects on the survival, development and reproduction of fish. The purpose of this study was to investigate if a low dose of BaP can alter genes and key metabolic pathways in the liver and testis in male adult tilapia, and whether these could be associated with biological endpoints disruption. We used both high-throughput RNA-Sequencing to assess whole genome gene expression following repeated intraperitoneal injections of 3 mg/kg of BaP (every 6 days for 26 days) and morphometric endpoints as indicators of general health. Condition factor (K) along with hepatosomatic and gonadosomatic indices (morphometric parameters) were significantly lower in BaP-treated fish than in controls. BaP exposure induced important changes in the gene expression pattern in liver and testis as revealed by both Pathway and Gene Ontology (GO) analyses. Alterations that were shared by both tissues included arachidonic acid metabolism, androgen receptor to prostate-specific antigen signaling, and insulin-associated effects on lipogenesis. The most salient liver-specific effects included: biological processes involved in detoxification, IL6-associated insulin resistance, mTOR hyperactivation, mitotic cytokinesis, spindle pole and microtubule binding. BaP effects that were confined to the testis included: immune system functions, inflammatory response, estrogen and androgen metabolic pathways. Taken together, gene expression and morphometric end point data indicate that the reproductive success of adult male tilapia could be compromised as a result of BaP exposure. These results constitute new insights on the mechanism of action of low dose BaP in a non-model organism (tilapia).

Larviculture of a carnivorous freshwater catfish, Lophiosilurus alexandri, screened by personality type

Considering that each personality type in animals presents distinct physiological and behavioural responses, this study evaluated the efficiency of the Novel Environment test to classify larvae of Lophiosilurus alexandri into bold and shy individuals, which were then investigated for growth, cannibalism and mortality in larviculture of pure and mixed groups. Larvae with an average weight of 24.0±1.7mg and length of 14.1±0.4mm, were subjected to a Novel Environment test to classify their personality type (bold and shy larvae). After the larvae were classified according to personality type, they were subjected to larviculture for 15days. Three treatments were tested: only bold larvae, only shy larvae, and a mixed treatment (bold larvae+shy larvae) at a density for 16 larvae/L, which were fed 3 times a day with Artemia nauplii. After larviculture, there were no differences in the final lengths of larvae of the bold, shy, and mixed treatments (26.9±0.76mm, 26.7±1.00mm, and 26.8±1.24mm, respectively); however, shy larvae possessed weighed less (0.22±0.01g) than the bold and mixed treatments, which did not differ significantly (0.25±0.02g and 0.27±0.02g, respectively). The bold and mixed treatments had the highest cannibalism rate (11.2±5.1% and 23.1±12.3%, respectively). Overall survival was lowest in the mixed treatment (62.5±13.0%), while that of the bold and shy treatments were similar (82.5±9.2% and 86.2±9.2%, respectively). The separation of L. alexandri larvae by traits can ensure a decrease in cannibalism and hence, more productive larviculture.