Reduced dosing and liability in methadone maintenance treatment by targeting oestrogen signal for morphine addiction

Methadone maintenance treatment (MMT) is the major tapering therapy for morphine addictive patients. There have gender differences reported in response to MMT. This study discovered that the estrogen‐response element single nucleotide polymorphism (ERE‐SNP; rs16974799, C/T) of cytochrome 2B6 gene (cyp2b6; methadone catabolic enzyme) responded differently to MMT dosing. Oestradiol was associated with high MMT dosing, high enantiomer (R‐ or S‐) of 2‐ethylidene‐1,5‐dimethyl‐3,3‐dipheny‐pyrrolidine (EDDP; methadone metabolite) to methadone ratio and increased drug‐seeking behaviour, implicating oestradiol‐CYP‐EDDP/methadone axis decreasing MMT efficacy. In mouse model, oestrogen mitigates methadone antinociceptive response, facilitates methadone catabolism and up‐regulates methadone‐associated metabolizing enzymes. Oestrogen also ablates chronic methadone administration‐induced rewarding response. Mechanism dissection revealed the CC genotype of CYP2B6‐ERE‐SNP exerts higher ERE sequence alignment score, higher estrogenic response as compared to TT genotype. At last, preclinical study via targeting estrogen signal that tamoxifen (TMX; selective estrogen receptor modulator, SERM) could facilitate the tolerance phase rewarding response of methadone. Strikingly, TMX also reduces tapering/abstinence phases methadone liability in mice. In conclusion, this study demonstrates altering methadone metabolism through targeting estrogen signals might be able to free morphine addictive patients from the addiction of opioid replacement therapy. Therefore, the add‐on therapy clinical trial introducing SERM in MMT regimen is suggested.     

A phylogenetic approach to the evolution of fish behaviour

Summary WHAT HAVE WE LEARNED?As I indicated in the introduction, this is a non-traditional review. I have not asked What generalizations can we draw about the evolution of fish behaviour based upon information gleaned from phylogenetically based studies? Instead, I have presented detailed discussions of those studies. The reason for this approach is quite simple: if all studies in such a wide area of investigation can be discussed at length in one relatively short paper, then the database is not large enough to warrant the move from information collection to information synthesis. The purpose of this review, then, has been to capture the enthusiasm of the phylogenetically orientated fish ethologists and to highlight their discoveries, in the hopes that this will stimulate further research. If successful, the next review of phylogeny and the evolution of fish behaviour will follow a more familiar pathway.Although the database does not allow us to draw generalizations about the evolution of specific behavioural characters in fishes, the studies to date have uncovered a number of more general evolutionary insights. First, phylogenetic conservatism is evident at all levels of analysis, from the muscle activity patterns that underlie behavioural characters (Lauder 1986; Westneat and Wainwright, 1989; Westneat 1991; Wainwright and Lauder, 1992) through foraging preferences (Winterbottom and McLennan, 1993) and egg deposition strategies (Johnston and Page, 1992) to parental care (Stiassney and Gerstner, 1992). This conservatism forms the backbone against which the appearance of novel behaviours (apomorphies) can be highlighted. Each species' behavioural repertoire is thus a unique combination of very old (plesiomorphic), relatively old (synapomorphic) and recently derived (autapomorphic) characters. Second, phylogenetic analysis has allowed us to investigate models of behavioural evolution that were constructed from a variety of microevolutionary fitness parameters. The macroevolutionary patterns have corroborated some parts of those models (transition from biparental to female-only care: Gross and Sargent, 1985; Stiassney and Gerstner, 1992; transition from fresh water to anadromy: Gross et al., 1988; Stearley, 1992) and highlighted other parts of the models that would benefit from a re-examination of the basic assumptions (transition from biparental or female-only to male-only care: Gross and Sargent, 1985; Stiassney and Gerstner, 1992). Third, expanding our evolutionary perspective to include clades of organisms has allowed researchers to formulate new theories of behavioural evolution incroporating information about the patterns of character origin and diversification as well as information about character maintenance (Ryan, 1900a; Ryan and Rand, 1990; Ryan et al., 1990a). And finally, examination of macroevolutionary correlations between the origin and diversification of behavioural characters has allowed us to make predictions about the forces influencing the evolution of those characters that can then be tested experimentally (McLennan et al., 1988; Basolo, 1990a,b, 1991; McLennan, 1991). The studies presented in this paper have spanned a wide theoretical arena. They have revealed a number of interesting insights about the evolution of behaviour, and in so doing, have demonstrated the hybrid vigour of a research programme based upon integrating phylogeny and experimental ethology, phylogeny and functional morphology, and phylogeny and behavioural ecology. The question to be answered now is:WHERE DO WE GO FROM HERE?If this fledgling research programme is to remain vigorous, we need to do two things. First, channels of communication must be re-opened between systematists and ethologists. Specifically, we need to encourage systematists to construct robust phylogenetic trees for groups of fish that either have already been well studied behaviourally and ecologically, or would be of interest to ethologists if a phylogeny existed (the belontiids, poeciliids, and rivulines come to mind, to name just a few). In the absence of such critical information, behavioural ecologists are faced with the option of investigating their ethological data based upon trees reconstructed from old classification schemes or phenograms, neither of which produces a robust phylogenetic hypothesis of genealogy. Researchers who have opted for this approach preface their investigations with the caveat that the analysis and conclusions are only preliminary because of the unsatisfactory nature of the phylogenetic hypotheses available to them. The importance of a preliminary analysis cannot be understimated for researchers who are frustrated by their inability to apply the phylogenetic approach to their burgeoning data sets. It is, however, critical to remember that a preliminary analysis can, at best, produce only tentative results. If the data themselves are both incomplete and ambiguous, this will compound the problems arising from the absence of a rigorous phylogenetic framework, which will produce a confusing picture of behavioural evolution. It is also important to realize that even the most robust phylogenetic tree is still only a hypothesis of genealogical relationships, a hypothesis that may change with the discovery of new data.Second, links must be forged between comparative ethology and behavioural ecology. All of the examples discussed in this paper uncovered a phylogenetic component in patterns of behavioural origin and diversification. The discovery of this phylogenetic influence, however, is only the first step in developing a comprehensive evolutionary picture because phylogenetic patterns can tell us very little about the processes underlying those patterns. In order to explore questions of process, we must incorporate information about the fitness parameters of behavioural characters into our evolutionary picture. For example, optimizing such parameters onto a phylogenetic tree may allow us to investigate whether there are any macroevolutionary correlations between the origin and divergence of a behaviour and a change in one (or more) of the fitness components. We must also incorporate information about the genetic, developmental and physiological control of behaviour into our comparative framework (Brooks and McLennan, 1991; Willis et al., 1991; Lauder et al., 1993). This is perhaps the most neglected aspect of comparative ethology and will thus be the most difficult to remedy. Details of the genetic and developmental systems underlying behaviour are known for only a handful of taxa and for only a handful of behaviours within those taxa. The physiological control of behaviour is better studied, but has yet to be placed within a phylogenetic context (but see e.g. Stearley, 1992, for an example of the insights that can be gained from such a study). The results of such a multilevel approach will be a more robust estimate of the relative roles for the effects of both phylogenetic heritage and environmental factors in the evolution of behaviour in fishes.     

Three‐spined sticklebacks Gasterosteus aculeatus as a model for exploring behavioural biology

Niko Tinbergen chose the three‐spined stickleback Gasterosteus aculeatus for his classic behavioural studies because they are small, robust, common and easy to house in the laboratory under reasonably natural conditions and also because their behaviour, while sufficiently simple to be tractable, is still sufficiently complex to be interesting. An analysis of citation records shows that this was an inspired choice. Research on these small fish has addressed all four of Tinbergen's famous questions (causation, development, functions and evolution) and has contributed to the understanding of many different behavioural systems. The G. aculeatus literature is used here to explore several themes in fundamental behavioural biology (diet choice, shoaling, behavioural syndromes and sexual signalling) and the extent to which research using G. aculeatus has informed both fundamental and applied behavioural biology, the latter in the context of aquaculture research.     

Methadone enhances the effectiveness of 5‐aminolevulinic acid‐based photodynamic therapy for squamous cell carcinoma and glioblastoma in vitro

Although having shown promising clinical outcomes, the effectiveness of 5‐aminolevulinic acid‐based photodynamic therapy (ALA‐PDT) for squamous cell carcinoma (SCC) and glioblastoma remains to be improved. The analgesic drug methadone is able to sensitize various tumors to chemotherapy. In this in vitro study, the influence of methadone to the effectiveness of ALA‐PDT for SCC (FADU) and glioblastoma (A172) was investigated on the protoporphyrin IX (PpIX) fluorescence, survival rates, apoptosis, and cell cycle phase, each with or without the presence of methadone. The production of PpIX was increased by methadone in FADU cells while it was decreased in A172 cells. The survival rates of both cell lines treated by ALA‐PDT were significantly reduced by the combination with methadone (P < .05). Methadone also significantly increased the percentage of apoptotic cells and improved the effect of ALA‐PDT on the cell cycle phase arrest in the G0/G1 phase (P < .05). This study demonstrates the potential of methadone to influence the cytotoxic effect of ALA‐PDT for both SCC and glioblastoma cell lines.      

Boldness and Information Use in Three‐Spined Sticklebacks

In foraging groups, individuals may utilise information from their social environment to aid decision making when choosing where to search for food. Little work has looked at the costs or benefits of behavioural differences, such as consistent individual variation in boldness, with respect to learning ability. Here, we investigate the response of three‐spined stickleback (Gasterosteus aculeatus) to ‘social cues’, ‘local enhancement’ and ‘public information’ during foraging tasks. Our results confirm previous work suggesting that this species responds to social cues and local enhancement but not public information. Variation in boldness did not affect the use of different types of information. However, time taken to make a choice and reach a patch varied between fish with different levels of boldness. Contrary to expectation, shy fish were the more variable individuals, having a greater range of reaction times when responding to the tasks. This suggests that individual behavioural differences still play a role when utilising information obtained from the environment and may influence the relative benefits that could result in different contexts.     

Yes,correct context is indeed the key: An answer to Haave‐Audet et al. 2019

We published a study recently testing the link between brain size and behavioural plasticity using brain size selected guppy (Poecilia reticulata) lines (2019, Journal of Evolutionary Biology, 32, 218‐226). Only large‐brained fish showed habituation to a new, but actually harmless environment perceived as risky, by increasing movement activity over the 20‐day observation period. We concluded that “Our results suggest that brain size likely explains some of the variation in behavioural plasticity found at the intraspecific level”. In a commentary published in the same journal, Haave‐Audet et al. challenged the main message of our study, stating that (a) relative brain size is not a suitable proxy for cognitive ability and (b) habituation measured by us is likely not adaptive and costly. In our response, we first show that a decade's work has proven repeatedly that relative brain size is indeed positively linked to cognitive performance in our model system. Second, we discuss how switching from stressed to unstressed behaviour in stressful situations without real risk is likely adaptive. Finally, we point out that the main cost of behavioural plasticity in our case is the development and maintenance of the neural system needed for information processing, and not the expression of plasticity. We hope that our discussion with Haave‐Audet et al. helps clarifying some central issues in this emerging research field.     

Rates of Fetal Polydrug Exposures in Methadone-Maintained Pregnancies from a High-Risk Population

Methadone maintenance treatment (MMT) is the standard of care during pregnancy for opioid-dependency, showing efficacy in improving prenatal care and reducing risk of relapse. By design, however, MMT is only intended to prevent withdrawal thus facilitating cognitive behavioural interventions. In order to maximize the benefits of MMT, it is essential that methadone is both properly prescribed and that additional addiction treatment is concurrently administered. This study aims to determine the effectiveness of MMT engagement in high-risk pregnant women in reducing polydrug use by objective laboratory examination of neonatal meconium.

Patients and Methods

Over a 29-month period, the Motherisk Laboratory at the Hospital for Sick Children in Toronto analyzed meconium samples as per request by social services and hospitals for drugs of abuse.

Results

Of the 904 meconium samples received, 273 were tested for methadone with 164 positive and 109 negative for methadone. Almost half of the methadone positive samples (46.34%) were also positive for at least one other opioid compound, which did not differ statistically from the methadone-negative control samples (46.79%; Chi square test, p=0.94). No differences were found between the methadone positive and negative groups in rates of concurrent amphetamines, cocaine, cannabis, and alcohol use indicating a similar risk of polydrug use between pregnant women taking or not taking methadone in this population.

Discussion

The high rates of additional opioid and other drug use in the MMT group, suggest that MMT is failing this population of patients. It is possible that methadone doses during pregnancy are not appropriately adjusted for changes in pharmacokinetic parameters (e.g. blood volume, renal function) during the second and third trimesters. This may result in sub-therapeutic dosing creating withdrawal symptoms leading to additional substance use. Alternatively, these results may be demonstrating a substantial lack in delivery of addiction support services in this vulnerable population.     

Conspecific density and environmental complexity impact behaviour of turquoise killifish (Nothobranchius furzeri)

Fish models are essential for research in many biological and medical disciplines. With a typical lifespan of only 6 months, the Turquoise killifish (Nothobranchius furzeri) was recently established as a time- and cost-efficient model to facilitate whole-life and multigenerational studies in several research fields, including behavioural ecotoxicology. Essential information on the behavioural norm and on how laboratory conditions affect behaviour, however, is deficient. In the current study, we examined the impact of the social and structural environment on a broad spectrum of behavioural endpoints in N. furzeri. While structural enrichment affected only fish boldness and exploratory behaviour, fish rearing density affected the total body length, locomotor activity, boldness, aggressiveness and feeding behaviour of N. furzeri individuals. Overall, these results contribute to compiling a behavioural baseline for N. furzeri that increases the applicability of this new model species. Furthermore, our findings will fuel the development of improved husbandry protocols to maximize the welfare of N. furzeri in a laboratory setting.     

Search for informative polymorphisms in candidate genes: clock genes and circadian behaviour in blue tits

The identification of functional polymorphisms in genes that underlie behavioural trait variation is a challenging but intriguing task in evolutionary biology. Given the wealth of genomic data and the increasing number of genotype–phenotype association studies in model organisms, one can ask whether and how this information can be used for non-model organisms. Here we describe two strategies to search for likely functional polymorphisms in candidate genes in a bird species that has been intensively studied by behavioural and population ecologists, the blue tit Cyanistes caeruleus. In the first approach we searched for repeating elements in coding regions of the genome using information about repeats in Gallus gallus genes. The rationale is that tandem-repeat elements have a high potential to be polymorphic and functional. The second strategy aimed to replicate reported genotype–phenotype association studies by extrapolating results from model organisms to our study species. Both strategies showed high success rates with respect to finding homologous gene regions and potentially informative genetic variants in the genes AANAT, ADCYAP1, CKIε, CLOCK, CREB1, NPAS2 and PERIOD2. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Associations in the midwater zone: The penaeid shrimp funchalia sagamiensis fujino 1975 and pelagic tunicates (order: Pyrosomatida)

An association between the penaeid shrimp Funchalia sagamiensis FUJINO 1975 and pelagic tunicates of the Order Pyrosomatida was confirmed through in situ submersible and shipboard observations. Information on this association, including behavioural, morphological and distributional data is presented. The association is “strong”;, possibly obligate for the shrimp during this life‐history phase, and does not appear to be species‐specific. Further information is presented on the taxonomic standing within the genus Funchalia of the enigmatic species F. sagamiensis. The utility of submersibles for in situ behavioural research is discussed.     

Divergence in brain composition during the early stages of ecological specialization in Heliconius butterflies

During speciation across ecological gradients, diverging populations are exposed to contrasting sensory and spatial information that present new behavioural and perceptive challenges. These challenges may be met by heritable or environmentally induced changes in brain function which mediate behaviour. However, few studies have investigated patterns of neural divergence at the early stages of speciation, inhibiting our understanding of the relative importance of these processes. Here, we provide a novel case study. The incipient species pair, Heliconius erato and H. himera, are parapatric across an environmental and altitudinal gradient. Despite ongoing gene flow, these species have divergent ecological, behavioural and physiological traits. We demonstrate that these taxa also differ significantly in brain composition, in particular in the relative levels of investment in structures that process sensory information. These differences are not explained solely by environmentally‐induced plasticity, but include heritable, nonallometric shifts in brain structure. We suggest these differences reflect divergence to meet the demands of contrasting sensory ecologies. This conclusion would support the hypothesis that the evolution of brain structure and function play an important role in facilitating the emergence of ecologically distinct species.     

Individual Variation in Behavioural Reactions to Unfamiliar Conspecific Vocalisation and Hormonal Underpinnings in Male Chimpanzees

It has been established that various species exhibit personality, defined as intra‐individual consistency and inter‐individual variation in behavioural phenotypes. For example, certain individuals may demonstrate consistently greater behavioural reactions and elevated stress responses. We conducted playback experiments and hormonal analyses on male chimpanzees (Pan troglodytes) in captivity to investigate the patterns and proximate mediators of individual variations in behavioural reactions. We found intra‐individual consistency and inter‐individual variation in behavioural reactions (intensive vigilance towards the direction of speakers) to vocalisations by unfamiliar chimpanzees. This behavioural reaction was positively correlated with changes in salivary cortisol concentration, suggesting that stress is a proximate factor mediating the variation in behavioural reactions. The males who were highly responsive to the conspecific vocalisation also exhibited high behavioural reactions towards the neutral broadcast stimulus (the jungle crow’s Corvus macrorhynchos ‘ka’ vocalisation). This observation is consistent with the notion that male chimpanzees vary in intrinsic behavioural tendency to different stimuli.     

Behavioural effects of temperature on ectothermic animals: unifying thermal physiology and behavioural plasticity

Temperature imposes significant constraints on ectothermic animals, and these organisms have evolved numerous adaptations to respond to these constraints. While the impacts of temperature on the physiology of ectotherms have been extensively studied, there are currently no frameworks available that outline the multiple and often simultaneous pathways by which temperature can affect behaviour. Drawing from the literature on insects, we propose a unified framework that should apply to all ectothermic animals, generalizing temperature's behavioural effects into: (1) kinetic effects, resulting from temperature's bottom‐up constraining influence on metabolism and neurophysiology over a range of timescales (from short to long term), and (2) integrated effects, where the top‐down integration of thermal information intentionally initiates or modifies a behaviour (behavioural thermoregulation, thermal orientation, thermosensory behavioural adjustments). We discuss the difficulty in distinguishing adaptive behavioural changes from constraints when observing animals' behavioural responses to temperature. We then propose two complementary approaches to distinguish adaptations from constraints, and categorize behaviours according to our framework: (i) ‘kinetic null modelling’ of temperature's effects on behaviour; and (ii) behavioural ecology experiments using temperature‐insensitive mutants. Our framework should help to guide future research on the complex relationship between temperature and behaviour in ectothermic animals.     

Seabirds and sandeels: the conflict between exploitation and conservation in the northern North Sea

Sandeels, especiallyAmmodytes marinus are a major component of the diet of many predatory fish, seabirds and seals. The industrial fishery for sandeels is now the largest of the North Sea fisheries. A sandeel fishery in the Shetland area began in 1974 but has recently declined. This change was accompanied by dramatic declines in the breeding success of certain seabirds, particularly Arctic terns and kittiwakes. Current information on seabirds and sandeels in the Shetland area is reviewed and areas where further research is needed, highlighted. The Shetland problem illustrates the difficulties of reconciling conservation and exploitation when fundamental ecological and behavioural knowledge is lacking, and also the need to obtain further information on the ecological impact of industrial fisheries.     

An experimental test of the Jennings hypothesis of behavioural organization

An experimental test of H. S. Jennings’ principle of “selection of overproduced movements” was conducted using a jellyfish (Sarsia tubulosa M. Sars) as the experimental animal. The hypothesis was that behavioural repertoire and diversity (measured as Brillouin's H) would be higher under unfavourable environmental conditions. The results showed no difference in behavioural repertoire and reduced behavioural diversity under unfavourable environmental conditions. The reduction in behavioural diversity was due to lower behavioural evenness under experimental conditions.     

Behavioural and morphological changes in ciliates induced by the predator Amoeba proteus

The predator Amoeba proteus induced behavioural and morphological changes in ciliates of the genus Euplotes. The frequency of avoidance behaviour in E. octocarinatus increased from 16±5% to 84±5% (SD) after 14 h of coexistence with the predator. The ciliate's width increased from 59±3 μm to 77±4 μm (SDM) within 48 h. Similar behavioural, but not morphological, change was induced in E. daidaleos, but neither morphological nor behavioural responses occurred in E. aediculatus. E. octocarinatus and E. daidaleos populations survived in the presence of A. proteus, whereas E. aediculatus populations became extinct by predation. Induced behavioural response seemed to be the reason for the low predation risk of E. octocarinatus and E. daidaleos. The results suggest that Euplotes ciliates have evolved specific defence mechanisms to various predators. Defensive changes are induced by a chemical substance released from A. proteus. This “kairomone” has a molecular weight between 5000 and 10000 Da. Proteolytic digestion of its activity indicated that the avoidance-inducing substance is a peptide. After the turbellarian Stenostomum sphagnetorum had induced a defensive morphology in E. octocarinatus or E. aediculatus, neither of these ciliates immediately avoided Amoeba proteus. Thus, Euplotes ciliates with a defensive morphology do not have behavioural defences in reaction to all predators.     

Behaviour genetics ofDrosophila: Non-sexual behaviour

The analysis of genetic behaviour within and between species provides important clues about the forces shaping the evolution of behavioural genes. Genes can affect natural behavioural variation in different ways. Allelic variation causes alternative behavioural phenotypes, whereas changes in gene expression can influence the initiation of behaviour at different ages. Identifying the genes involved in polygenic traits has been difficult. Chromosomal analysis has been widely used as a first step in elucidating the genetic architecture of several behaviours ofDrosophila. Behavioural genetic and molecular studies helped to reveal the genetic basis of circadian time keeping and rhythmic behaviours. InDrosophila, a number of key processes such as emergence from the pupal case, locomotor activity, feeding, olfaction and aspects of mating behaviour are under circadian regulation. Evolutionary biology considers migration behaviour as central in genetic structure of populations and speciation. Genetic loci that influence behaviour are often difficult to identify and localise in part due to the quantitative nature of behavioural phenotypes. Diapause is a hormonally mediated delayed response to future adverse conditions and can occur at any stage of development in an insect. Diapauseassociated gene expression was studied inDrosophila using subtractive hybridisation. Several approaches have been made to unravel the genetic complexity of the behaviour, which have provided information that may be useful in different ways. There is evidence that species do differ in genetic architecture of photoresponse and this may be related to their natural environment. The classical experiments by Jerry Hirsh and Th. Dobzhansky to know the nature of genetic basis for extreme selected geotactic behaviour in fruit flies constituted the first attempt at the genetic dissection of a complex, polygenic behaviour. Understanding the genetic differences between these selected lines would provide an important point of entry into the study of genetic mechanisms of sensing and responding to gravity, as well as clues to the origins of genetic flexibility and plasticity in an organism’s response.     

Similar recent selection criteria associated with different behavioural effects in two dog breeds

Selection during the last decades has split some established dog breeds into morphologically and behaviourally divergent types. These breed splits are interesting models for behaviour genetics since selection has often been for few and well‐defined behavioural traits. The aim of this study was to explore behavioural differences between selection lines in golden and Labrador retriever, in both of which a split between a common type (pet and conformation) and a field type (hunting) has occurred. We hypothesized that the behavioural profiles of the types would be similar in both breeds. Pedigree data and results from a standardized behavioural test from 902 goldens (698 common and 204 field) and 1672 Labradors (1023 and 649) were analysed. Principal component analysis revealed six behavioural components: curiosity, play interest, chase proneness, social curiosity, social greeting and threat display. Breed and type affected all components, but interestingly there was an interaction between breed and type for most components. For example, in Labradors the common type had higher curiosity than the field type (F_1,1668 = 18.359; P < 0.001), while the opposite was found in goldens (F_1,897 = 65.201; P < 0.001). Heritability estimates showed considerable genetic contributions to the behavioural variations in both breeds, but different heritabilities between the types within breeds was also found, suggesting different selection pressures. In conclusion, in spite of similar genetic origin and similar recent selection criteria, types behave differently in the breeds. This suggests that the genetic architecture related to behaviour differs between the breeds.     

Appetitive conditioning technique reveals behavioural limits to passage performance in fishes

Numerous environmental features have the potential to act as barriers to fishes in the field. Passage of these barriers depends on two main properties: willingness (behavioural) and physiological capacity. The physiological swimming capacity of fishes has been well studied. However, because most barrier research has focused on the population level effects of man – made barriers, little attention has been given to the behavioural aspects of fish passage. We used appetitive conditioning to create a simple laboratory based protocol to estimate behavioural limits to fish passage. We tested our protocol using barrier height (or passage space) as a model. Our protocol successfully identified behavioural limits in two species, juvenile rainbow trout, Oncorhynchus mykiss, and fathead minnows, Pimephales promelas. Our most interesting observation was that even a partial, submerged barrier had the potential to block fish movements. Our results suggest a potential use for conditioning techniques in assessing factors that constitute behaviour barriers to fishes. This information may help us to better predict fish movements in the field and may help us to design barriers that are more efficient at passing fishes.