Prozac impacts lateralization of aggression in male Siamese fighting fish

Fins of Fury or Fainéant: Fluoxetine impacts the aggressive behavior of fighting fish (Betta splendens)

While an extensive literature has demonstrated that the selective serotonin reuptake inhibitor (SSRI) antidepressant fluoxetine, disrupts aggressive behavior in male Betta splendens the behavioral mechanisms underlying this disruption remain unknown. To elucidate the behavioral mechanism underlying fluoxetine, male fish were acutely exposed to a 10 μmol (0.0034578 μg/L) concentration of fluoxetine for 25 days using an ABA design. Male Betta splendens are naturally aggressive fish with well-studied and patterned behavioral responses. Importantly, aggressive behavior in this species can be conditionally primed allowing for examination of motivational components of behavior in addition to motor performance. The present study focused on using female fish as an ecologically relevant prime for eliciting aggressive behavior as a means of examining the motivational and motoric effects of fluoxetine. We found that male courtship with a female was strongly correlated with aggressive responding against a mirror. However, despite the strong correlation male fish were not found to have different levels of aggression or changes in aggressive responding when compared to males not primed with a female. Also, latency was not different between the no female prime and female prime males for either the excitatory mirror condition or inhibitory white wall condition, of which the fish had no preference. However, fluoxetine was found to have profound effects on all males in the study regardless of prime type, with increases in latency for the mirror and white wall and decreases in aggressive responding to the mirror. These results support the hypothesis that fluoxetine impairs aggressive motivation and movement in Betta splendens.

Brain and Behavioral Asymmetry: A Lesson From Fish

It is widely acknowledged that the left and right hemispheres of human brains display both anatomical and functional asymmetries. For more than a century, brain and behavioral lateralization have been considered a uniquely human feature linked to language and handedness. However, over the past decades this idea has been challenged by an increasing number of studies describing structural asymmetries and lateralized behaviors in non-human species extending from primates to fish. Evidence suggesting that a similar pattern of brain lateralization occurs in all vertebrates, humans included, has allowed the emergence of different model systems to investigate the development of brain asymmetries and their impact on behavior. Among animal models, fish have contributed much to the research on lateralization as several fish species exhibit lateralized behaviors. For instance, behavioral studies have shown that the advantages of having an asymmetric brain, such as the ability of simultaneously processing different information and perform parallel tasks compensate the potential costs associated with poor integration of information between the two hemispheres thus helping to better understand the possible evolutionary significance of lateralization. However, these studies inferred how the two sides of the brains are differentially specialized by measuring the differences in the behavioral responses but did not allow to directly investigate the relation between anatomical and functional asymmetries. With respect to this issue, in recent years zebrafish has become a powerful model to address lateralization at different level of complexity, from genes to neural circuitry and behavior. The possibility of combining genetic manipulation of brain asymmetries with cutting-edge in vivo imaging technique and behavioral tests makes the zebrafish a valuable model to investigate the phylogeny and ontogeny of brain lateralization and its relevance for normal brain function and behavior.

Behavioral and immunotoxic effects of Prograf® (tacrolimus) in the male Siamese fighting fish

Siamese fighting fish (Betta splendens) has been extensively exploited in the behavioral and physiological toxicology studies of drugs. Tacrolimus is an immunosuppressant drug largely used in liver and renal transplantations. Here we found that a 7-day exposure of male B. splendens to concentrations of 0.05 and 0.1 µg/mL Prograf® (tacrolimus) caused alterations in aggression and immunity indexes. Tacrolimus exposed fish presented lower opercular display in a mirror test which is indicative of reduced aggression. In addition, serum levels of lysozyme, IgM, alternative complement, and bactericidal activity of subjects exposed to 0.1 µg/mL tacrolimus were lower than those from the control treatment. These results showed the behavioral impairment and immunotoxic impacts of tacrolimus in a model of aquatic toxicology. The results suggest fishes provide a possible model for better understanding of the drug action in vertebrates, and possible consequences for the environment via its effects on non-target organisms in an ecotoxicology context.

Behavioral consequences of dietary exposure to crude oil extracts in the Siamese fighting fish (Betta splendens)

Uptake by fishes of crude oil and its polycyclic aromatic hydrocarbons (PAHs) components occurs via gills, dietary intake, or diffusion through the skin. Dietary exposure to crude oil and its components is environmentally relevant, and induces physiological and morphological disruptions in fish. However, the impacts of crude oil on fish social and reproductive behaviors and thus the possible influences on reproductive success are poorly understood. As a part of their intraspecific interactions, male Siamese fighting fish (Betta splendens) exhibit highly stereotypic behavioral and territorial displays. This makes this species a tractable model for testing crude oil effects on behavior. After 2 weeks of acclimation at 29 °C, male adult betta fish were divided into three groups and fed for 4 weeks with food spiked with water (control), low oil concentrations or high oil concentrations (∑Total PAH concentrations 340, 3960 or 8820 ng/g dw, respectively) to determine subsequent alterations in behavioral displays. Compared with control fish, the aggressive display of "opercular flaring" was significantly increased (P < 0.03, n = 14-16) in oil-exposed fish. Bubble nest building, as well as testis and brain mass, were significantly reduced in treated fish (P < 0.05). Hematocrit of treated groups was increased significantly (P < 0.02) from 21% in control fish to ∼27% in both oil exposure groups. Dietary exposure over a 4-week period to low, relevant levels of crude oil thus leads to an increase in aggressive behavioral displays, a decrease in reproductive activity and additional morphological changes.