Exploring Animal Behavior in the Laboratory: Territoriality in Cichlids

Territoriality and the factors that influence the outcome of animal contests are easy to study in a lab using convict cichlid fish (Archocentrus nigrofasciatus). I present a two-week laboratory experiment suitable for high school and college students. In the first week, students observe resident and intruder convict cichlids interacting in the presence of flowerpot territories, allowing them to develop hypotheses about factors that might determine the outcome of contests over resources, including relative size of competitors (“resource holding potential” hypothesis) and ownership (“resource value” hypothesis). They then work with their teacher to design and set up an experiment to test these two hypotheses, providing specific predictions that would support each hypothesis. In the second week, students observe contests between each owner and a larger or smaller intruder. The winner is defined as the individual that spends the most time in the pot and bites more. Students graph their data and decide what statistics are most appropriate for analyzing their results. They determine which hypothesis is supported by their findings and present their findings in scientific paper format.

Diplomonad caused infection in aquarium fish in Serbia

Although commensals in digestive tract of a large number of fish species, diplomonads represent very significant opportunistic pathogens. For so far unknown reasons, they can proliferate uncontrollably and thus cause changes in the skin and internal organs in aquarium fish. The problem is confusion over nomenclature of the two most important genera: Spironucleus i Hexamita. Aquarium fish species in which there were diagnosed changes in the skin caused by diplomonads were: Microgeophagus ramirezi, Apistogramma cacatuoides, Apistogramma nijsseni, Symphysodon aequifasciatus, Pterophyllum altum, Archocentrus nigrofasciatus, Pelvicachromis pulcher i Labidochromis caruleus. The fish were treated with 250 mg tablets of metronizadole dissolved in water, or metronizadole in a concentration of 6.6 mg per liter of water. The treatment was successful in only 9 out of 45 treated fish. In the others the symptoms reappeared after certain time. It is necessary to determine the prevalence of the infection in aquarium fish in Serbia, and also examine the success of the treatment with metronizadole applied in food or even other possibilities of the treatment.

Habitat structure directly affects aggression in convict cichlids Archocentrus nigrofasciatus

Aggressive behavior can be an important factor in determining how animals use and divide space and resources. Previous studies have shown that aggression in fishes can be influenced by a variety of factors, including water temperature and resource levels. In this study, we tested if the amount of habitat structure in the environment affected aggression levels in female convict cichlids Archocentrus nigrofasciatus. We performed a laboratory experiment in which we placed female convict cichlids into an aquarium with low or high amounts of habitat structure and monitored the dominant female's behavior toward the subordinate female. Aggressive behavior in convict cichlids primarily consists of chases and bites. We found that the total time the dominant female spent chasing the subordinate female was greater when there was a low amount of habitat structure as compared to when there was a high amount of habitat structure. We also found that both the average duration of a chasing bout and the number of bites directed at the subordinate fish increased when there was a low amount of structure, but the number of chases did not. These results indicate that increased habitat structural complexity decreases aggressive behavior in convict cichlids.

Convict cichlids benefit from close proximity to another species of cichlid fish

The coexistence of species with overlapping resource use is often thought to involve only negative fitness effects as a consequence of interspecific competition. Furthermore, the scarce empirical research on positive species interactions has predominantly focused on sessile organisms. Here, I experimentally assessed the effect of close proximity of a potential brood predator and competitor on reproductive success of a neotropical cichlid fish. I demonstrate that convict cichlid ( Archocentrus nigrofasciatus ) broods have a higher survival rate near territories of the Nicaragua cichlid ( Hypsophrys nicaraguensis ), and that escape from predation and nest takeovers is the most likely explanation for the decreased offspring mortality.

Aggression, sex and individual differences in cerebral lateralization in a cichlid fish

Cerebral lateralization is an evolutionarily ancient adaptation, apparently ubiquitous among vertebrates. Despite demonstrated advantages of having a more lateralized brain, substantial variability in the strength of lateralization exists within most species. The underlying reasons for the maintenance of this variation are largely unknown. Here, we present evidence that the strength of lateralization is linked to a behavioural trait, aggressiveness, in the convict cichlid ( Archocentrus nigrofasciatus ), and that this relationship depends on the sex of the fish. This finding suggests that individual variation in behaviour may be linked to variation in cerebral lateralization, and must be studied with regard to the sex of the animal.