Fish use landmarks as 'fences'


The concept of a fence to delineate your territory is not foreign to some fish, according to a paper published in a recent issue of the journal Behaviour.

The study by Carl Smith of the University of St. Andrew’s found that territorial male Rosy bitterling (Rhodeus ocellatus) are able to use artificial landmarks to delineate their territories (in the same manner that a fence would serve in human society).

In a series of experiments, the author subjected two male Rosy bitterlings to a treatment with landmarks and one without.

In the treatment without landmarks, two male Rosy bitterlings were placed one on either side in a tank divided by a transparent partition. Each side of the tank was identical to the other in terms of the décor, and the behaviour of the male fish were recorded for 10 minutes after the transparent partition was removed.  

The treatment with landmarks was identical, except for a metal bar coated with blue plastic being placed along the base of the transparent partition and left in place in the tank after the partition was removed.

Two behaviours were recorded; rate of displaying and frequency that each male crossed the midpoint of the aquarium into the half occupied by their rival.

The results of the experiments showed that the male bitterlings crossed the midpoint of the experimental aquarium into the half occupied by their rival significantly more frequently without a territory-demarcating landmark present than with one.  

Males also displayed to rivals significantly more frequently without a territory-demarcating landmark than with one.  

This suggested that male bitterlings would adopt landmarks to mark territorial boundaries and resolve territorial disputes, lowering the costs of territory defence.

For more information, see the paper: Smith, C (2011) Good fences make good neighbours: the role of landmarks in territory partitioning in the rose bitterling (Rhodeus ocellatus). Behaviour 148, pp. 233–246.