Fluorescent fish are just part of the shoal

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What do transgenic White Cloud Mountain minnows (Tanichthys albonubes) do when they meet their wild-type cousins?

This is the question that Peng Jiang and coauthors from the Pearl River Fisheries Research Institute in Guangzhou, China sought to answer in their study, which was published in a recent issue of the Journal of Fish Biology. 

The authors examined the shoaling behaviour of wild-type male and female White Cloud Mountain minnows in the presence of red fluorescent transgenic conspecifics.

The authors used a tank divided into three with transparent dividers, placing a single wild-type test fish into the central compartment, and recording its preference for joining either a shoal of wild-type conspecifics, or transgenic conspecifics, one of each having been placed in the end compartments.

Jiang and his colleagues then carried out a series of mate choice experiments, in which wild-type test White Cloud Mountain minnows (either male or female) were given the choice between a single wild-type fish and a single transgenic fish of the opposite sex. 

The experiment was conducted in two stages, with the first stage being similar to the shoaling experiment (in which the test fish were kept separate from the stimulus fish) and the second stage in which the fish were free-swimming and allowed to mingle.

In the shoaling experiments, the authors found that while both wild-type male and female fish chose to swim near groups of fish (whether wild-type or transgenic) over an empty compartment, male and female wild-type fish reacted differently when given a choice between a shoal of wild-type fish and a shoal of transgenic fish.  

Wild-type males spent significantly more time near the transgenic shoal, whereas wild-type females showed no preference for either of the shoals. The reason for this difference is unclear, according to the authors.

The results of the mate choice experiments indicated that wild-type female fish showed no preference for either wild-type or transgenic males, but wild-type males preferred transgenic females to wild-type females.  

At first glance, these results suggested that the redder colour of the transgenic female fish may be more attractive to males, but the authors found that the males only preferred the transgenic females in the free-swimming experiments. This implied that the behavioural preference of wild-type males is not due to visual stimuli but to the presence of chemical and tactile information.

Taken as a whole, the results of the study showed that the enhanced red colour of transgenic White Cloud Mountain minnows did not appear to significantly affect signal communication between them and the wild-type fish.  

Although more studies are needed, the implication is that one would expect transgenic fish escaping into the wild to very readily interbreed with wild-type minnows.

For more information, see the paper: Jiang, P, JJ Bai, X Ye, Q Jian, M Chen and XQ Chen (2011) Shoaling and mate choice of wild-type Tanichthys albonubes in the presence of the red fluorescent transgenic conspecifics. Journal of Fish Biology 78, pp. 127–137.