A study published in the most recent issue of the journal Functional Ecology has shown that parental investment and fecundity, and not brain size, are important in determining the success of an invasive fish species.
The paper by John Drake, involved analyzing data (using statistical methods) on establishment success and the geographical region into which fish were introduced, brain mass, wet body mass, parental investment and estimates of minimum and maximum brood size for 39 species of introduced fish obtained from FishBase.
Prior studies, particularly those in birds, have suggested that brain size influences the species' ability to colonize new habitats, particularly if cognition plays a role in establishment.
The author writes: "Introductions of non-indigenous fishes presumably often fail because features of the new environment, particularly prey variety, are different than those to which the organism's life-history has adapted...
"Thus, species exhibiting relatively superior cognition or more plastic behaviour sets (e.g. food selectivity, mechanisms to evade predation) might more rapidly adjust to their new environments."
In an analysis of 133 introductions across 17 fish species, it was found that fecundity was negatively correlated with establishment success, while no effect of relative brain size on establishment success was found.
A similar lack of correlation between relative brain size and establishment success was found for all 39 species in an analysis of a smaller data set.
It was also found that livebearers and egg-guarding species were more successful in being established upon introduction than non-guarding species.
According to the author, "One explanation for the negative association with fecundity is that parental investment might be more important to establishment than fecundity.
"In 126 introductions of 14 species, reproductive behaviours associated with parental investment were significantly associated with establishment success.
"These results suggest that the correlation between brain size and establishment success is not universal."
For more information, see the paper: Drake, JM (2007). Parental investment and fecundity, but not brain size, are associated with establishment success in introduced fishes. Functional Ecology 21, pp. 963"968.