A fascinating aspect of sociality in animals is the decision of a subordinate individual to delay independent breeding opportunities in order to remain within a group. Cooperative Breeding theory (CB) contains a number of hypotheses which attempt to explain this behaviour. However a general explanation has remained elusive, despite numerous studies on various terrestrial taxa. One major obstacle is a lack of studies on marine fishes, which show remarkable diversity in social strategies. To address this knowledge gap, I used CB as a framework to study the evolution of sociality in a group of coral reef fishes of the genus Gobiodon. I conducted a large-scale in-situ comparative study to lay the foundation for experimental tests of CB. First, I developed a social index for each species of Gobiodon at Lizard Island. The length of each fish was measured, as well as coral size, to investigate whether these factors predicted sociality. Second, I compared the level of ecological constraints experienced by both asocial and social species to test one of the key hypotheses of CB, known as the Ecological Constraints hypothesis. This hypothesis examines the idea that the costs of dispersing due to ecological pressures make it more preferable for an individual to delay its dispersal and thereby refrain from independent breeding. To examine this hypothesis, transect counts of groups of each Gobiodon species were usedto compare group size, habitat size and habitat saturation. The majority of species with high social indexes had significant relationships between group size and habitat size. Analysis of the habitat saturation data is currently underway. Examination of differing characteristics between species with high and low social indices may provide insights into the evolution of sociality in these fishes.  This study provides evidence that social species of Gobiodon are ecologically constrained in the maximum sizes that their groups can attain and is an important first step toward revealing how sociality may have evolved in Gobiodon species.