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A comparison of fish diversity was carried out among 45 sites within four localities in the Mexican Tropical Western Atlantic (TWA) and Tropical Eastern Pacific (TEP) regions. Several taxonomical and functional diversity indices were considered, and their relationships with the coral cover were investigated in each locality. We found that despite a lower number of species, the localities within the Mexican TEP region had equal or even higher functional diversity than the localities in the Mexican TWA region where sites within the Caribbean Sea appeared particularly poorly diversified. Divergent relationships between fish diversity and coral cover were observed between the two oceanic regions. On the one hand, it tended to be positive in the TWA, and on the other hand, it was negative in the two TEP localities. This contrast may be explained by the low coral species richness and the homogeneous habitat (low structural complexity) provided by a high cover of coral in the TEP. This study highlighted how the fish assemblages can be functionally diversified within the TEP, a region generally considered poorly diversified, and how the relationship between fish diversity and coral cover may vary between oceanic regions. [ABSTRACT FROM AUTHOR]

There is a growing recognition of the need to conserve biodiversity that has been conceptualised in the Convention of Biological Diversity. Maintenance of fish species richness is particularly important, because habitat degradation in inland waters continues to accelerate on a global scale. Here we develop empirical models for predicting fish species richness in natural lakes in various geographical regions of the world. In tropical lakes where fish biodiversity is richer than in temperate lakes, fish species richness can be predicted by a few variables such as lake area and altitude. Low fish species richness in most temperate lakes might be due to the effect of glaciation on colonisation and speciation of fishes. In US, Canadian and northern European lakes, lake acidification is one of the important factors influencing fish species richness. Although limnological characteristics influence fish species richness in temperate lakes, lake area and altitude have greater predictive power. This is in contrast to fish species richness in rivers, which can be reliably predicted by basin area. In the power curves, which describe the relationship between fish species richness and habitat size in lakes and rivers, the exponent is always greater in tropical regions than in temperate regions. Because fish biodiversity is greater in the tropics threats to fish biodiversity through habitat degradation are greater than those in temperate inland waters. [ABSTRACT FROM AUTHOR]