Introduction

Abstract

The Mesozoic era lasted about 155 million years and ended some 70 million years before the present. During this era three important vertebrate lineages evolved. The land saw the appearance of the endothermic birds and mammals, the waters saw the rise of the teleost fishes. Teleost fishes now dominate both marine and fresh waters. These fishes (and hereafter fishes will refer only to teleosts unless otherwise qualified) are represented by approximately 20000 living species (Table 1.1) and account for nearly half of all vertebrate species (Nelson, 1984). Of the living species about 58% are marine, 41% live in fresh waters and 1% migrate between fresh and salt waters (Moyle and Cech, 1982).