ABSTRACT
There are groups of teleost fi shes that spend their entire lives in Fresh Waters (FW), while other groups of teleost fi shes spend their entire lives in Sea Water (SW). These two groups, the stenohaline teleosts (stenohaline freshwater and stenohaline marine) are said to constitute the majority of all teleost fi shes (Schultz and McCormick 2013). The remaining small fraction (< 10%) of teleost fi shes is composed of those species that have the capabilities of moving between FW and SW environments, the euryhaline fi shes (from the Greek words urus meaning wide and halinos meaning of salt, with fi rst known use of the word in the late 19th century, Oxford Dictionary, 2014, on line). The family Mugilidae, the topic of this book, consists exclusively, or almost so, of euryhaline species. There are presently considered to be 71 valid species that belong to the family Mugilidae, and these are distributed among 20 genera (with two other genera questionable) (Eschmeyer 2014). This family has a worldwide distribution throughout the tropic and temperate zones (e.g., Thomson 1966, 1997, Nelson 2006). Various species of mullets inhabit waters of all salinity levels including fresh, brackish, marine, and even hypersaline waters, of lakes, rivers, estuaries, lagoons, seas, and oceans. The fl athead grey mullet1 Mugil cephalus has a worldwide distribution between latitude 51º N and 42º S, though it is less abundant in the tropics (Briggs 1960, Harrison 2002). Individuals of M. cephalus have been collected at locations spanning most of the range of salinities among surface waters. While all, or nearly all, members of the family Mugilidae have euryhaline capabilities, there is a great deal of variation among species in their degree of euryhalinity, and apparently, amongpopulations of some widely distributed species, e.g., M. cephalus. However, genetic relationships among populations of this circumglobally distributed mullet are still being debated (see Chapter 1-González-Castro and Ghasemzadeh 2015, Chapter 2-Durand 2015, Chapter 15-Rossi et al. 2015).
