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backwaters. Cichlids are tropical in distribution, and the lower Rio Y aquiis the northernmost limit of natural occurrence of this group on the west coast of Mexico. Sinaloan cichlids attain lengths of at least 25 cm and weights of 0.3 kg. Nothing is known of its breeding habits, but most species of this group spawn in spring and summer. Young are aggressively guarded by a parent until large enough to fend for themselves. They then move to quiet vegetated areas to feed and grow. Cichlid species sometimes have highly specialized food habits, but Sinaloan cichlids appear to be generalists, feeding on detrital materials, invertebrates, and aquatic vegetation. Marine Species It would be remiss not to include a few marine components of the fish faunas of these two river basins, especially since aquatic communities of the deltas received essentially no study before they were highly modified or essentially destroyed by upstream developments. Most fish species from the Gulf of California scarcely penetrated the Colorado River upstream past the zone of tidal influence. Only stri ped mullet/lisa and Pacific ten pounder/ machete moved far inland. The giant totoaba/totoaba (Fig. 71), endemic to the upper Gulf of California, spawns in the Colorado River estuary, and was an important commercial fish in the past. It has almost disappeared due to overfishing and likely as a result of changes following construction of mainstream dams in the United States. A substantially larger marine fauna existed on the Rio Yaqui delta. Striped mullet (Fig. 72) are common, and comprise a major resource for Mexican fishermen. Other kinds of mullets are present, reflecting the tropical influences in this more southern fauna. Sea trouts are present, and snooks come into distributaries and move as far upstream as the dam at Presa Alvaro Obregon, more than 100 km from the sea. Machete also is present, as are two marine catfishes. The most upstream record for striped mullet in the Colorado River is near Blythe, California, about 300 km from the sea. Pacific tenpounder (Fig. 73) moved about half that distance, to near Yuma, Arizona. Both occupied the Salton Sea after it filled in 1905-07, but disappeared after a few years, presumably due to lack of reproductive success. Both species now move upstream in the Rio Yaqui to the insurmountable dam forming Presa Alvaro Obregon. There is no information on their distributions prior to construction of that dam. Machete rarely exceed 36 cm long in the lower Colorado River, but they achieve 91 cm or more in length in the sea. Its major prey are small plankton- feeding fishes such as anchovies that school in rich estuarine areas. Striped mullet form a substantial part of the fish fauna in mouths of major tropical and subtropical rivers worldwide. They remain an important component of the deltaic fish community of the lower Colorado River, feeding mostly on detritus, finely divided organic materials that accumulate in quiet places. Mullet typically spawn in the sea, and Figure 71. This photograph of a totoabaltotoaba being handled on a research vessel provides a perspective of the size of this giant endemic of the Gulf of California. Photograph provided by J. R. Hendrickson. ~ 36