The mission of the Desert Fishes Council is to preserve the biological integrity of North America's desert aquatic ecosystems and their associated life forms, to hold symposia to report related research and management endeavors, and to effect rapid dissemination of information concerning activities of the Council and its members.

The Cuatro Ciénegas Basin has been surveyed for fish, snails, plants and terrestrial invertebrates, but there has been no published survey of other aquatic invertebrates. We conducted regional surveys of aquatic macroinvertebrates in June and July of 1999 to determine which abiotic and biotic factors influence their distribution and to understand in which habitats they are potentially important components of the food web. Habitats sampled include lagunas, pozas, rios, canals, and springs. Possible endemic species will be presented. Predatory taxa were Odonata and Megaloptera. Herbivorous taxa were primarily Chironomidae, Ephemeroptera, and Amphipoda. Biotic and abiotic factors influencing abundance and distribution will be discussed. The hypothesis that Cuatro Ciénegas Basin has lower diversity and abundances of aquatic macroinvertebrates than similar aquatic habitats will be considered.

Cichlasoma minckleyi, an endemic cichlid in Cuatro Cienegas, has a trophic polymorphisim. The two common morphs, (detritivore and molluscivore), differ in pharyngeal tooth morphology. Diet studies suggest strong overlap between the morphs. We used stable isotopes to test whether the morphs have different diets. Stable isotopes offer two advantages over diet studies by allowing for large non-destructive samples and providing a temporally integrated assessment of diet. We collected fish from eight habitats and determined their morphology using an otoscope and took a small fin clipping for isotope analysis. Morphs differed in d13C, indicating that they have different food sources, but did not differ in d15N, suggesting that they occupy similar trophic positions. Differences in isotope values among sites did not correlate with the Hemichromis invasion.

The highly endemic aquatic biota of Cuatro Ciénegas was thoroughly surveyed 20-30 years ago, but more recent inventories are lacking. Human-induced habitat alterations have continued since these early surveys, but the area was recently protected by federal decree. Hydrologic alterations (primarily water diversions) and recent introductions of exotic fishes and snails will likely impact the aquatic ecosystems. Knowledge of inter-specific and habitatorganism interactions will be needed to formulate management plans. In summer of 1999 we began a re-survey of the aquatic biota and water chemistry and will compare our preliminary results to historic data from museum collections. Stable isotope studies will help us describe foodweb interactions, and in situ experiments will help us understand interactions between exotic and native organisms.

Cichlasoma minckleyi is a polymorphic cichlid endemic to the Cuatro Cienegas basin in Coahuila Mexico. The two most common morphs (papilliform and molariform) differ in pharyngeal dentition. Understanding how and if morphs segregate among habitat types might prove useful in understanding cichlid diversification, and such information will be necessary for long term management of this species. Fish were captured in Mojarral Oeste (now also called Poza Azul), a clear spring fed pool with at least 5 discrete habitat types, identified by morph, tagged, released, and observed in situ one to two days later. Data were taken on habitat preference and feeding behaviors for each individual. Initial results indicate differences in habitat preferences between morphs. Future observations will encompass other seasons.