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L in the Yampa River ('-50 mg/1 CaCO ), metals could be toxic to Colorado squawfish, particularly mewly hatc~ed larvae. Standards for this tribu- tary could be drawn in part from this report's toxicity data. Water- born heavy metals do not appear to be affecting the population at this time . Pesticides are not affected by the dissolved solids or hardness and, therefore, have importance throughout the Colordo River system. Water-born pesticides do not appear to be near toxic concentrations and are only reported in trace amounts by USGS. While the direct effects of the chemicals tested may not threaten the squawfish now or in the future, most of these chemicals are also carried via the food chain and have been shown to accumulate in fish tissue to levels thousands of times higher than those found in water or sediment. A11 the heavy metals and pesticides tested here are found to some degree in the tissue of Upper Colorado River fishes but are still at relatively low concentrations (National Pesticides Monitoring Program data). An additional hazard to eggs and larvae is suffocation. While adult fish may succeed in spawning, the squawfish like most cyprinids, is a broadcast spawner and neither makes nor guards a nest. Once the eggs are deposited, if they become covered with silt or debris, lack of water exchange will cause their death through lack of oxygen or build-up of metabolites around and within the egg. Also, larvae may be trapped or prevented from hatching. Food An abundance of small fishes, mostly introduced species like the red shiner, provides an ample food supply for the predacious Colorado squawfish. Stomachs of YOY (22-59 mm) from the Green River contained about 85% fish remains identif ied as red shiners ( ~~'"'~^~ K ~9$i). Even five-year old sub-adult squawf ish seem to be capable of finding an ample food supply. Of 1500 stocked near Moab, Utah, 13 were recaptured in good condition up to a year Iater. Most had increased in length and weight. In fact, one grew 11 f m 270 to 381 and 420 g TL from 140 g to 580 g in 13 months ( ). From information L-- accumulated under this study, we do not believe that food is a limiting factor for any of the life stages of Colorado squawfish. Health Our field sampling over the past 2~ years shows that sub-adult and adult Colorado squawfish are relatively low in number and do not attain the size they once did. However, the majority of sub-adults and adults sampled were healthy specimens capable of migrations of hundreds of miles and of enduring the rigors of spawning. Disease examinations of 11 adults taken by our field crews revealed a variety of bacteria and parasites particularly among those fish under stress-from handling and captivity (Appendix . Learnaea, an anchor worm easily seen with the `' naked eye, was very common but does not appear to cause mortality among sub-adults and adults. In the wild, these diseases may occasionally affect individual fish.