7203 - Laserfiche WebLink

Home Browse Search

1 1 t t 1 t 1 1 of squawfish to cannibalism. No squawfish were found in the stomachs of the 290 squawfish we examined. Disease. Asian tapeworm (Bothriocephalus acheilognathi), an exotic ces- tode found infecting squawfish in West and Humphrey ponds, was not detect- ed in Fish Chalet Pond, nor was any other obvious disease noted. Water Quality. Dissolved oxygen became low in Fish Chalet Pond during July and August 1987, but apparently only in the lower depths (Fig 4). Our data indicate that the upper 1.0 m of water always had at least 10 mg/L. However, night-time dissolved oxygen levels were not measured and thus could have become limiting at some time without our detecting it. There was no evidence of winter kill at Fish Chalet Pond. No dead fish were seen floating or washed up on the shore in early spring; however, clarity of water was so low that dead fish that may have been on the bottom would not have been observed. After finding dead squawfish at nearby West Pond after ice-out in early 1988, we collected water samples from there and from Fish Chalet ponds to determine concentrations of hydrogen sulfide (H2S), a potentially toxic by-product of decomposition. Four samples were collected from Fish Chalet Pond on 15 March; samples were from the bottom and mid-depth at two locations. Two samples con- tained high levels of H2S: a mid-depth sample from the north end of the pond had 0.047 mg/L and a bottom sample from the south end had 0.101 mg/L. Smith et al. (1976) experimentally tested the toxicity of H2S to bluegill and found a 96-hr LC50 to be 0.04778 mg/L for juveniles and 0.0448 mg/L for adults. Thus, if toxicity of H2S for Colorado squawfish is similar to that for bluegill, H2S reached lethal levels in at least some portions of 18