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Paris River Fish Monitoring Annual Report smallei fish, making growth seem faster than it really is. In the lab, flannelmouth sucker eggs hatched in 5-7 days at 18.5° C, the larvae were approximately 11 mm TZ. at hatching and grew at a rate of 0.31 mm /day at 20° C (Mike Childs, AGFD, personal communication). However, lab fish may not grow as fast as wild fish due to the ability of wild fish to feed at any time, whereas in the lab, fish can only feed when they are fed. Therefore, I estimated date of hatching based on a growth rate of 0.4 mm /day, which gave an estimated date of hatching between 2 April and 17 May 1998 and an estimated spawning date of 26 March -10 May. This means that flannelmouth ~ suckers probably spawned throughout the period of descending dischazge in the Paris River. It appears from these data that the main spawning period occurred azound 28 April based on the peak length class of 23 mm_ In 1996, the last yeaz in which they were abundant, YOY flannelmouth suckers first appeazed in samples during May (CPUE = 48.7 flannelmouth sucker / 100 m2 seined; Brouder and Hoffnagle 1997a). In 1998, we awaited word of spawning activity before beginning sampling. However, there was no observed spawning aggregation at the mouth of the Paris River nor a run upstream (S. Rogers, AGFD, personal communication). Discharge in the Paris River from 1 January through early June was typical of previous years (Graf et al 1991): spring 1998 air temperature was cool and mean daily discharge ranged from 20 - 35 cfs through early April, then steadily declined to base flow by the end of May (Figure 2). It is unknown why no spawning aggregation was observed this year. In the Little Colorado River, the cool spring and an extended runoff period extended the 1998. spawning period for all native fishes (Hoffnagle 1998). However, flannelmvuth suckers may not require flooding or increasing water • temperature for induction of spawning. Each spring flannelmouth suckers spawn on a gravel bar in the Colorado River approximately 5.4 miles upstream from the Paris (approximately l 0.5 miles below Glen Canyon Dam). Due to-the dam, there is little annual change inflow regime nor a change in water temperature in this area Therefore, it is likely that photoperiod is a strong cue for spawning of flannelmouth suckers. Flannelmouth sucker catch is highest in the spring, with the capture of spawning adults and later YOY (Figure 4). All flannelmouth suckers captured after July 1998 were adults. The loss of the YOY suckers from the Paris River is likely due to monsoon floods which flush young fish into the Colorado River. High catches (4 - SO fish / 100 m2 seined) of YOY flannelmouth • Hoffnagle 1999, Pais River 1998 Affiual Repot Arizona Game & Fish Deparnnent 17