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opment. Larvae collected in February 1983 tended to be developmentally older than those in January. Laboratory studies Embryos successfully hatched in the laboratory at 10-2<r C but there were no viable embryos hatched at goC (Table 2). Hatching success ranged from 22 to 57% at ur C. 32 to 65% at 15" C, and 34 to 65% at 20" C. Optimal hatching temperatures appear to be from 12-200 C where hatching success was simi- lar within experiments. Although success was con- siderably lower at 1000C than at 15 or 2O"C in two experiments. it was remarkably high in the first experiment (57%). ll1C highc!\t mortality during incubation w~ at HrC occurring prior to the morula stages. Almost 30% greater mortality occurred at J(rc in experi- ment D during these pre-morula stages than at either ISor 2<r C. The effect of vacillating temper- atures varying between 8.5 and 1l.50C in experi- mental chambers is unknown. Dcvelopment rate was positively related to tem- perature (Ta,ble 3). Hatching time for 50% of the eggs was 420.:556 h at 10" C. 256-298 h at 15" C. and 158-168h at 20"C. Swim-up for 50% of the larvae took ~ times longer at 1000C than at 20"C. Devel- opment rate for larvae through yolk depiction was 259 also positively related to temperature although ex- periments were usually terminated prior to full yolk depletion for all larvae at IO"C. Oxygen con- sumption increased with increased temperatures at all developmental stages (Fig. I). Oxygen con- sumption also increased with development at each temperature. The largest increase in oxygen con- sumption was associated with the swim-up devel- opment stages. Likewise, variability was also high- est among replicates at these stages. possibly due to the different physiological abilities to swim. Discussion Comparison oj hatching success OUr laboratory data indicate that spawning by ra- zOrback suckers is successful at 100ZZOC. These temperatures correspond to those occurring in Lake Mohave during their 7-month spawning sea- son. November through May. Larvae collected from Lake Mohave at 10-150Cconfirmed labora- tory resulls thaI lower temperatures did nol pre- clude successful spawning. Hatching success in the laboratory was similar between 12 and 2O"C, but reduced at 1000C in one experiment. Hatching 8Ucces."i at ur C was never less than 50% of the warmer incubation temper- TRM('.t. Innucncc of temperature on hatching and dcvctormcntal ratC5. ValUC5 ate houl'5 5ince insemination when SO"4 or the individuals per II8mplc: attained a particular developmc:ntal tnte",al. Range of development times expressed as S% and 9S% individuals att:linin~ a particular developncntal interval are in parenthe~. EXf'Criment Temp. C- I-Iateb ^ H c III 10 15 2f1 II 12 15 2f1 II III 15 2tl 55(, (5:U~24) 212 (242-JJO) HlR (I 49-IIU) 4:!O (JI2-~I4) 449 (2.<iJ-.624) 2.<i6(1%-312) 15X(II~2Ih) 444 (371}-.542) 19X (241-355) 1(,2 (150-173) o Swim-or YoIk-dcplction (,12 (5CJI-R<i5) IlM (648-1032) 40R (J60-.504) 2XR (2.<i9-334) R1CJ ((I.~99CJ) 1(lJ2 (984-.) 552 (5~4) 40R (360-432) lWll (744-0) . 5(1(, (4fl2-530) 2M (264-J04) (,JO (552-720) 44ft (408-4RO) . ElI:f'Crimenl was terminated prior 1095% or the individuals reaching thC5e dcvelopmcntallilages.