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198 THANS, AMElt FISK SOC, 1969, NO, 2 TAllu: 3,-M""1I ClIlclll,ued totllllenglh.s and ann/Ull increments, Colorado sqllawfish, Green River, 1964-1966 ( Mean NUlllber lotal Mean calculated length (mill) at annulus A!(c of )cn~lh group fish (mm) 2 3 4 5 6 7 8 9 10 11 I 51 74 43 11 38 107 40 83 III 16 168 39 82 136 IV 16 229 43 92 148 205 V 16 329 47 78 164 231 298 VI 16 400 50 110 181 259 325 376 VII 9 465 47 100 169 252 321 386 432 VlII 7 50S 47 103 176 250 335 402 461 492 IX , 537 51 lO8 165 226 305 382 445 487 523 X 5 576 54 118 189 273 349 429 487 520 550 568 XI 1 610 48 99 185 269 372 464 507 532 5fi.t 583 600 --------------------------------------------------------------------------------------- Grand nvera~e length 44 95 162 238 320 391 454 499 536 570 600 Number of fish 182 131 93 77 61 45 29 20 13 6 1 Av('ragc Icn~lh increment 44 51 64 71 73 63 55 3.5 3,1 18 17 A\'t'nl~(' l'nklllnll'd \H.iC"hl (J.:)1 I 0 30 10.] 200 47H 7,f)7 ](HO 1220 J.57.r; 18;;0 1 Calculated from length-weight regression. 1('diuIIS nllllle shorlly arrer high waters hegall 10 recede in early June, and oecame scarce as summer progresscd. This apparent sea. sonal reduction in abundance of young fish was probably due (in addition to mortality) to decreasing susceptibility to seining as a result of their increased size, Fish in all Ihree age-groups (O-IIl grew throughout the season, and the length.fre- quency distributions of these groups c1us- lered about their respective means with no significant overla!l (Figure 4). Ages assigned by the length-frequency analyses were in gen- eral agreement wilh the ages and lenglhs calculated from the scale analyses, Mean length of young-of-the-year fish in latc Au- gust of 1966 was 24 mm, while in 1964 and ] 965, mean lengths at this time were 18 and ]5 mill, respectively, This lar;.>:cr size was rdated 10 an carlier spawnin;.>: s('a~on in 1966, Taft and Murphy (1950) reported that the oldest Sacramento squawfish (P, grandis) T.~IILE 4.-Pcrcelllllt:" devit/lioll from mran allllllal iIlC''''II'''1I1 of t:rOWIh. in lolt// [,'Ilglh, C%rt/do squllw/ish t/lld C%rlUlo chub (rout/dlt/il t/nd lJOn)', It/i/ forms), Gr,'ell /{ilw, 1958-1965 Percentage deviation from mean annllalillcrcmcnt Year Squawfi~h nOlln()lail lIonylail 1951l +19.0 1959 +12.1, +2,4 +2.7 1!l60 +15,7 +4.0 +5.9 1961 + 8.7 +5.8 +0.5 1962 - 2.3 +9.4 +7.0 1963 -11.5 +2.3 -6.1 1964 -15.2 -10.6 -2.2 1965 -27.1 -13.3 -7.6 taken in their stndy from the Sacramentu River was 9 years old. The mean calculated standard length at the first annulus was 60 mm and the largest annual growth incre- ment was 80 mm during the second year of life. The largest northern squawfish (P. ore- gonensis) taken in northem Idaho IlY Jepp- son and Platts (1959) was a 13-year-old female which had a total length of 673 mm and a weight of 4036 gms. Jeppson and Platts also reported that this species grew most rapidly in the second and third years uf life, and that the males grew slower than females. Casey (1962) found that the northern squaw- fish in Cascade Reservoir, Idaho, attained its most rapid growth in its third year, and that growth declined after the sixth year. The oldest fish was 11 years old and 476 nnll standard Icnglh, hut squawfish over 7 years old were rare in Cascade Reservoir. CoIorwlo Chub Age and growth determinations of Colo- rado chubs were based upon scale samples from 333 specimens, including 49 identified as roundtails and 67 as bony tails. Annuli were counted and scale lengths were mea- sured in the anterior field, The largest and oldest roundtail in this study was a 7-year- old female 366 mm long weighing 393 gms. The oldest and largest bony tail was 7 years old, 3gB mm long, 422 gillS, and of unde- termined sex, The roundtail amI bony tail forms of the