TABLE 1. — Mean back-calculated standard length (mm) and 959 confidence intervals at 

 successive annuli for splittail taken in the Suisun Marsh, Calif., 1979-80. 



same maximum size encountered by Caywood 

 (1974). No sex-related differences in growth were 

 detected (f-test, a = 0.05). 



Monthly mean condition factors of mature fish 

 varied little throughout the year (Table 2). Mean con- 

 dition factors were significantly higher in females 

 during the months preceding spawning (f-tests, a = 

 0.05); sex-related differences were not significant in 

 other months. The condition factors of immature fish 

 generally were not significantly different from those 

 of mature fish (<Ntests, a = 0.05). Between-year dif- 

 ferences in mean condition factors were not signifi- 

 cant in mature fish. However, immature fish of the 

 1978 year class (immediately postdrought) had mean 

 condition factors significantly higher than those of 



the 1979 year class in March (t 

 April (t = 1.73 > t 0JNS ). 



4.81 > W and 



Table 2— Mean monthly condition 

 factors of splittail from Suisun Marsh, 

 Calif., 1979-80. No data are available 

 for December. 



Reproductive Biology 



Sacramento splittail were mature by their second 

 winter, at minimum lengths of 180-200 mm; both 

 males and females matured at the same age. 

 Caywood (1974), however, noted that a small percent- 

 age of the males became sexually mature at the end of 

 their first year and a small percentage of the females 

 did not become mature until their third year. Gonadal 



growth began to increase in the autumn at about the 

 same time somatic growth declined. Ovaries in- 

 creased in size until April when they account for 18"% 

 of the body weight; testes reached their greatest size 

 in March, April, and May, but never accounted for 

 more than 27c of body weight. Splittail spawned in 

 late April or early May in the marsh. Caywood (1974) 

 found that spawning in the upper Delta occurred be- 

 tween early March and mid-May (in 1973 and 1974). 

 Young-of-the-year fish appeared in our collections in 

 late May or early June at 22-40 mm SL; at this size 

 they had absorbed the yolk sac and were free 

 swimming. 



The fecundity (F) of 20 fish > 1 75 mm SL collected 

 from January through March ranged from 17,500 to 

 266,000 ova. Mean number of ova per gram body 

 weight (Wt) was 408; in this sample the relationship 

 between number of ova and body weight was F = 457 

 (Wt) - 91 (log- log transformation r = 0.546; F= 7.64 > 

 F u8 at P — 0.05). They averaged 600 ova/mm SL. 

 The relationship between fecundity and SL was F = 

 0.01 (SL) 2 - 92 (log-log transformation r = 0.536; F = 

 7.25 > F u8 at P — 0.05). Fecundity increases with 

 length and weight; both adequately predict 

 fecundity. 



The onset of spawning appears to be associated 

 with increasing water temperatures and increasing 

 day length; during the spawning period there were no 

 changes in turbidity or salinity. The success of the 

 spawn was correlated with river outflow (Table 3). 

 Caywood (1974) captured ripe splittail in the upper 

 end of a freshwater slough, in association with recent- 

 ly flooded vegetation. It is possible that splittail 

 spawn on vegetation. 



Year Class Strength 



The percent of each year class in the catch varied 

 (Fig. 3). The 1978 year class was extremely strong 

 and dominant through the 1980 summer. The 1979 

 year class was never strong and never clearly 

 dominated a monthly sample. Instead it remained 



650 



