pie of splittail taken in a flooded pond, however, the 

 main food was earthworms {Lumbricus sp.). The 

 types of prey consumed indicate that splittail are bot- 

 tom feeders. Feeding activity, inferred from fullness 

 indices, was greatest during morning and early after- 

 noon. The mean fullness index for fishes collected 

 from 0600 to 1400 was 5.4, the mean index for fishes 

 collected at 1800 and 2200 was 2.3. There was a 

 seasonal difference in fullness indices of fishes 

 collected midday (Kruskal-Wallis x 2 = 28.9 >X 2 o.9<))- 

 The greatest mean index (2.8) was calculated from 

 fishes collected during the summer. Mean autumn, 

 winter, and spring indices ranged from 1.3 to 1.8. 



sources of food. The periodic fall in water level 

 simultaneously concentrates prey in the remaining 

 shallow water and excludes large predatory fishes. 

 Avian and mammalian predators are thwarted in all 

 but the most shallow water by its turbidity. 



Tolerance to relatively high salinities is unusual in 

 cyprinids although tolerances similar to that of split- 

 tail have been recorded for carp, Cyprius carpio, and 

 peamouth, Mylocheilus caurinus (Scott and Cross- 

 man 1973). It is likely that salinity tolerance in split- 

 tail increases somewhat with size, as many large (200 

 mm SL +) adults were collected from the more saline 

 areas (>8%o). 



Discussion 



Sacramento splittail is a major component of the 

 Sacramento-San Joaquin estuary fish association. 

 Although abundant within its range, Sacramento 

 splittail is now confined to the lower Delta and the 

 main channel of the Sacramento River, a fraction of 

 its former distribution (Moyle 1980). Population size 

 fluctuates drastically from year to year and year class 

 strength varies annually. 



Within the Suisun Marsh, Sacramento splittail is 

 dominant, by number, in the small cul-de-sac sloughs 

 where it is associated with other native fishes (Moyle 

 et al. 1982b). It is a benthic feeder with a limited 

 range of prey types. Neomysis mercedis, the primary, 

 nondetritus/substrate component of its diet, is abun- 

 dant throughout the marsh and serves as a major food 

 source of most other fishes in the marsh as well 

 (Moyle and Daniels unpubl. data). 



Sacramento splittail grows to moderate size, lives a 

 relatively long life, and produces a large number of 

 eggs per year. This is typical of native California cyp- 

 rinids, particularly those found in the larger rivers 

 and lakes (Moyle et al. 1982b). Such a pattern allows 

 this annual spawner to fail to reproduce during en- 

 vironmentally unfavorable years. Unfavorable con- 

 ditions, which, in the case of splittail, may include 

 high salinities, low water levels, and/or high tem- 

 peratures, are (or were) periodic and predictable. 

 Particularly dry years occurred in 1972, 1976, and 

 1977. During these years splittail either failed to 

 spawn or the spawn failed to develop; however, 

 adults were present in the sloughs. A similar 

 relationship between year class strength and out- 

 flows has been demonstrated for striped bass for the 

 years 1959-76, although since then the relationship 

 has not been as strong (Stevens 1980). 



The small shallow sloughs lined with emergent 

 vegetation inhabited by splittail offer protection 

 from larger piscivorous fish and provide abundant 



Acknowledgments 



In a project that lasts many years and includes over 

 100 sampling days, many people are responsible for 

 its success. We thank all the individuals, mostly 

 volunteers, who helped in the field. We are par- 

 ticularly grateful to D. M. Baltz, B. L. Herbold, and L. 

 M. Brown for continued assistance in the field and 

 laboratory and for reviewing the manuscript. We also 

 thank R. L. Brown, who was instrumental in securing 

 the resources necessary to complete this project, and 

 D. Kohlhorst of CDFG, who allowed us to examine and 

 report unpublished information collected over a 7-yr 

 period. This work was supported by grants from the 

 California Department of Water Resources. 



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1974. Contributions to the life history of the splittail 

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1982. Growth of adult striped bass in the Sacramento-San 

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653 



