8147

• UCREFRP Catalog Number: 8147
• Author: Scoppettone, G. G.
• Title: Interactions Between Native and Nonnative Fishes of the Upper Muddy River, Nevada.
• USFW Year: 1993.
• USFW - Doc Type: \
• Copyright Material: YES

NATIVE AND NONNATIVE STREAM FISH INTERACTIONS 605
TABLE 4. -Food items consumed by cohabiting fish species in three habitat types in the Warm Springs.area. Data
are percentages of stomach content volume and (in parentheses) percent frequencies of occurrence. Ten adults of
each species were taken at each site (western mosquitofish were present only at one site).
Moapa White Western
Moapa dace River springfish Shortfin molly mosquito fish
Food item (N = 30) (N = 30) (N = 30) (N= 10)
Gastropoda
Trydnia clathrata I (I) 2 (5) 11(4)
Flurninicola alvinalis 2 (5) 2 (I)
Melanoides tuberculaturn 2 (I)
Oligochaeta 27 (5)
Ostracoda (I)
Amphipoda
H ya//ela azteca 2 (2) 6(9) I (1)
Arachnida
Hydracarina (I)
Ephemeroptera
Tricorythodes sp. (I)
Odonata
Argia sp. 2 (2)
Hemiptera
Pelocoris shoshone 5 (I) (I) 5 (I)
Homoptera
Aphiidae 9 (I)
T richoptera
Pupae 4 (4)
Dolophilodes sp. 5 (2)
Srnicridea sp. ' 6 (5) 4 (2)
Nectopsyche sp. 5 (2) 1(2)
Lepidoptera
Paragyractis sp. 5 (2) I (I)
Coleoptera
Elmidae (larvae) (I)
Stenelrnis calida I (I)
Dytiscidae 9 (I)
Diptera
Chironomidae 5 (I) 9 (9) 2 (I) I (I)
Muscidae 2 (I)
Hymenoptera I (I)
Atherinifonnes
Poecilia mexicana 10 (I)
Vascular plants 3 (2) 1(3)
Filamentous algae 19 (II) 36 (21) 45 (25) 33 (8)
Detritus 3 (3) 28 (18) 48 (26) 33 (10)

springfish took larvae in only 10 of 12 aquaria,
consuming less than 15% of the total larvae avail-
able. They did, however, consume all five Artemia
in each aquarium within the first 2 h. Predation
by shortfin mollies was greater; they consumed
larvae in 12 of 12 aquaria, eating 65% of the larvae
available. Western mosquito fish consumed larvae
in 11 of 12 aquaria and took 60% of the larvae.
Except for one western mosquito fish that ate noth-
ing, the nonnative fishes consumed all Artemia
within 2 h.

Discussion

The hypothesis that interspecific competition
between adults for microhabitat caused the de-

cline of Moapa dace was not supported; there was
virtually no overlap in microhabitat use, and ex-
amination of habitats with various combinations
of species showed no clear indication of a shift in
spatial habitat use caused by competition with
shortfin molly and western mosquitofish. How-
ever, interspecific competition for space and food
cannot be ruled out for larvae and juveniles, be-
cause there was at least moderate interspecific mi-
crohabitat overlap. Ontogenetic shifts in food items
consumed by each of the four species greatly add
to the complexity of determining the potential for
competition, but to document such feeding shifts
would require sacrifice of a larger sample of the
endangered Moapa dace. Thus, the scope of this