Cottus Life History in Delaware 



89 



Table 6. Combined monthly averages of coefficient of condition (K) for male 

 and female Cottus bairdi from Butler Mill Branch, Sussex County, 

 Delaware, 1973-1980. Male N = 145, female N = 278. 



Month 





Male 



Gonads 



Gonads 



in situ 



excised 



2.06 



2.06 



2.10 



2.08 



2.88 



2.84 



3.07 



3.07 



2.88 



2.88 



2.53 



2.70 



3.33 



3.33 



2.36 



2.26 



2.19 



2.17 



2.34 



2.32 



Female 

 Gonads Gonads 



in situ excised 



Jan. 



Feb. 



Mar. 



May 



Jun. 



Jul. 



Aug. 



Sep. 



Oct. 



Nov. 



2.06 



1.93 



2.44 



1.96 



2.58 



2.12 



2.63 



2.62 



2.67 



2.65 



2.27 



2.26 



2.68 



2.66 



2.14 



2.06 



2.20 



2.17 



2.39 



2.34 



Food Habits 



Based on stomach contents of 539 fish ( 1 2-64 mm SL), food is prim- 

 arily larval trichopterans (in 55.7% of stomachs) and dipterans (42.3%), 

 and plecopteran nymphs (19.7%); less important are crustaceans (9.2%), 

 ephemeropteran nymphs (8.0%), and coleopteran larvae (2.4%) (Table 7). 

 Nineteen taxa were identified. One hundred and twenty-eight (23.7%) 

 stomachs were empty. Franz and Lee (1976) found 5 taxa in 10 speci- 

 mens. Ricker (1934), Koster (1936, 1937), Dineen (1951), Bailey (1952), 

 and Daiber (1956) also found that the primary food was benthic insect 

 larvae. 



Seasonal variation in diet is evident (Table 7). Trichopterans, mainly 

 Hydropsychidae, were eaten in all months except February, and were 

 dominant in March, July, August, and September. Dipterans, primarily 

 Chironomidae, were the most common food in January, June, October, 

 and November. Plecopterans were common from January through May. 



Prey taxa differed only slightly by fish size group (Table 8). Chiro- 

 nomids were relatively more important to sculpins smaller than 19 mm 

 SL than to longer fish. Larger specimens (>49 mm SL) ate fewer chiro- 

 nomids but more larger simulids. A 43 mm SL sculpin contained one 25 

 mm SL Etheostoma olmstedi, and a 53 mm SL specimen had eaten an 

 egg of Lampetra aepyptera. 



