FISHERY BULLETIN: VOL. 79, NO. 1 



We consider 27 of the most abundant fish species 

 in the nearshore waters at Santa Catalina Island, 

 describing what each does during twilight and at 

 night, and noting the wavelengths of light to 

 which the scotopic system of each is most sensitive 

 (A^^^). In examining the retinae from the fishes, 

 we noted whether the visual pigments were 

 homogeneous. Significantly, there were no sec- 

 ondary pigments in 12 species and only a trace in 

 5. Secondary pigments, which presumably are 

 cone pigments (Munz and McFarland 1975), were 

 present in 10 species and abundant in only 3. The 

 data are given below, grouped according to that 

 segment of the diel cycle when the species obtains 

 most of its food. It is important that we observed 

 only slight variation in the A^iax of any one species. 



Fishes That Feed Primarily by Day 



Some of the fishes that feed primarily by day are 

 known to be inactive at night, but evidence of 

 nocturnal inactivity remains lacking for others, 

 and still others are known to feed routinely after 

 dark. The predominantly diurnal Californian 

 fishes considered in this paper, along with certain 

 of their visual characteristics, are listed in Table 1. 

 The following accounts of diel activities emphasize 

 crepuscular and nocturnal habits. 



Table L — Some southern Californian marine fishes that feed 

 primarily by day, with the spectral absorbance maximum (^niax^ 

 of pigments extracted from their retinae. 



'Other than the primary pigment: = none; T = trace; + = <10%; ++ = 

 >10%. 



^Visual pigments for these species were also studied by Munz (1957, 1958b, 

 c, 1964). He reported similar A^iax values for all but £ jacksoni, which he listed 

 (Munz 1958b) as 506 nm. The difference can be attributed to varying amounts 

 of secondary pigments in his extracts, which can bias the \max estimates if not 

 taken into account 



^Visual pigments in these species are porphyropsins, which are based on the 

 aldehyde of Vitamin A2. Pigments in all other species are rhodopsins. which 

 are based on the aldehyde of Vitamin At. 



^Halichoeres semicinctus and O. californica excluded owing to basic 

 differences in their pigments (see footnote 3, above). 



Atherinidae: Atherinops affinis 



The topsmelt aggregates by day in the surface 

 waters close to kelp forests, but at night most 

 larger individuals move away from the kelp and 

 disperse close beneath the water's surface over 

 adjacent deeper water. At first we suspected these 

 larger individuals might feed after dark. Their 

 movements are similar to those of tropical Pacific 

 atherinids of the genus Pranesus, which are 

 known to be nocturnal feeders (Hobson and Chess 

 1973; Hobson 1974; Major 1977), and nocturnal 

 habits are widespread in other planktivorous 

 atherinids, including A //anei^a harringtonensis in 

 the tropical Atlantic Ocean (Starck and Davis 

 1966). Furthermore, we have often seen 

 Atherinops affinis feed at night next to illumi- 

 nated piers, although we consider this an artificial 

 situation. 



Despite the evidence of nocturnal feeding in 

 other atherinids, however, our suspicions concern- 

 ing A. affinis were contradicted by examination of 

 gut contents. Of 22 individuals (129-219 mm SL, x 



= 168.8) collected at davni as they reassembled in 

 schools along the outer edge of kelp forests, 19 

 were empty, 2 contained just a few fish scales, and 1 

 contained calanoids and cyphonautes larvae that 

 appeared recently ingested — probably since sun- 

 rise that morning. At least some of the smaller A. 

 affinis remain close to the kelp at night, but there 

 is little evidence that they feed during that period. 

 Of 10 (82-160 mm SL, jc = 102.4) collected close to 

 kelp during the hour before dawn, 9 were empty. 

 The one with food, however, contained three gam- 

 marids and one isopod that obviously had been 

 taken at night. In contrast, there is ample evi- 

 dence that A. affinis feeds intensively during the 

 day. We routinely observed this species feeding in 

 the surface waters during all daylight hours, and 

 only 1 of 10 (126-190 mm SL, 3c = 158.6) collected 

 from a large aggregation during midafternoon 

 lacked food in its gut; the other 9 contained x = 

 1,325 prey items, mostly cladocerans and 

 copepods. 



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