held back for freshwater rearing. Approximately 

 38^ of the fish in saltwater were found to have the 

 gallbladder condition by mid-October. The condi- 

 tion did not develop in those remaining in fresh- 

 water. 



In all cases observed thus far, affected fish were 

 young ( <2 yr) salmon that had been reared exclu- 

 sively on commercially prepared pellets. With the 

 exception of the occurrence in Oregon, all cases of 

 the abnormality have occurred in saltwater net 

 pens. 



With dietary adjustments the condition is ap- 

 parently reversible. In an unrelated nutrition 

 study, 757c of the subsamples of one lot of 1,800 

 coho salmon that had been fed a ration of OMP for 

 several months had impacted gallbladders. These 

 test fish were divided into two lots. One group 

 (1,400) was fed a laboratory prepared moist pellet 

 diet and the remaining fish (400) were continued 

 on the commercial OMP diet. After 4 mo, subsam- 

 ples indicated that incidence of abnormal 

 gallbladders in fish on the laboratory diet had 

 been reduced to 5%. Incidence of the condition in 

 the test group maintained on the OMP diet re- 

 mained at 759c. 



Discussion 



I have found no published information relative 

 to gallbladder abnormalities in fishes. The 

 pathological features described for this condition 

 do not resemble any infectious disease currently 

 described for fishes and are more suggestive of a 

 toxic or nutritional disorder. 



The biliary system is an integral part of the 

 digestive apparatus, playing an important role in 

 lipid digestion. It also provides a mechanism for 

 recycling certain metabolic byproducts of hepatic 

 origin through the digestive system. Many of 

 these metabolic byproducts are excretory wastes 

 while others can be salvaged for reuse by rediges- 

 tion. Studies as yet do not prove a major detrimen- 

 tal effect of this condition on the fish. Knowing the 

 importance of the biliary system, however, it is 

 inconceivable that it does not have an adverse 

 effect on the animals' nutritional status, particu- 

 larly in relation to systems dependent upon 

 adequate and diverse lipid supply. 



Acknowledgments 



I thank Kenneth Pierce; graduate student, Uni- 

 versity of Washington, Seattle; for preparing the 



gallbladder specimens for histological examina- 

 tion. 



Lee W. Harrell 



Northwest and Alaska Fisheries Center 

 National Marine Fisheries Service, NOAA 

 2725 Montlake Boulevard East 

 Seattle. WA 98112 



TIMING OF THE SURFACE-TOBENTHIC 



MIGRATION IN JUVENILE ROCKFISH, 



SEBASTES DIPLOPROA, OFF 



SOUTHERN CALIFORNIA 



Species of the genus Sebastes lead a pelagic exis- 

 tence as larvae, transforming to pelagic pre- 

 juveniles and finally benthic juvenile stages at 

 varying sizes (Moser 1967, 1972). Pelagic pre- 

 juveniles of some species often congregate under 

 drifting objects (Hitz 1961); off the coast of south- 

 ern California, Sebastes diploproa (Gilbert 1890) 

 is the dominant rockfish species found under drift- 

 ing kelp ( Mitchell and Hunter 1 970). Adults of this 

 species inhabit a bathymetric range of 91-578 m 

 and a latitudinal range from Alaska to Baja 

 California (Hart 1973). Little is known about the 

 movement of this rockfish from surface to benthic 

 waters. This paper provides information on the 

 disappearance from surface waters and the ap- 

 pearance in the benthic habitat based on seasonal 

 size distribution from the two habitats. 



Materials and Methods 



Surface prejuveniles were collected by dip net 

 off San Diego, Calif, (lat. 32°52'N, long. 

 117°30'W), from beneath drifting kelp (primarily 

 Macrocystis pyrifera) during 1975 and 1976. 

 Benthic juveniles were sampled in standard 

 10-min bottom trawls with a 7.6-m (25-ft) otter 

 trawl (12.7-mm stretch mesh cod end liner) in 

 1972 through 1976. Most trawls were made in and 

 around the Los Angeles Bight from Point Dume 

 (lat. 34WN, long. 118°48'W) to Dana Point (lat. 

 33°28 'N, long. 117°43'W) at depths from 92 to 183 

 m, although small S. diploproa were captured as 

 shallow as 46 m. This does not encompass the 

 entire adult bathymetric range, but younger 

 stages of Sebastes generally tend to occupy shal- 

 lower parts of the adult range (Kelly and Barker 

 1961; Moser 1967, 1972; Westrheim 1970). Only 



887 



