LOVE and WESTPHAL: GROWTH AND FOOD HABITS OF OLIVE ROCKFISH 



fertilized stage, the eggs are clear and turn gray 

 as larvae develop in the ripe ovaries. 



Mature males undergo a simpler cycle. Resting 

 stage testes are small and brown, becoming larger 

 and whitish brown as they develop. Fully devel- 

 oped testes are large, white, and delicate. 



With this information, it was possible to deter- 

 mine when fish reproduced and when insemina- 

 tion occurred. Stages of gonad maturation (condi- 

 tion) in 1,056 adult olive rockfish, taken during 

 1972-77, were determined using the criteria of 

 Westrheim (1975). A gonadosomatic index (gonad 

 weight) /(total body weight) x 100 was computed 

 to quantify changes in gonad size with season. 



For fecundity estimates the ovaries of 83 ma- 

 ture fish captured in October and November were 

 placed in modified Gilson's solution (100 ml 60% 

 isopropanol, 880 ml freshwater, 15 ml 80% nitric 

 acid, 18 ml glacial acetic acid, and 20 g mercuric 

 chloride — Bagenal and Braum 1971) to harden 

 the eggs and were periodically shaken to loosen 

 them from ovarian tissue. Eggs were kept in the 

 solution for about 2 mo, after which the fluid was 

 poured off and replaced with water. Before eggs 

 were counted, the ovaries were further broken up 

 and repeatedly washed with water to remove 

 remaining connective tissue. The eggs were placed 

 in a larger beaker and water was then added until 

 2,000 ml of eggs and water had been obtained. The 

 mixture was stirred magnetically until the eggs 

 were homogeneously distributed throughout the 

 water column, and a 5 ml subsample was drawn 

 with a pipette. Three subsamples were taken. 



Eggs in each subsample were counted, using a 

 dissecting microscope, and the mean number per 

 milliliter was calculated for the three subsamples. 

 Fecundity was then estimated by back calculation. 



Food Habits 



Specimens were collected nearly every month 

 between May 1975 and April 1977 by hook and line 

 and pele spear (in about equal proportions), im- 

 mediately placed on ice aboard the diving vessel, 

 and frozen soon after for later examination ashore. 

 A total of 591 specimens were collected, of which 

 374 (63.3%) had some food in their stomachs. We 

 took precautions that only artificial lures were 

 used and chumming or other disturbances were 

 avoided, so that sampling method did not bias the 

 stomach content composition. 



Stomach contents were sorted taxonomically 

 into 17 food items and the volume of each category 



was measured by liquid displacement. Food items 

 were also grouped into three prey types (substrate 

 oriented, nekton, and plankton) based on prey 

 behavior and habitat. Nektonic prey included all 

 nonlarval fish and squid. Substrate-oriented prey 

 included all prey (except fish) that live on or about 

 reef and plant surfaces; these may be motile, such 

 as octopus, or attached, like algae. 



To examine seasonal variation in diet within 

 each size class of olive rockfish (except 10.1-20.0 

 cm which had too few specimens), food data was 

 pooled by seasonal periods roughly corresponding 

 to "upwelling" (March- August) and "oceanic" 

 (September- February) oceanographic regimes off 

 the Avila area (Bakun 1973). 



RESULTS AND DISCUSSION 



Age and Growth 



There was no published work in aging olive 

 rockfish (with the exception of a few fish men- 

 tioned in Burge and Schultz^), and the use of the 

 otoliths in age studies had not been validated. To 

 determine if the opaque and translucent zones 

 were annular, we observed the development of the 

 opaque zone on the edge of otoliths of fish from 

 Avila, taken during a 5-yr period. The occurrence 

 of a particular zone among most or all individuals 

 during one part of the year would indicate that the 

 zones were suitable for age determination (Wil- 

 liams and Bedford 1974; Dark 1975). Because the 

 opaque zones become narrow and difficult to 

 distinguish in older fish and the timing of zone 

 deposition may be influenced by the species' age or 

 state of maturity (Williams and Bedford 1974; 

 Dark 1975), we limited sampling for otolith valid- 

 ity to 1- to 3-yr-old (immature) olive rockfish. 



Data indicated that the opaque zone deposition 

 was seasonal (Figure 2). The percentage of otoliths 

 with opaque edges was low during fall and winter, 

 but rose abruptly during late spring and peaked in 

 summer months. Hence, the production of opaque 

 zones coincides with the upwelling period along 

 central California (Bakun 1973) and probably 

 reflects increased feeding and growth. The per- 

 centage of opaque zones during the early spring 

 may be underestimated as the newly deposited 

 opaque material is quite thin. On the other hand. 



•'Burge,R.T.,andS. A.Schultz. 1973. The marine environ- 

 ment in the vicinity of Diablo Cove with special reference to 

 abalones and bony fishes. Calif. Dep. Fish Game, Mar. Res. 

 Tech. Rep. 19, 433 p. 



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