FISHERY BULLETIN: VOL. 76. NO. 2 



Diplodus sargus 



Winter Feeding 



The diet is composed mainly of harpacticoid 

 copepods, amphipods, algae, isopods, polychaetes, 

 and ostracods (Figure 6; Table I, n = 88). 



The diet of the smallest size class (5-15 mm) is 

 composed almost equally of harpacticoid copepods 

 and amphipods, but the percentage consumed of 



the former increases in the next size class whereas 

 that of the latter decreases. The diet remained 

 similar in the following two size classes. In the 35 - 

 to 50-mm size class, the fish fed little on harpac- 

 ticoid copepods, the diet being largely composed of 

 amphipods. The situation was similar in the 

 largest size class, although algae and polychaetes 

 were increasingly taken. 



Summer Feeding 



8 

 & 



100 



80 



60 



40 



20- 



Length (mm) 5 



No. of Fish 9 



Figure 6. — Changes in diet with length of Diplodus sargus, 

 collected between February and July 1975, as shown by the 

 comparative feeding index. Food items included in Others are: 

 brachyurans, crab zoaea, diatoms, echinoderms, hydrozoans, 

 leptostracans, molluscs, mysidaceans, Palaemon pacificus. 

 rhydophytan algae, sand, and unidentifiable animal fragments. 



Although similar to the winter diet, chironomid 

 larvae, diatoms, crab zoaea, and leptostracans are 

 more significant. Cirripede nauplii and an uniden- 

 tified trochophore larva were also commonly 

 taken, and these were not found in winter speci- 

 mens (Figure 7; Table 2, n = 149). 



The diet of the smallest size class (5-15 mm SL) 

 is composed mainly of harpacticoid copepods. The 

 next size class (15-20 mm SL) fed on a similar diet, 

 although the percentage of harpacticoids taken 

 decreased and that of polychaetes and cirripede 

 nauplii increased. These changes were further 

 magnified in the 20- to 25-mm size class. In the 

 next size classes (25-50 mm), there was a change 

 and the green alga, Ulva sp., contributed sig- 

 nificantly to the diet. 



Poor diving conditions in September, October, 

 and December reduced the sample size and only 

 nine fish in the 50- to 165-mm size range were 

 analysed. In general, these fish showed an increas- 

 ing tendency to take more amphipods, and less 



Table 1. — Changes in the percentage composition of the food of Diplodus sargus with length during the period 

 February to July 1975, as assessed by the comparative feeding index (CFI) and occurrence (Occ.) methods. In the 



case of the former, all values exceeding SC/f have been italicized in order to emphasize those food items which 

 contribute maximally to the diet ( — = absent). 



Size classes (mm) 



S^Ts 15-20 20-25 25-35 35-50 50-165 



Taxon CFI Occ. CFI Occ. CFI Occ. CFI Occ. CFI Occ, CFI Occ. 



Chlorophyla ______ 1.3 33.3 1.0 25.0 12.8 41.7 



Rhodophyta — — — — — — — — 0.2 8.3 1.6 16.7 



Chrysophyta — — 02 118 — — — — — — 0.3 2.8 



Polychaefa 2.4 33,3 11.8 76.5 16.7 75.0 3.6 50,0 14 33.3 12,8 47,2 

 Crustacea 



Amphipoda 47.4 77,8 5,8 29,4 5,0 25,0 7.8 66,7 80,7 66,6 58,7 72.2 



Ostracoda 0.5 22.2 4.2 58.8 1.2 75,0 0.2 16.7 0.1 8.3 — — 



Harpacticoid copepoda 45.9 88.9 74 2 82,4 69,3 1000 80.9 66.7 1.3 25,0 0,4 11.1 



Isopoda 1.2 33.3 1,0 35.3 7,4 75,0 5,0 50,0 3,3 50,0 4,2 33.3 



Brachyura (zoaea) — — — — 0,1 12,5 — — — — — — 



Tanaidacea _ _ _ _ _ _ 1 16,7 0,1 8,3 — — 



Macrura ______ 0,1 16.7 0,2 16,7 — — 



Mysidacea _ — — — — — 0,2 16.7 — — 0,1 2,8 



Insecta _ — — — 0,2 12 5 — — — — 1 2 8 



Mollusca ________ 01 83 4,1 22,2 



Echinodermata — — — — — — — — — — 0.1 2.8 



Unidentifiable fragments 2,6 44.4 3.0 52.9 0.1 12.5 8 50.0 12.2 66.7 5.4 52.8 



No of fish examined 9 17 8 6 12 36 

 Average no. of points 



allotted per stomach 18.8 13.4 7.3 20.3 17.2 13.2 



394 



