Morphological Shifts In Digestive Tract And Diet Composition Of Larvae And Juveniles Of Flounder Catathyridium Jenynsii From Itaipu Reservoir, Parana River, Brazil

The objective of this study was to characterize the diet and digestive tract morphology of flounder, Catathyridium jenynsii (Gunther, 1862) (Achiridae), in its early stages of life. For analysis of the digestive tract, we used a specimen of each larval stage, pre-flexion to post-flexion, and juvenile. A total of 256 larvae and 16 juveniles, belonging to five classes of standard length was analyzed for diet. Data were collected in the Itaipu Reservoir, Parana River, Brazil, from September, 2001 to March, 2002, and from September, 2002 to February, 2003. The occurrence and numerical methods were applied for determining the occurrence frequency and numerical frequency of each food item in different standard length (SL) classes. The anterior digestive tract of C. jenynsii began to differentiate into the stomach at 4.70 mm SL (not presented pyloric caeca). Since the stage of pre-flexion, there are three intestinal folds and a lot of grooves in the digestive tract. The dietary analysis showed that the smaller larvae (class 1) had a distinct diet, with dominance of cladocerans (mainly Bosmina hagmanni and Bosminopsis deitersi). For class 2, the copepod Notodiaptomus sp. was important both in number and occurrence, however B. hagmanni also had significant importance in the diet. Already the largest larvae (classes 3 and 4) and juveniles (class 5) showed a similar diet, consuming mainly copepods (Notodiaptomus sp.). Therefore, in this study, larvae of C. jenynsii can be considered zooplanktivore, since in all stages of development, copedods and cladocerans dominated the diet. Changes in diet followed the morphological changes of the early stages of C. jenynsii.