A PRELIMINARY ANALYSIS ON THE FOOD HABIT OF XENOCYPRIS DAVIDI BLEEKER IN RESERVOIR GUANTING

Xenocypris davidi (Bleeker) in the Reservoir Guanting changes its food habit correspondingly with the development of gill rakers and intestine. Under 11.8 mm in body-length, the fry has its mouth superior in position and gill rakers few in number, with straight intestine. It ingests rotatoria and blue-green algae. When body-length reaches 11.8—12.3 mm, gill rakers begin to differentiate and intestine appears to have 1—2 windings. Fry at this stage feeds on small-cladocerans with Moina being the main food. Fry reaching 15.8—17.4mm in bodylength has its mouth directed forward. The gill rakers become a network and the intestine has 4—8 windings with enlarged fore intestine. Its main food includes organic debris, chironmids and blooming algae such as Euglena and blue-greens. Beyond 18 mm in length, mouth of the fingerling has totally turned downward and the development of gill rakers and intestine are almost complete. Fingerlings become benthic in behavior. Of those young fish, the percentage composition of food items (wet-weight) in fore intestine was soil and sand particles 50.6%, organic debris 40.0%, chironmids 6.2% and plankton 3.2% Adult fish of Xenocypris davidi in the Reservoir Guanting feeds on a greet deal of organic debris and a small quantity of benthic diatoms and Oscillatoria. Relative composition of food (in wet-weight) in the fore intestine was calculated as: inorganic particles 23.1—89.8%, organic debris 9.7—76.9%, benthic diatom and Oscillatoria 0.003—2.6%. Inorganic particles and benthic algae were found in greater quantity in spring, stunmer, and autumn, while organic debris was more abundant in winter. It relates to the environmental conditions of its habits. Nutritional value in the food stuff of adult fish is considered to be very low, containing onty 0.37% of total-N, and 4.8% of organic substance, and the energy in a gram of food in wet-weight is merely 146.35 Cal. To cope with the shortage of nutrients, fish must keep on feeding all year round, even in winter. Owing to this biological feature, stocking X. davidi in reservoir isan effective measure to increase fish yield Xenocypris davidi.