| Different kinds of methods including electro-olfactogram (EOG), gustatory facial nerves recording, behavioral methods (biting-balls), feeding trial were used for the evaluation of feeding stimulants for gibel carp (Carassius auratus gibelio). Amino acids, nucleotides, organic acids and other potential stimulants were tested. Electro-olfactogram responses of 22 stimuli at the concentrations of 10-8g/l to 10-2g/l and gustatory facial nerves responses of 22 stimuli at the concentrations of 10-8mol/l to 10-2mol/l were investigated. The potential feeding stimulants were then evaluated by behavioral methods. The adaptation of fish to feeding stimulants was then investigated.The main results are shown as the following.1. Waveforms of olfactory and gustatory electrophysiological responses to different feeding stimuli were transient, rapidly adaptive, biphasic discharges. Olfactory waveforms reversed at certain concentrations and reversal waves of different stimuli appeared at different concentrations. Phenylalanine, proline, threonine only obtained one type of waves.2. Magnitudes of olfactory and gustatory responses increased exponentially with the increase in stimuli concentrations. Magnitudes of the responses to inosine, hypoxanthine and trimethylamine hydrochloride showed no significant variation with the increase in stimuli concentrations. 3. Durations of olfactory response increased with the increase in stimuli concentrations. No changes were found in gustatory response durations. Response durations of proline, alanine, valine, threonine, argnine and hypoxanthine showed no significant difference at different concentrations.4. Thresholds of olfactory responses were from 10-6g/l to 10-5g/l while those of guastatory responses were from 10-6mol/l to 10-5mol/l. Responses of threonine, inosine, betaine, histidine, valine, asparagic acid, proline, taurine, lactic acid did not show the satiation in EOG responses. No satiation was found in gustatory responses to most of stimuli. Satiation concentrations were 10-3g/l in olfactory response and 10-3mol/l in gustatory response, respectively.5. Electrophysiological responses of olfaction and gustation were dose-depended. Amplitudes of different stimuli showed different orders at different concentrations. The most potential olfactory stimulants were lactic acid, asparagic acid, arginine, lysine, alanine and synthetic mixture while gustatory stimulants were lysine, glycine and lactic acid.6. The best stimulant in behavioral trials was asparagic acid, then arginine and threonine. Less stimulative effect were showed in other stimuli. Most of stimuli were ineffective on behavioral response of gibel carp. Lactic acid was repellent for big fish (46.9±11.2g), but stimulant for small fish (6.9±0.3g).7. The most effective compound were 10-4 g/kg asparagic acid+threonine (26:63) or 10-4 g/kg asparagic acid+threonine+DMPT(26:63:10).8. Feeding stimulants could increase feeding rate of gibel carp during feeding trial. 10-4 g/kg asparagic acid+threonine+DMPT(26:63:10) could increased feeding rate by 22% in first 2 weeks. No significant difference of feeding rates between test diet and the control diet was observed in 4 weeks.9. Changing feeding stimulants could significantly affect fish feeding rate. Feeding rate could be significantly increased by the inclusion of 10-4 g/kg asparagic acid+threonine+DMPT (26:63:10) in diet while reduced when it was replaced by other stimulants. Feeding rate stabilized next day after changing diet.10. Total specific growth rate, feeding rate and body dry matter, crude protein, crude lipid, ash were not affected by the changing of different feeding stimulants while fish gross energy were significantly affected.In conclusion, it is effective to screen feeding stimulants by electrophysiological, behavioral methods and feeding trial. Feeding stimulants can significantly increase feeding rate of gibel carp. However, fish could adapt to the diet after a long-term rearing.
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