Studies On The Feeding Biology And Energy Budget Of The Nemertean, Procephalothrix Simulus Iwata

Procephalothrix simulus Iwata, 1952 is one of the most common nemerteans along the coasts of Qingdao. In the present study, experiments were carried out to examine its chemoreception, feeding behavior and feeding rate, the effect of temperature and body weight on the energy budget and the protease activity.1. Studies on the chemoreception of the nemertean, Procephalothrix simulusThe feeding responses of Procephalothrix simulus Iwata to the whole-body extracts of different animals (Tubifex sp., Saccocirrus gabrillae) and single compounds (including 17 amino acids, 2 compounds related to amino acids and 2 sugars) were tested, and the response of the nemerteans with and without a frontal organ to stimulus was compared experimentally. Results showed that P. simulus is able to detect food from a distance by chemoreception. It preferred extracts to live prey, and boiled extracts were more attractive than extracts that were not boiled. Of the 21 compounds tested, 6 amino acids (glycine, alanine, isoleucine, phenylalanine, glutamine, asparagine) and betaine induced a feeding response, suggesting that they were possibly the chemical signals in the food location of P. simulus. When the frontal organ was removed, P. simulus apparently lost its selectivity, which indicated that in this nemertean chemoreception for the detection of prey was performed by the frontal organ.2. Laboratory observations on the feeding behavior and feeding rate of the nemertean, Procephalothrix simulusThe feeding behavior of the nemertean Procephalothrix simulus, and the effects of prey density, temperature, salinity and photoperiod on the feeding rates of this nemertean were experimentally studied. P. simulus, which detected preys by chemoreception, showed a typical macrophagous feeding strategy. When the prey was inactive (Tubifex sp., a freshwater oligochaete, which could be immobilized in seawater), all attacks made by P. simulus resulted in successful ingestions, and in 25% captures the nemertean did not evert its proboscis. When capturing active prey (Saccocirrus gabrillae, a marine polychaete), however, the nemertean worms always everted their proboscis and more than half of the attacks could not result in final ingestions. The experiment using size-screened nemerteans and preys revealed that when the body weight of nemerteans increased the rate of successful attacks increased, while the duration of the feeding events decreased. Present results also showed that the feeding rate of P. simulus might be significantly impacted by extrinsic factors. The feeding rate of P. simulus increased significantly when the temperature was elevated from 5°C to 30°C, but extremely high temperature (32°C) inhibited its predation; its food intake decreased significantly in media diluted to 20‰and 10‰and in medium with salinity as high as 45‰; but the salinity of 40‰did not impact the predation rate in this nemertean; dark conditions could induce higher food intake.3. Effects of temperature and body weight on the growth and energy budget of the nemertean, Procephalothrix simulusThe effect of temperature and body weight on the growth and energy budget of the nemertean Procephalothrix simulus were studied. The results showed that temperatures have significant effect on the weight gain, specific growth rate (SGR), food intake and food conversation efficiencies (FCE). The weight gain, SGR and FCE were highest at 20oC, but negative value was appeared at 30 oC; while the food intake was increased when the temperature elvated from 10 oC to 30 oC. Energy consumed in food (C), energy lost in feces (F), energy lost in excretion (U) and energy lost for respiration (R) were increased with the increasing temperature, while energy deposited for growth (G) was highest at 20 oC, an then decrased significantly in 30 oC, even appear negative value. The energy budget of nemertean showed that temperature have significant effect on the percentage of G to C, R to C and U to C, while for the percentage of F to C, the effect was not significant. In the body weight experiment, the results showed that body weight have significant effect on the weight gain, SGR and food intake, while it has no significant effect on FCE. When the body weight of the nemertean increased, the weight gain, SGR and food intake increased, while Energy consumed in food, energy lost in feces, energy lost in excretion, energy lost for respiration and energy deposited for growth decreased. Body weight has no significant effect on the allocation of the consumed energy.4. Studies on the protease activity of the nemertean, Procephalothrix simulusThe effects of temperature, pH and feeding on the protease activity of Procephalothrix simulus was studied by using enzyme analytical method. The results showed that the peaks of protease activities appeared at pH values of 3 and 10, and the activity of acid protease was higher than that of alkaline protease. The effect of temperature (20 oC -80 oC) on acid protease activity was different from that of alkaline protease. Acid protease activity reached the peak value at 50 oC; while for the alkaline protease, the optimal temperature was 40 oC, and the activity decreased rapidly when the temperature was elevated to 50 oC, which indicated that the alkaline protease was sensitive to high temperature. The results also showed that the protease activity of P. simulus varied significantly after feeding. After being elevated to its maximum value at 2 h after feeding, the activity of acid protease declined and reached the lowest value 8 h after feeding, but after that time the activity increased again and reached the equivalent value about 24 h after feeding. Alkaline protease, however, increased to the peak value at 8 h, and kept at low values 16h after feeding.