Study On The Feeding Behavior Of The Tonguefish Cynoglossus Semilaevis Günter

Cynoglossus semilaevis Günter, a flat fish deep water species, is a high-nutrition and economic valued species and currently cultured widely in China. In order to solve the difficult problem of feeding and facilitate feeding of C. semilaevis, in the paper, the feeding behavior of C. semilaevis is detailedly studied by the methods of behavioral science experiment, nutrition-physiology and histology, the main results and conclusions are as follows:1. Sense utilization of feeding behavior in Cynoglossus semilaevis GünterThe feeding behavior of C. semilaevis was investigated by selective elimination or inhibition of eyes,lateral line and nose and observing the behavioral response of the fish to visual,mechanical and chemical stimuli under laboratory conditions. It is shown that C. semilaevis attacks mainly its preys by lateral line sensing. When the lateral lines were working, the olfaction co-works, depending partially on the feeling by fins and head. The taste sense is used when snap and swallow. The lateral lines play effective role on preying, which may explain why C. semilaevis feed artificial diets unwillingly that supplied in normal schemes.2. Function mechanism of vision during the feeding behavior of C. semilaevisThe structure of the retina and visual characteristics of C.semilaevis from newly -hatched larvae to 50- day old juveniles, and at 50 mm total length young fishes, was examined. The main results obtained are as follows: The retina of C.semilaevis in larva consists mainly of single cones as sensory cells with a high density; the rods and twin cones appear rather late. Over the whole range of development, the density of cones and ganglion cells decreases while the density of the rods increases correspondingly. The data concerned shows that the structure of the retina apparently changes in the stage between 20- and 31-day old juveniles, which is a transitional period in which its visual characteristics changes obviously. It is revealed that the changes of visual structure of C.semilaevis are adapted to the ecological shift from pelagic to benthic habitats. The structure of the internal nuclear layer of C.semilaevis is highly peculiar: a 50 mm C.semilaevis has only a layer of horizontal cells, its sensitization system is underdeveloped. In addition, it has 4–5 layers of bipolar cells and amacrine cells. However, it is difficult to distinguish the two kinds of cells. Obviously, the decrease in layers of the internal nuclear layer as well as bipolar,amacrine and ganglion cells, which are not well-differented, showing that the retina of C.semilaevis is not sensitive to light. The acuity of larvae in the pelagic stage is comparatively high,vision play a very significant role in feeding behavior. After benthic habitats, both the acuity and the light sensitivity are weak; therefore, vision does not have an important effect on feeding behavior.3. Function mechanism of mechanism sense during the feeding behavior of C. semilaevisThe lateral-line sense organs and dermal surface unusual structure on the abocular side of C. semilaevis were examined by using light and scanning electron microscopic techniques. Results have showed, that on the ocular side: the canal pores of C. semilaevis are round, the diameter of canal pore is exactly equal to that of the lateral-line canal at the same place, every canal pore connects with one colloid canal which extend into the lateral-line canal, the unusual structure can improve the sensitivity of canal organs (canal neuromasts). The widest diameter of both canal pores and lateral-line canal as well as the highest density of canal pores occur around the mouth of C. semilaevis, these characteristics indicate that the sensitivity of canal organs (canal neuromasts) around the mouth is the highest and they play a highly important role in the feeding behavior .that on the abocular side: a sort of astonishing papilla was found on the abocular side of the head, they are enchased on the skin surface .What is their most surprising feature is that a shield-shaped mantle with flanges is wrapped across the top of the papilla. According to their exterior shape and their interior structure, the author supposes that they are of a sort of touch receptor not described before and should make important difference to the feeding behavior of C. semilaevis. 4. Function mechanism of chemistry sense during the feeding behavior of C. semilaevis4.1 Function mechanism of olfactory sense during the feeding behaviorMorphology and structure of olfactory organ of C. semilaevis were systematically investigated by means of measurement and light and scanning electron microscopic techniques. The results were as follows: Olfactory sacs on either side differ in size and number of lamellae. The sac on the abocular side is smaller and contains fewer lamellae. Surface morphology of lamellae in different position of the olfactory sac is not the same. Reference four types of distribution patterns of the sensory epithelium on the lamellae surface (Yamamoto, 1982), the lamellae on the front part of olfactory sac and the lamellae on the rear part of olfactory sac are respectively named TypeⅠ′and TypeⅣ′lamellae(Fig.5)by the author, at the same time ,the author think that the sensitivity of TypeⅠ′lamellae is slightly weaker than that of TypeⅠlamellae and the sensitivity of TypeⅣ′lamellae is weaker than that of TypeⅣlamellae (Fig.4,Fig.5).According to the average ratio of the length of the olfactory sac to the eye diameter, the mean number of lamellae,distribution patterns of the sensory regions and non-sensory regions on the lamellae surface,the author propose that olfactory organ of C. semilaevis is comparatively developed.4.2 Function mechanism of gustatory organ during the feeding behaviorThe relation between morphology, distribution and function of the oropharyngeal cavity gustatory organ of C. semilaevis were investigated by using scanning electron microscopic and behavioural experiments methods. Scanning electron microscopic studies revealed that the distribution of the gustatory organ is comparatively concentrative, and TypeⅠtaste buds were located on the inner surface of the snout tip while those of TypeⅡwere mainly found on the upper surface of both the front and the central part of the tongue. Behavioral experiments showed that both TypeⅠand TypeⅡtaste buds were sensitive to both chemical and mechanical stimuli, and the texture of the food is as important as its chemical nature to the fish. It is suggested that TypeⅠand TypeⅡtaste buds do have the function of mechanoreception as well as chemoreception.5. Conclusion and advice5.1 According to the results of the behavioral science experiment, nutrition - physiology and histology, the conclusions of the author are as follows: in ocean, C. semilaevis attacks mainly its preys by lateral line sensing, when the lateral lines were working, the olfaction co-works, and vision make hardly any difference to the feeding behavior. In addition, the taste sense is used when snap and swallow. Although result from histology show that olfactory organ of C. semilaevis is comparatively developed, the author still deem the results of the behavioral science experiment, nutrition– physiology, namely, the lateral lines play highly important role on preying. About the skin superficial papilla of C. semilaevis head, the author suppose that they are of a sort of touch receptor not described before and should make important difference to the randomicity feeding behavior of C. semilaevis.5.2 In order to solve the difficult problem of feeding and facilitate feeding of C. semilaevis, the feeding behavior of C. semilaevis is detailedly studied. Owing to C. semilaevis attacks mainly its preys by lateral line and olfaction play a supplementary function,thereby, in order to improve the feeding of C.semilaevis, both stimulating the chemistry sense organ and stimulating the mechanism sense organ all should be considered.