STRUCTURE OF THE DIGESTIVE TRACTUS IN ARISTICHTHYS NOBILIS

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1 Lucrări ştiinţifice - vol. 51 seria Zootehnie STRUCTURE OF THE DIGESTIVE TRACTUS IN ARISTICHTHYS NOBILIS Gabriela VASILE, Gianina COMĂNESCU, Elena CIORNEA The paper presents some histological aspects of the digestive tractus in Aristichthys nobilis in its various segments (anterior post-oesophagian intestine, anterior distal intestine, median and posterior intestine), as correlated with both age and main type of food for the species under study. The digestive tube has been taken over form 5 Aristichthys nobilis individuals of various ages, namely: one- and four-old summer ones, the digestive tractus being unfolded along its whole length, after which rectangularly-shaped fragments were taken over and processed by methods of histological techniques; thus, the nuclei were colored with hemalaune, while the cytoplasm - with eosine. Thickness of the mucous and muscular tunics was measured by the micrometric method, with a micrometric objective thin plate lamina and an ocular micrometric lamina. The experimental results obtained put into evidence some variation in the form of the mucous folds (simpler in one summer-old individuals and more complex in the four summer-old ones), along with variations in the thickness of the mucous and muscles. For both categories of ages taken into study, the mucous and muscular tunics are more well-developed in the segment of the post-oesophagian anterior intestine than in the rest of the digestive tractus, which entitles one to consider this portion as a stomach, in spite of the typically intestinal aspect of the mucous tunic. MATERIALS AND METHOD As the studies devoted to the morpho-structural aspects of the digestive tractus in Asian cyprinids are quite few and very synthetic (BERRY and LOW, 1970; BREMER, 1978; TREVISAN, 1979; ATHIKESAVAN et al., 2006), the present investigation analyzes such aspects in bighead carp (Aristichthys nobilis) of various ages, i.e., one and four summer-old individuals, for evidencing some possible intraspecific (age-dependent) similarities or differences. The digestive tube has been taken over form five Aristichthys nobilis individuals of various ages, namely: one- and four-old summer ones, the digestive tractus being unfolded along its whole length, after which rectangularly-shaped fragments were taken over and processed by methods of histological techniques; thus, the nuclei were colored with hemalaune, while the cytoplasm - with eosine (HUMASON, 1962; MARTOJA and MARTOJA, 1967). Thickness of the mucous and muscular tunics was measured by the micrometric method, with a micrometric objective thin plate lamina and an ocular micrometric lamina (MUREŞAN et al., 1974)

2 Universitatea de Ştiinţe Agricole şi Medicină Veterinară Iaşi RESULTS AND DISCUSSION In one summer-old bighead carp representatives, one may observe that - in the post-oesophagian portion of the anterior intestine - the mucous tunic evidences a few folds with cylindroidal aspect, lying on the surface of the mucous tunic. Besides them, other smaller, conical-shaped folds may be observed, their axis evidencing the corione infiltrated with lymphocytes while, in the cylindroidal shaped folds, the corione hardly penetrates (Fig. 1). On its whole, the corione of the mucous tunic is totally infiltrated with lymphocytes - even some lymphatic follicles being observed in its thickness (Fig. 2). Fig.1. Cross-section through the anterior post-oesophagus intestine of one summer-old Aristichthys nobilis (assembly; 100x) (original photo) Fig.2. Cross-section through the anterior post-oesophagus intestine of one summer-old Aristichthys nobilis (detail: lymphatic follicle from the corione mucous thickness; 200x) (original photo) In this segment, the height of the mucous tunic is of µm. The mucous, calyx -shaped cells from the epithelium are not very numerous. As to the muscular tunic, both the circular and the longitudinal layers have a thickness of µm

3 Lucrări ştiinţifice - vol. 51 seria Zootehnie In four summer-old organisms, the portion of the anterior postoesophagian intestine is especially well-developed, the mucous tunic being high, with ample folds, most of them cylindroidal in shape, with a rich epithelium, high and rich in calyx-shaped cells in full activity. The corione of the mucous tunic is intensely impregnated with lymphocitary elements, which supports the idea that an intense immunitary activity is developing in this segment of the digestive tractus, probably determined by the type of food which - in the opinion of several authors - is constituted, predominantly, of zooplankton (LAZAREVA et al., 1977; MARCIAK and BOGDAN, 1979; CUI et al., 2005). As to the apical part of some of the mucous tunic's folds, it has been observed that, here and there, it is folded and eroded, the erosions evidencing some repression from the part of the intensely lymphocyte impregnated corione. Very well represented is also the muscular part of the mucous tunic, while the sub-mucous tunic is weakly evidenced (Figs. 3-4). On the whole, the thickness of the mucous tunic is of µm. As to the muscular tunic, it is wellevidenced at this level - especially the internal, circular layer - the thickness of this tunic being of 625 µm. Fig.3. Cross-section through the anterior post-oesophagus intestine of four summer-old Aristichthys nobilis (assembly; 100x) (original photo) Fig.4. (Cross-section through the anterior post-oesophagus intestine of four summer-old Aristichthys nobilis (detail: repression of the lymphocyte impregnated corione; 200x) (foto original)

4 Universitatea de Ştiinţe Agricole şi Medicină Veterinară Iaşi In the distal part of the anterior intestine, in one summer-old Aristichthys nobilis representatives, the mucous tunic is relatively high, with a thickness of 250 µm, evidencing folds of various shapes. The epithelium is extremely thin, while the calyxshaped cells are not visible. The corione is lax, with slight lymphocytary infiltrations. Again, at this level, a lymphocyte mass may be observed, migrating inside the lumen of the respective cavity; the muscular tunic is thin, of µm (Fig. 5). Fig.5. Cross-section through the anterior distal intestine of one summer-old Aristichthys nobilis (assembly; 200x) (original photo) In four summer-old Aristichthys nobilis individuals, the distal segment of the anterior intestine evidences a very high mucous tunic, with folds of various shapes - some of them cylindrical, others conical and even trapezoidal - with a very high prismatic epithelium, very rich in calyx-shaped cells; the striated plateau of the epithelium is highly visible. In the axis of these folds, the corione is sufficiently well-represented, being strongly impregnated with lymphocytes. Such lymphocytary infiltrations penetrate the epithelium, as well, trying to reach the intestinal lumen. The presence of some lymphatic follicles may be also observed in the thickness of the corione (Figs. 6-7). Fig.6. Cross-section through the anterior distal intestine of four summer-old Aristichthys nobilis (assembly; 100x) (original photo)

5 Lucrări ştiinţifice - vol. 51 seria Zootehnie Mention should be made of the fact that the presence of such lymphocytary infiltrations inside the mucous tunic may be related to the abovementioned immunitary activity, correlated with the type of food, once known that the Aristichthys nobilis consumes mainly zooplankton (cyclopes, copepods, chladoceres, kelicerates) with keratinous cover which, in most cases, cause lesions at the level of the mucous tunic's epithelium. On its whole, the thickness of the mucous tunic is of 1000 µm; in this case, too, the muscular part of the mucous is very well represented, its thickness being of µm. Fig.7. Cross-section through the anterior distal intestine of four summer-old Aristichthys nobilis (detail: lymphatic follicle; 200x) (foto original) In one summer-old bighead carp individuals, in the segment of the medium intestine, the mucous tunic is the most evident one, showing either conic or bifurcated folds, with a high epithelium, the calyx-shaped cells of this level being weakly represented; the corione is lax, weakly-impregnated with lymphocytes (Fig. 8). The height of the mucous tunic in this segment of the digestive tractus is of 250 µm, while the muscular tunic is µm thick. Fig.8. Cross-section through the medium intestine of one summer-old Aristichthys nobilis (assembly; 200x) (original photo)

6 Universitatea de Ştiinţe Agricole şi Medicină Veterinară Iaşi In four summer-old individuals, the segment of the average intestine evidences a well-developed mucous, with folds of various shapes - some of them cylindrical, others amply trapezoidal - covered by a prismatic epithelium with a striated plateau, very rich in calyx-shaped cells in full activity. Both the corione and the epithelium evidence strong lymphocitary infiltrations, very big lymphatic follicles - some of them of µm in size (Fig. 9) - being visible in the trapezoidal folds. Fig.9. Cross-section through the medium intestine of four summer-old Aristichthys nobilis (assembly; 100x) (original photo) At this level of the digestive tube, a strong erosion in the epithelium of the mucous tunic may be noticed, together with lymphocytes migration towards the intestinal lumen (Fig. 10). The thickness of the mucous tunic is, on the whole, of 625 µm, the muscular one being also relatively well-developed - with a thickness value of 375 µm. Fig.10. Cross-section through the medium intestine of four summer-old Aristichthys nobilis (detail: mucous erosion and lymphocytes migration towards the intestinal lumen; 200x) (foto original)

7 Lucrări ştiinţifice - vol. 51 seria Zootehnie In one summer-old Aristichthys nobilis individuals, the posterior intestine shows a thin wall, with a less high mucous tunic, of 87.5 µm, with small and dense folds, a hardly visible epithelium and a very lax corione, weakly impregnated with lymphocytes. The muscular tunic is extremely thin, of only 37.5 µm (Fig. 11). Fig.11. Cross-section through the posterior intestine of one summer-old Aristichthys nobilis (assembly; 400x) (original photo) The posterior segment of the digestive tractus - in four summer-old bighead carp representatives, with a µm thick mucous tunic, evidences numerous calyx-shaped cells, being intensely folded, most of the folds being cylindroidal in shape, while others are trapezoidal, the latter's corione being intensely infiltrated with lymphocytes; otherwise, the corione appears less infiltrated with lymphocytes. At this intestinal level, the muscular tunic is 250 µm thick (Figs.12-13). Fig.12. Cross-section through the posterior intestine of four summer-old Aristichthys nobilis (assembly; 200x) (original photo)

8 Universitatea de Ştiinţe Agricole şi Medicină Veterinară Iaşi Fig.13. Cross-section through the posterior intestine of four summer-old Aristichthys nobilis (detail: epithelium with striated plateau and calyx-shaped cells; 400x) (foto original) As evidenced by the graphical plot, as well (Figs ), both in the stage of fingerlings and at ages of four summers, the thickness of the mucous and muscular tunics generally record decreasing values along the length of the digestive tractus, starting from the post-oesophagian segment of the anterior intestine, up to the level of the posterior intestine, with the only exception of the muscular tunic (Fig. 15) which, in the one summer-old individuals, remains constant in the first two segments under investigation, with a thickness value of µm, after which - at the level of the medium intestine - records a slight increase in thickness (of 25 µm), comparatively with the segment of the distal anterior intestine, attaining a value of µm, which is probably due to the fact that - at the level of the posterior intestine - the muscular tunic is extremely thin (37.5 µm), a compensation being therefore possible as to the advancing activity of the content of the final intestine. Fig.14. Graphical representation of the thickness of mucous tunic in one summer-old Aristichthys nobilis individuals

9 Lucrări ştiinţifice - vol. 51 seria Zootehnie µm ant. post-oesoph. int. ant. distal int. mediu int. posterior int. Fig.15. Graphical representation of the thickness of muscular tunic in one summer-old Aristichthys nobilis individuals µm ant. post-oesoph. int. ant. distal int. mediu int. posterior int. Fig.16. Graphical representation of the thickness of mucous tunic in four summer-old Aristichthys nobilis individuals Fig.17. Graphical representation of the thickness of muscular tunic in four summer-old Aristichthys nobilis individuals

10 Universitatea de Ştiinţe Agricole şi Medicină Veterinară Iaşi CONCLUSIONS One of the main observations made on the microscopic structure of the various segments of the digestive tractus, in Aristichthys nobilis, as well as on their micrometric thickness values, refers to the fact that the aspect of the tunics (the mucous and the muscular one, especially) get modified as a function of age. Variation in the shape of the mucous tunic s folds (simpler in one summer-old individuals and more complex in four summer-old ones) was also observed, alongwith variations in the thickness of the muscular and mucous tunics (lower micrometric values in one summer-old individuals and higher micrometric values in four summer-old ones). For both categories of ages taken into study, the mucous and muscular tunics are more well-developed in the segment of the post-oesophagian anterior intestine than in the rest of the digestive tractus, which entitles one to consider this portion as a stomach, in spite of the typically intestinal aspect of the mucous tunic. REFERENCES 1. ATHIKESAVAN, S., VINCENT, S., AMBROSE, T., VELMURUGAN, B., Nickel induces histopatological changes in the different tissues of freshwater fish, Hypophthalmichthys molitrix (Valenciennes), J. Environ. Biol., 27 (2): BERRY, P. Y., LOW, M. P., Comparative studies on some aspects of the morphology and histology of Ctenopharyngodon idella, Aristichthys nobilis, and their hybrid (Cyprinidae), Copeia, 4: BREMER, H., Histological and histochemical studies on the detection of the esogaster in the agastric cyprinidae Aristichthys nobilis Rich. (Marble carp), Gegenbaurus Morphol. Jahrb., 124 (5): CUI, F. Y., LIN, T., LIU, D. M., ZHANG, L. Q., Excess propagation and biological control of zooplanktonic Cyclops in drinking water sources, Water Sci. Technol., 52 (8): HUMASON, L. G., Animal tissue techniques, W. H. Freeman and Company, USA, 468p. 6. LAZAREVA, L. P., OMAROV, M. O., LEZINA, A. N., Feeding and growth of the bighead carp, Aristichthys nobilis, in the waters of Dagestan, Journal of Ichthyology, 17 (1): MARCIAK, Z., BOGDAN, E., Food requirements of juvenile stages of grass carp, Ctenopharyngodon idella Val., silver carp, Hypophthalmichthys molitrix Val., and bullhead carp Aristichthys nobilis Rich., EMS Special Publication, 4: MARTOJA, R., MARTOJA, M., Initiation aux techniques de l histologie animale, Éd. Masson et Cie, Paris, 345 p. 9. MUREŞAN, E., GABOREANU, M., BOGDAN, A. T., BABA, A. I., Tehnici de histologie normală şi patologică, Ed. Ceres, Bucureşti, 478 p. 10. TREVISAN, P., Histomorphological and histochemical researches on the digestive tract of the freshwater grass carp, Ctenopharyngodon idella (cypriniformes), Anat. Anz., 145 (3):