Seasonal Changes in the Number of Dahlgren Cell in the Spinal Cords of Two Fish species and Their Cyclic Activity

Seasonal Changes in the number of Dahlgren cells in the spinal cords of two Freshwater fishes namely: Barbus luteus and Capoeta trutta were investigated along with their cyclic activity as detected using three different stain, Harris Haematoxyline –eosin (H-E), Aldehyde haematoxyline technique, (AF), Mallory triple stain, Amonical silver nitrate. These fishes were caught from River Tigris passing through Mosul city. After random counting of Dahlgren cells in the spinal cord of the 3 year old fish (B. luteus) three types of cells can be distinguished according to their sizes; small, medium and large. Small Dahlgren cells of B. luteus were most dominant in summer (average 81.6) then the number decreases in autumn, and then the minimum was in winter. The median sized cells were also large in number in summer (19.3), then the number was less than that in spring then winter and the lowest was in autumn. The large Dahlgren cells were more abundant also in summer (16), and less than that in spring, then in autumn, then the lowest was in winter. Dahlgren cells of C. trutta at age of 3 year, small cells were dominant in summer (79.67), and less than that in autumn, and lesser in spring. The medium sized cells were also dominant in summer (30.65), then spring, then autumn, while the large cells were dominant in spring (11.75). Anyhow, as seen above, the large number of Dahlgren cells were observed in summer especially small, then medium while large cells were more in spring. In B. luteus small Dahlgren cells were dominant in age 1 year, then 3 year, then 6 years, while medium sized cells were dominant in year 1, then 3, then 6 years. Generally number of Dahlgren cells decreases especially large once with increased age of B. luteus and C. trutta while Dahlgren cells of V. trutta was higher in number in age 1 year, then 3 year, then 6 year. Anyhow, the median and small size cells decreases in number as age of fish increases. It was revealed from the present study that Dahlgren cells possess secretory materials in the cytoplasm, their distribution and staining affinity varies from one type to other in both species of fishes investigated. The secretory cycle can be categorized into three stages: Stage I: mostly empty of few secretory material. Stage II: secretory material increase in cytoplasm far from nucleus. Stage III: discharge of secretory material from cell and its axon.