Effects of salinity level on the activity of chloride cell and mucus secreting cell in the gill of the female Shortfin molly, Poecilia mexicana Steindachner, 1863

Ovoviviparous poeciliid fishes have been relatively well studied in the unique reproductive strategy, but their osmoregulatory system largely remains unknown. In this study, we conducted a short-term (7 days) lab experiment to investigate the effect of different salinity levels from 0 (freshwater) to 50 ppt (mesosaline) on the number of chloride cells and mucus secreting cells of female Poecilia mexicana. The density of chloride cells and mucus secreting cell were also arranged along the epithelial lamellae in wild fish. More interestingly, the average density of chloride cells and the mucus secreting cell were mostly differed between these levels (P < 0.05). Integrative data from our study suggested that the potential function of the osmoregulatory mechanism/strategy was supported by chloride and mucus secreting cells of female P. mexicana gill.

HISTOPATHOLOGY STUDIES OF SELECTED ORGANS OF Hemichromis fasciatus INHABITING IGUN GOLD MINING AND OPA RESERVOIRS, OSUN STATE, NIGERIA: A COMPARATIVE STUDY

This study examined the histopathological alterations in the gills, fillet and liver of Hemichromis fasciatus in Igun reservoir (located in an abandoned goldmine area) compared to those of Opa reservoir. Life fish species were collected from Opa and Igun reservoirs and identified in the laboratory. Techniques based on histological analyses were done on the organs and photomicrographs taken using digital binocular compound LED microscope. Epithelial lifting and hypertrophy of lamellae were observed in the gills of H. fasciatus in Opa reservoir and compared to rupture of gill epithelium, rupture of chloride cell, fusion, hyperplasia, curling of lamellae in H. fasciatus of Igun reservoir. The fillet of H. fasciatusin Opa and Igun reservoirs revealed splitting and atrophy of muscle bundles. Also, parasite cyst and necrosis were observed in the fillet of H. fasciatus of Igun reservoir compared to degeneration in muscle bundles in the fish of Opa reservoir. Similarly, the liver of H. fasciatus in Igun and Opa reservoirs showed splitting at the wall of central vein, hepatopancreas and liver cells degeneration. Moreover, nucleus hypertrophy was also identified in the liver of H. fasciatus in Opa reservoir compared to vascular congestion in the central vein, bile duct, portal vein and portal artery of H. fasciatus in Igun reservoir. The study therefore concluded that H. fasciatus specimens in Igun reservoir were histopathologically unhealthy as compared with those of Opa reservoir probably due to the high level of pollution resulting in bioaccumulation of heavy metals in Igun reservoir samples. Obayemi, O. E | Department of Zoology, Obafemi Awolowo University, Ile-Ife, Osun State, Nigeria

The effect of salinity on osmoregulation and development of the juvenile fat snook, Centropomus parallelus (POEY)

Eurihaline fish support waters with different salt concentration. However, numerous studies have shown that salinity can affect fish development. Thus, the effect of salinity change from 20 to 5 and 35 on survival, weight, length, gill chloride cell ultrastructure and gill Na+, K+ ATPase activity was evaluated in Centropomus parallelus following short-term (6, 24 and 96 hours) and long-term exposure (30 and 60 days). Salinity did not affect C. parallelus survival, final weight and length. The quantity of chloride cells increased visibly at salinities of 5 and 35, with the cells exhibiting the typical features of uptake and secretory cells, respectively. Na+, K+ ATPase activity in the gill of the C. parallelus was significantly greater at a salinity of 5 than at a salinity of 20 or 35 after 96 hours, but not after 30 or 60 days. These results indicate that salinity change from high to low salt water induces gill chloride cell and Na+, K+ ATPase activity adaptations after short-term exposure. However, after long-term exposure at salinity 5, gill Na+, K+ ATPase activity is no more necessary at high levels. The increase in salinity to 35 does not induce significant change in gills. Juveniles of C. parallelus may thus be capable of acclimating to salinities of 5 to 35 for 60 days without significant effects on development.