ECOLOGICAL STUDIES OF CHRYSICHTHYS NIGRODIGITATUS (LACEPÈDE, 1803) AND OREOCHROMIS NILOTICUS (TREWAVAS, 1983) IN ASEJIRE RESERVOIR AND LAGOS LAGOON, SOUTH-WEST NIGERIA

Abstract

Ecological studies were carried out in Asejire Reservoir (AR) and Lagos Lagoon (LL), Southwest Nigeria from January 2012 to December 2013 to determine the health status of Chrysichthys nigrodigitatus (CN) and Oreochromis niloticus (ON) Some physical and chemical parameters such as air and water temperature (0C), transparency (m), depth (m), turbidity (m), pH, DO (mg/l), salinity (%0), conductivity (μScm) of the waterbodies were determined. The fish species samples were collected on monthly basis, these were separated into sexes, and growth pattern {length, (cm); weight (g), Isometric index, condition factor} were measured. Haematology indices of fish species were determined. Heavy metals (lead (Pb), iron (Fe), zinc (Zn), copper (Cu), and chromium (Cr) in ppm concentrations were also determined while bacteria occurrence(s), (load and prevalence) on fish skins, gills and intestine in the two ecological zones were determined. The physico-chemical parameters determined revealed environmental similarity of the waterbodies such as in air and water temperatures as well as pHvalues. Fish ratio collected is in range with normal aquatic (1: 1+) male: female ratio. Growth assessment determined revealed no significant difference in length and weight in O. niloticus between locations; but significant difference in weight occurred in C. nigrodigitatus between locations, with higher weight (196.06 ±0.16 g) from Lagos Lagoon. Highest condition factor (5.25) was recorded in Asejire Reservoir O. niloticus, (ARON); and lowest condition factor (1.64) was observed in Asejire Reservoir C. nigrodigitatus (ARCN); as this indicated a negative allometric value which is normal in Bagridae species because it increases more in Length to weigth gain than for the Cichlidae growth status. Normal growth rate (K > 1) occurred between sexes, with the male species having higher K - factors than female species within locations, between locations, between species, and within species, except for female C. nigrodigitatus having higher condition factor (K = 1.75) than male C. nigrodigitatus (K = 1.54) in Asejire Reservoir. Highest isometric value (3.05) was recorded in Asejire Reservoir O. niloticus and lowest in Lagos Lagoon C. nigrodigitatus. Male O. niloticus from Asejire Reservoir had highest isometric value, and O. niloticus species had higher condition factor which ranged between isometric (b ≤ 3) and positive allometric (b > 3), hence, denoted robustness of fish to grow more in weight than in length; while C. nigrodigitatus fish has negative allometric (b < 3) indicating fish add more length than in weight on growth. The status of condition factors and isometric values obtained is species specific, and environmental influence, food availability or reproduction factor may as well be contributing factors. Haematology indicated that parameters determined falls within normal range among species; but there occurred significant relationship between mean White Blood Cell (WBC) determined only in LLON and ARCN; and highest WBC (7460.32±0.61) was determined in Lagos Lagoon C. nigrodigitatus (LLCN). Significant relationship occurred within location and not within species in Eosinophil values, and highest mean Eosinophil (1.67 ± 0.02) occurred in LLCN is indicating probable stress condition. The concentrations of heavy metals in fish flesh revealed that Zn (6.52 ±0.82) had highest, while Cr (0.01±0.00) was ranked lowest; for O. niloticus in Asejire Reservoir. In Lagos Lagoon, heavy metals concentration level revealed that O. niloticus flesh had highest in Zn (4.71±0.25) and lowest in Pb (0.01±0.00). Lagos Lagoon C. nigrodigitatus heavy metal concentration level revealed Zn (9.56±0.96) had highest, while Cr (0.06±0.01) had lowest; and Asejire Reservoir C. nigrodigitatus heavy metal level revealed that Zn (8.26 ±0.74) had highest, and Cr (0.08±0.00) had lowest. In all, Zinc (Zn) was top-ranked in level among species. Bacterial isolates revealed no significant difference in flora occurrence between species, within location and between locations; but significant difference occurred in O. niloticus from the two locations. While O. niloticus had higher bacterial frequency than C. nigrodigitatus; Lagos Lagoon had higher bacterial frequency than Asejire Reservoir. Micrococcus lectus was most abundant (75%) in the intestines and on the skins and gills; within specie and between species and locations. Hence, Asejire Reservoir and Lagos Lagoon environments showed traces of pollutants which can induce stress, and on the long term affect optimum production and functions of the fish species. Therefore, management practices for environmental sanitation will influence optimum growth in fish species, that will be proper food for public health.