Effects of Steel Mill Scale on the strength characteristics of Expansive Clay Soils(Black Cotton Clay soil)

The results of laboratory investigations on the influence of Steel Mill Scale on the strength characteristics of tropical black cotton clay soils are presented. Tropical Black Cotton clay soils were mixed with Steel Mill Scale at 0%, 5%, 10%, 15%, 20% and 30% Steel Mill Scale content (by dry weight of soil) in order to establish the soil stabilizing potentials. Steel Mill Scale increased the Maximum Dry Density, MDD, of the soil by about 19% and reduced the Optimum Moisture Content, OMC, by about 28%. Soaked CBR increased with increase in Steel Mill Scale while Un-Soaked CBR decreased with increase in Steel Mill Scale content. Steel Mill scale increased the Un-soaked CBR by about 19% and reduced the Soaked CBR by about 75%. Swelling potential reduced by about 60% with the addition of Steel Mill Scale. Steel Mill Scale increased the unconfined compressive strength of black cotton soils by about 53% at 5% Steel Mill Scale content. The results indicate that there is a potential in the use of Steel Mill Scale to strengthen Black cotton soils. Keywords: Expansive soils, Black cotton clay soil, Steel Mill Scale, Strength Characteristic

Population dynamics of Chrysichthys nigrodigitatus (Lacépède, 1803) in Ikere-gorge, Oyo State, Nigeria

The growth and mortality parameters of Chrysichthys nigrodigitatus were estimated to assess the sustainability of its exploitation in Ikere-gorge, Oyo State, Nigeria. A total of 1210 of Chrys­ichthys nigrodigitatus were sampled from fishermen catches between January, 2017 and Decem­ber, 2018. C. nigrodigitatus were exploited with gillnet, cast net and traps (Malian trap net and bamboo). Total lengths were measured with fish measuring board. The FAO-ICLARM Stock Assessment Tool (FiSAT II) software was used to analyze length-frequency data of the fish. The estimated growth parameters are: asymptotic length is 60.9 cm, growth coefficient is 0.96, optimum length is 38.51 cm; length at maturity is 33.44 cm while length-at-first-capture is 12.62 cm. The estimated mortality parameters are: total mortality is 3.29 per year, natural mortality is 1.43 per year and fishing mortality is 1.86. It was observed that C. nigrodigitatus of Ikere-gorge were more vulnerable to exploitation at sizes less than their length at maturity. Likewise, the ex­ploitation rate (E = 0.57 yr-1) is greater than sustainable exploitation rate (Emax = 0.46 yr-1). This shows that exploitation of C. nigrodigitatus in Ikere-gorge is not sustainable. Therefore, there is need to reduce fishing pressure on C. nigrodigitatus to ensure its sustainability in Ikere-gorge

Estimation of gillnet selectivity of Coptodon zillii in Asejire Lake, Oyo State, Nigeria

Gillnet selectivity of Coptodon zillii was estimated in this study to determine the appropriate mesh size for the exploitation of the fish in Asejire dam. Holt’s indirect method of estimation was used to estimate gillnet selectivity of C. zillii in Asejire dam. Three mesh sizes 50.8mm, 63.5mm and 76.2mm were used for the estimation. The result shows that these mesh sizes caught C. zillii that were significantly different in sizes and abundant (P < 0.05). The 63.5 mm mesh size of gillnet was the most efficient; it caught 150 C. zillii with length range of 13 – 22 cm. Also, 50.8 mm mesh size caught137 C. zillii with length range of 11 – 18 cm. Likewise, 76.2 mm mesh size caught 57 C. zillii with length range 16 – 24 cm. The optimum length of 50.8 mm mesh size was 14.78 cm, 63.5 mm was 18.48 cm and 76.2 mm was 22.17 cm. Mesh size of 63.5mm is recommended as the appropriate mesh size for the exploitation of C. zillii in Asejire dam for the sustainability of the fish. This is done to prevent both recruitment and growth overfishing of C. zillii in Asejire dam. Key words: optimum length; exploitation; selection; sexual maturity; recruitment overfishing, growth overfishin