Comparative study of monofilament and multifilament gillnets in Lake Kainji

Comparative studies of monofilament and multifilament gillnets in Lake Kainji was carried out at Monai fishing village of Lake Kainji. A total number of six nets (3 multifilament and 3 monofilament gillnets) each measuring l5 meters in length and 3 meter depth were constructed; Kuralon ropes were used as footrope and headrope, synthetic corks as float and lead as weight. The net were set in the evening (between 5:00pm and 6:00pm) and hauled in the morning (between 8am and 9am) thereby maintaining a soaked time of about l5 hours.The species captured were: Oreochromis niloticus, Oreochromis aureus, Sarotherodon galileus, Tilapia mariae, Synodontis nigaita, Alestes baromoze, Distichodus rostratus, Tilapia dageti. The result obtained from the fish caught shows that Monofilament gill net had a better performance than Multifilament gill net; this was attributed to the looseness and flexibility as well as the transparent nature of the net which makes it invisible in water. However, from the statistical analysis (variance test) carried out, there was no significant (P>0.05) difference in numbers and weight of fish species caught by the two nets

Growth performance of juvenile Clarias gariepinus fed Ipomoea aquatica based diets

A feeding trial was conducted to assess the replacement value of I. aquatica-based diet as dietary replacement of maize in the diets of C. gariepinus. Five isonitrogenous diets were formulated to contain 0% (control diet), 15% 30%, 45%, and 60% I. aquatica. Treatment was carried out in triplicate using ten C. gariepinus juvenile per replicate with mean initial weight of 9.0g. The fish at 5% body weight per day for a period of 8 weeks. The best growth response in terms of mean weight gain was obtained in 15% I. aquatica diet inclusion (35.57 ~c 3.44g), while fish fed 60% I. aquatica diet had the lowest growth response (23.80 ~c 1.18g), FCR was obtained in fish fed 60% I. aquatica (1.79 ~c 0.04), while the lowest was obtained in fish fed 15% I. aquatica. There was no significant difference (p>0.05) in all the parameters of the treatments. The results revealed that any of the inclusion level can be used up to 60% inclusion level of I. aquatica. However, 15% inclusion level gave the best result in terms of growth

Heavy metal content of sole, Solea solea and croaker, Pseudotolithus typus from Lagos and Delta State, Nigeria

This study investigated the levels of lead (Pb), cadmium (Cd), Copper (Cu), Chromium (Cr) and Zinc (Zn) in two common edible fish species, Sole, Solea solea and Croaker, Pseudotolithus typus from Makoko and Koko in Lagos and Delta states respectively. Heavy metal contents were determined by air-acetylene flame Atomic Absorption Spectrophotometer after wet digestion of dried and milled samples with 1:1 HN03: H2O2. Results obtained (~kg/g, dry weight) for Sole in Lagos and Delta states were: Pb (0.330 and 0.149), Cd (0.097 and 0.063), Cu (0.869 and 0.434), Cr (1.184 and 0.826), Zn (7.612 and 7.890); and Croaker: Pb (0.163 and 0.045), Cd (0.115 and 0.029), Cu (0.990 and 0.694), Cr (1.008 and 1.038) and Zn (6.756 and 6.168) for the wet season (April-October); and Pb (0.534 and 0.527), Cd (0.373 and 0.410), Cu (0.437 and 0.556), Cr (0.834 and 0.983), Zn (6.764 and 9.343) for sole and Pb (0.210 and 0.213), Cd (0.264 and 0.307), Cu (0.442 and 0.483), Cr (0.577 and 0.597) and Zn (4.783 and 5.924) for croaker in the wet season (July-October). Significant (P~B 0.05) variations were observed in metal content between fish in terms of species, location and season. Generally, sole had higher metal concentrations than croaker; and metal contents were higher in samples from Lagos compared to Delta, probably due to the contribution of more effluents from industrial, commercial and municipal wastes in Lagos state. Cd and Cr levels in the test species were found to exceed international standards. It is recommended that a programme of continuous monitoring and control of the physical and chemical characteristics of components and food products of Nigeria's coastal zone be incorporated as a management tool for this important ecological zone

Effects of diesel-oil spillage of fresh, brackish and marine waters on polyvinyl-alcohol (PVA) synthetic fishing twine

The effects of diesel-oil spillage of fresh (0.4ppt), brackish (25ppt) and marine (37ppt) waters on elongation (cm) and breaking load (kgf) of artisanal PVA synthetic twine of varied diameter (4mm, 6mm, 8mm and 10mm) soaked for 16 weeks was studied. Chemical (solubility) test was carried out to identify the experimental twine as PVA among other synthetic twines. The elongation (cm) and breaking load (kgt) of PVA twine diameters were tested by tensile-strength gauge machine (0-200kg) and was carried out in unpolluted (control) and polluted states (spillage level) at 0%, 20%, 40%, 60%, 80% and 100% diesel-oil concentrations of different water salinity. Factorial statistics was used to analyze the treatments; twine (at four levels), water salinity (at three levels) and concentrations (at six levels). This implies 4 by 3 by 6, replicated in four places (288 treatments). Results indicated that elongation (cm) and breaking load (kg) of the specimens were significantly (P<0.05) influenced by twine thickness. Twine l0mm soaked in 3.0 litres of unpolluted freshwater had significant (p<0.5) correlation coefficient r,0.927 and lowest r- value of 0.499 was obtained in twine 4mm soaked in 100% diesel-oil concentration. Significant (P <0.05) relationships were observed between the correlation coefficient r = 0.531-0.927 for unpolluted and r = 0.499-0.592 for polluted tests. The study revealed that diesel-oil spillage had negative effects on the quality of twines. The thicker the PVA twine diameters (10, 8, 6 and 4mm) at lowered (0%, 20%, 40%,60%,80% & 100%) diesel-oil spillage of fresh (0.4ppt), Brackish (25ppt) and Marine (37ppt) waters respectively, the higher the significant (P<0.05) elongation (cm) and breaking load (kgt) were evaluated in most cases

Fatty-acid composition of Macrobrachium vollenhovenii in Ogun estuary, Nigeria

A study was carried out on the fatty-acid composition of Macrobrachium vollenhovenii (African river prawn) in Ogun estuary, Ogun State, Nigeria. Sexes and size groups were considered during the study. Fatty-acid analysis was done in triplicates and data obtained were analyzed using descriptive statistics, analysis of variance and Duncan's multiple range tests. Fatty acids analysed which included oleic acid, linoleic acid,' stearic acid, myristic acid, palmitic acid and lauric acid were classified into saturated and monounsaturated fatty acids. All values of saturated fatty acids were higher in female (29.64%) than in male (25.50%) p< 0.05. So also the monounsaturated fatty acid also showed higher value in female (29.64%) than in male (25.50%). All fatty- acid values were higher in female M. vollenhovenii than in male. Meanwhile, myristic acid was highest in the two sexes and the combined sexes, (35.68% female), (33.14% male) and (34.74% combined sexes). The fatty-acid components were not influenced by the size of the fish. This study clearly indicated that the nutritive value of M. vollenhovenii is quite well comparable to the edible species of decapods already studied (shrimps, prawns and lobsters) and could be included in both human and livestock diets

Natural diets and length-weight relationship of Brycinus macrolepidotus in lower Ogun River, Akomoje, Ogun state

The natural diets and length-weight relationship of Brycinus macrolepidotus in Lower Ogun River, Nigeria was studied. 124 fish samples were collected twice monthly from February-August, 2015 from catches landed by artisanal fishermen using cast nets and long line. The total length and total body weight of all fish captured were measured and then grouped into sizes. Length-weight relationship was determined using the formular W = aLb. Gut contents were determined using the frequency of occurrence and numerical method. Index of fullness was also determined. Result of stomach content suggests omnivorous feed habit as diet were of plant and animal materials. Stomach fullness was higher during the dry season and onset of the rains than at the peak of the rains. Mean total length and weight of specimens varied from 18.19 ± 1.59 cm and 71.21 ± 15.54 g (juveniles), 34.99 ± 2.80 cm and 142.25 ±34.05 g (subadults) and 24.45 ± 2.53 cm and 301.46±22.67 g (adults) respectively. Length-weight analyses showed negative allometry for all sizes (b<3) and ‘r’ values 0.8252 to 0.9963. The study contributes to documented facts about the species from water bodies with a view of developing its aquaculture

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

Effects of Adansonia digitata (Baobab) bark meal additive on growth performance and nutrient utlization of Clarias gariepinus fingerlings

Feeding trial was carried out to determine effects of Adansonia digitata bark meal (ADBM)on growth performance and nutrient utilization of Clarias gariepinus fingerlings. Six iso-nitrogenous diets (40% crude protein) were formulated with ADBM at six levels (D1- D6)(0.00, 0.20, 0.40, 0.60, 0.80 and 1.00%). One hundred and eighty fingerlings (3.09 ± 0.21 g) were stocked at ten fingerlings per tank in 18 plastic tanks (58L). Each treatment was replicated in a completely randomized design and fish were fed to satiation for 12 weeks. Data was analyzed for analysis of variance and Duncan Multiple Range Test to separate means .A. digitata bark contained oxalate, alkaloid, tannin, flavonoid, saponin steroid, anthraquinone, terpenoid, glycoside and phenol. Growth and nutrient utilization indices showed significant differences (p&lt;0.05) among treatments. Mean weight gain (MWG) (41.77±1.88 g), final mean weight (FMW) (44.76±1.88 g), percentage weight gain (PWG) (1398.2±38.50%), daily growth weight (DGR) (0.50±0.02 g/day), apparent net protein utilization (ANPU) 76.73±3.98% and protein efficiency ratio (PER) 2.15±0.04 were highest in fish fed D3. MWG (31.27±2.48), FMW (34.31±2.25), PWG (1035.9±161.94%) and DGR (0.37±0.03) were lowest in fish fed D5. However, ANPU (49.84±4.23) and PER (1.45±0.07) were lowest in fish fed D6. Feed conversion ratio was best in fish fed D3 (1.17±0.29) while D6(1.72±0.08) was poorest.Keywords: Utilization, growth, fingerlings, Adansonia digitata bark, Clarias gariepinu

Gillnet selectivity of Sarotherodon galilaeus of Asejire lake, Oyo state, Nigeria

Gillnet selectivity is a management tool that is used to regulate the mesh size used for exploitation of fisheries resources in aquatic ecosystems. This is done to prevent overfishing of various types. Gillnet selectivity of Sarotherodon galilaeus of Asejire Lake is estimated in this study. Three mesh sizes 50.8 mm, 63.5 mm and 76.2 mm were found used predominantly in Asejire Lake. These mesh sizes caught various sizes of fish within the range of 11–24 cm. The optimum lengths for mesh sizes 50.8 mm, 63.5 mm and 76.2 mm were 15.09 cm, 18.86 cm and 22.63 cm respectively. Therefore, 63.5 mm mesh size is recommended as the appropriate mesh size for exploitation of S. galilaeus of Asejire Lake.Key Words: Gillnet, selectivity, mesh sizes, overfishing, Sarotherodon galilaeus, Asejire Lak

Some limnological characteristics of Asejire Lake, Asejire, Southwest Nigeria

Asejire Lake is one of the man-made lakes in the southwestern Nigeria. Physico-chemical characteristics of the lake were investigated for eleven months from January to December, 2014. Four sampling stations were established within the lake. Water samples were collected monthly from the four stations. Some limnological parameters were analyzed in-situ with analytical instruments while others were determined in the laboratory using standard laboratory methods. Descriptive and inferential statistics and principal component analysis (PCA) were employed for data analysis. Significant difference (p&lt;0.05) was observed in each month in all the measured parameters during the study period. Mean air temperature was 31.6±0.56˚C with no significant difference (p&gt;0.05) among stations. Highest value of alkalinity, hardness, nitrate and phosphate were recorded in July (107.5 mgCaCO3/L), May (167.5 mgCaCO3/L), May (6.9 mg/L) and October (0.52 mg/L), respectively. Electrical conductivity, total dissolved solids, pH, alkalinity, hardness and nitrate were significantly higher (p&lt;0.05) in the wet season than dry season. All the measured water quality parameters were within the recommended WHO standards for drinking water and aquatic life. Two components were identified by PCA; TDS (0.820) and phosphate (0.795). It can be concluded that the lake water is unpolluted and should be protected.Keywords: water quality, ecosystem, productivity, season, monitorin