There is a growing concern on the safety of frozen fish imported from various parts of the world where the levels of contamination of water bodies may not be well ascertained and regulatory measures not strictly adhered to. Concentrations of four heavy metals (Lead (Pb), Cadmium (Cd), Copper (Cu) and Mercury (Hg)) in the muscle, gill and liver were investigated for three most consumed frozen fish species (Umbrina canosai, Clupea harengu and Scomber scombrus) within Ibadan, metropolis. Samples were digested as described by FAO/SIDA. The concentrations of metals were quantified using a Varian AA240 Fast Sequential Flame Atomic Absorption Spectrophotometer (AAS). Heavy metals like Cd, Cu and Hg were significantly higher (p<0.05) in the liver of the three species than in the muscle and gills. There was no significant difference in the Pb concentration for the three organs in S. scombrus, whereas, Pb was significantly higher in the liver of U. canosai (9.73 mg kgG 1) and C. harengus (4.40 mg kgG 1) than in the muscle (6.92 and 2.11 mg kgG 1 , respectively) and gill (8.73 and 2.52 mg kgG 1 , respectively). Copper concentration was marginally higher in S. scombrus (5.06 mg kgG 1) with the least value recorded in U. canosai (3.28 mg kgG 1). However, no significant variation (p>0.05) was observed in the muscle Cd, Cu and Hg levels for the three species. Comparatively, S. scombrus has the highest concentration of heavy metals. This study revealed that the heavy metals investigated in the major organs and flesh was all above the limits recommended by World Health Organization.

Management of C. gariepinus fry in recirculating tank is one modern technique applied for fish culture in Nigeria. Since, this system is gaining popularity nationwide there is a dare need to investigate appropriate stocking density as already established for both concrete tanks and earthen pond system. Clarias gariepinus fry (0.14±0.01 g) were reared in indoor recirculating tanks (60.5 m 3 ) at three different stocking rates 5000, 8000 and 12000 fry/tank as treatment LD, MD and HD respectively for a period of eight weeks. The experiment was duplicated and fish were fed 45% crude protein diet at 5% in four installments daily. The mean body weight gain and SGR decreased with increasing stocking density. The best growth performance (weight gain, length gain and SGR) was achieved in treatment LD. The lowest FCR (1.04±0.01) value was obtained in HD but show no significant difference (p>0.05) to other treatments. Percentage survival of the fish was significantly (p<0.05) affected by the stocking density with the highest value recorded in LD (86.8%). Waterquality parameters were within the recommended ranges throughout the experimental period. From this study, the stocking density of 5000 fry mG 3 is recommended for efficient feed utilization, optimum growth performance and survival in a re-circulatory culture system.

Abstract:Egg adhesiveness has been a major problem affecting the hatchability of Clarias gariepinus. The removal of egg stickiness will improve aquaculture production through enhanced hatching rates. However, appropriate media for removal of adhesiveness in Catfish eggs is not yet well established. This study therefore, determine the optimum concentration and rinsing time of powdered milk (PM), Urea (UR) and Tannic acid (TA) for removal of adhesiveness of African catfish eggs and their effect on fertility and hatching success. Milt and eggs obtained from African Catfish broodstock of the same lineage were used for induced breeding following standard procedure. Four hundred fertilized eggs each were rinsed in the three different media at varying concentrations and exposure time using dry and wet fertilization methods. Treatment efficacy was assessed by comparing the percentage of non-stick eggs, fertilization, hatching and survival rate in the treatment groups and the control. Data were subjected to multivariate general linear model and Duncan multiple range tests at α 0 . 05 . Under the wet fertilization method eggs exposed to 10 g PM at 20 minutes gave the highest number of free eggs (87.50%) while 6g UR at 5 minutes recorded the lowest (27.09%). In dry method, 14 g PM at 20 minutes recorded the highest number of free eggs (90.00%) whereas, the lowest (47.50%) was recorded in 6g urea at one minute rinsing time. The highest number of hatchlings for PM, UR and TA were 53.26%, 33.24%, and 13.13%, respectively. The survival rate was high in all treatments except in 1.5 g TA. Eggs treated with PM solution performed best in adhesiveness removal and recorded highest percentage fertilization and hatching rate. However, more studies should be conducted to establish the appropriate media for other culture fish species.

African snakehead (Parachanna obscura) is a highly valued freshwater fish species in Nigeria, but its availability for economic and nutritional benefits is being threatened as a result of overdependence on wild source. Effort at bringing it to culture is, however, being limited by paucity of information on its biology among other challenges. Therefore, key aspects of the reproductive biology of this species were investigated as a prelude to artificially propagate it. 688 live samples comprise of 394 females (12.6-45.0cm TL) and 294 males (12.8-41.6cm TL) were fortnightly obtained in Eleyele Lake between November 2014 and October 2016 from fishermen majorly using longline, cast nets and gillnets of various mesh sizes. Morphometric parameters of fish were taken, and each sample dissected for sex identification following standard method. The maturation stages were analysed using macroscopic and standard histological techniques. The sex ratio of samples varied significantly (p< 0.05), with 1.34 females for every male. Five stages of oogenesis and three stages of spermatogenesis were obtained from samples analysed. Mean gonadosomatic index were significantly higher in May (2.26±0.86%), June (2.08±0.80%) and January (1.98±0.77%) for female samples and in June (0.18±0.06%) and December (0.21±0.06%) for male, implying peaks of gonadal development for the sexes. Length at first maturity calculated was 26.6 cm for males and 25.8 cm for females. The diameter of ova, however, varies from 0.60 to 1.42 mm. Absolute fecundity ranged between 336 (at 20.5cm total length) and 7,033 (at 36.7 cm total length). The relationship between fecundity and total length, weight, ovary length and ovary weight was linear and positive. This research provides key information necessary for artificial propagation of P. obscura.

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