Effect of Different Fertilization and Egg De-adhesion Methods on Hatching and Survival of Clarias gariepinus (Burchell 1822) Fry

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. Journal of FisheriesSciences.com Kareem et al., 11(1): 021-027 (2017) adhesiveness of fishes, includes: milk for common carp, Cyprinus carpio (El-Gamal et al., 2008), tannic acid for pikerpich, Sander lucioperca (Demska et al., 2005), kaolin for shishamo smelt, Spirinchus lanceolatus (Mizuno et al., 2004), mud solution in Japanese dace, Tribolodon hakonensis (Nakamura, 1966) and urea solution in carp (Rothbard, 1978). To date, few studies have been done on how best to remove adhesiveness of the African catfish eggs in Nigeria despite dominating local fish production. Therefore, this study is carried out to find the best solution required to eliminate the stickiness of the African catfish eggs for improve fertilization and hatching rates. Herein, powdered milk, urea solution and tannic acid at different concentrations were evaluated. Materials and Methods The experiment was conducted in 72 plastic aquaria of sizes 0.39 m×0.27 m×0.26 m at the Wet Laboratory, Department of Aquaculture and Fisheries management, University of Ibadan from May to July, 2015. A male and a female broodstock of African catfish weighing 700-1200 grams were obtained from a commercial farm in Ibadan and acclimatized in separated tanks for 24 hours. The female brooder was artificially induced following Olanrewaju et al. (2009). Twelve hours after injection, the milt was collected from the male broodstock by sacrificing the male broodstock. This is necessary as catfish milt cannot be released by abdominal pressing (Muchlisin et al., 2014). Gentle pressure was applied on the abdomen of the female brooder and the ovulated eggs that were ooze out easily from the genital opening was collected in a clean dry plastic bowl (Nwachi et al., 2014). For all the treatments, both wet and dry methods of fertilization were used. For the dry method, the milt and eggs were mixed with plastic spoon and two drops of saline water added to activate the milt. For wet method, Milt was mixed with the saline solution in a flat bowl, poured onto the eggs and stirred gently with a plastic spoon to fertilize the eggs (Lawson and Ishola, 2003). For both methods, fertilized eggs were left for five minutes to allow the eggs make sufficient contact with the sperm. Three different concentrations of rinsing agents (powdered milk, Urea and Tannic acid) were prepared by dissolving appropriate quantity of solute in a liter of water and adding 1 gram and 4 grams sodium chloride respectively. Tannic acid solution was also prepared in the same way but without sodium chloride. 400 eggs were randomly counted and rinsed thoroughly in each concentration of urea, tannic acid and powdered milk and observed under different exposure time (Table 1). Each of the mixture was rinsed with water prior to transfer of eggs into the 20 L plastic container at room temperature. Flow-through water exchange method was used during incubation. The fertilized eggs from each of the treatments were spread on 30 cm×20 cm strips of mosquito netting. Incubation was monitored for 24 h with gentle water flow through. Egg adhesiveness was assessed by rating the percentage of clumping eggs. The number of completely free (non-stickiness) eggs and aggregated eggs in each container were counted after 15 minutes of incubation. The percentage of non-stickiness is estimated as follows: