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

Kareem OK1*, Ajani EK1, Akintunde MA2, Olanrewaju AN3 and Oduntan OB1

1Department of Aquaculture and Fisheries Management, University of Ibadan, Nigeria

2National University of Lesotho, Roma 120, Kingdom of Lesotho

3Federal College of Freshwater Fisheries Technology, P.M.B 1060, Maiduguri, Nigeria

Corresponding Author:
Kareem OK
Department of Aquaculture and Fisheries Management
University of Ibadan, Nigeria
Tel: +234 803 360 4468
E-mail: [email protected]

Received Date: 22.07.2016; Accepted Date: 29.09.2016; Published Date: 05.10.2016

 
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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 α0.05. 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 6 g 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.

Keywords

Powdered milk; Urea; Tannic acid; Stickiness; Catfish

Introduction

Aquaculture is one of the fastest growing food production systems in the world with developing countries contributing significantly to its growth (Haruna, 2003). It is acknowledge as the efficient means of providing food rich in protein, income and employment opportunities for the populace. FDF (2005) estimated potential of Nigeria in aquaculture as 1.3 million metric tonnes but its current contributions stood at 278,706 metric tonnes (FDF, 2015). With stagnating yields from many capture fisheries and increasing demand for fish and fishery products, there is high expectation for aquaculture to increase its contribution to the world’s aquatic food production. It is also hoped that aquaculture will continue to strengthen its role in contributing to food security and poverty alleviation in many developing countries (FAO, 2010). The culture of clariid catfish dominated local fish production in Nigeria and has grown rapidly since 1985 till now because it grows fast and feeds on a large variety of food, tolerate a wide range of water quality conditions, relatively easy to reproduce in captivity and can be raised in high density resulting in high yield (Okechi, 2004). Ojutiku (2008) noted that the scarcity of fingerlings of this widely acceptable species constitute a major constraint to the rapid development of fish farming in Nigeria. Charo and Orirere (2000) equally submitted that the major constraint to intensification and expansion of fish culture in Nigeria lies in inadequate supply of quality fingerlings and juveniles for stocking of ponds cages and pens. Atanda (2006) stressed that fish farmers in most part of the country (especially the Northern part) are perpetually in need of hatchery produced fish seed for their farm which is mostly not available. Documented evidences indicated that the total seed production and supply in Nigeria from all sources amount to 55 million fingerling while the immediate needs of the market is 500 million per annum (Atanda, 2007). Catfish larva production impediment is traceable to low hatching and survival rates (Muchlisin et al., 2010) which could be linked to the adhesiveness of eggs. The clump together of egg when they are released into the water results in low fertilization and hatching rates (El-Gamal and El-Greisy, 2008). In addition, adhesiveness of eggs can cause high larval mortality (Abigail et al., 2010). In African catfish, eggs are covered with a layer of mucus that gives them adhesiveness. Under natural condition, egg adhesiveness is a reproductive strategy of most teleost for protecting the eggs from water drifting. In the wild, African catfish spawning takes place at night in shallow water with temperatures above 22ºC and the eggs stick to the leaves and stems of vegetation (Little et al., 1994). However, in artificial spawning, the adhesiveness of the eggs could reduce fertilization and hatching rates. This is because the adhesiveness covers the microphiles and hinders the sperms from fertilizing the eggs (Prinsloo et al., 1987); the chances of sperm getting in contact with the eggs are reduced and hence the chances of the eggs getting fertilized are compromised. Also, when the eggs come into contact with water during the incubation period, it becomes clumped and this reduces the chance of the eggs to hatch. However, various techniques have been adopted to control reproduction in cultured fish species with the aim of achieving high fertilization of eggs and hence production of large number of fingerlings (Delinc et al., 1987). Materials in use to remove egg 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.

Rinsing agents Rinsing time (minutes)
Powdered milk Treatments (PM)  
0 g+1gNacl/L of water (Control)  
10 g powdered milk+1gNacl/L of water 15.0, 20.0, 25.0
12 g+1gNacl/L of water  
14g +1gNacl/L of water  
Urea Treatments (UR)  
0 g+4 g NaCl/L water(Control)  
2 g urea+4 g NaCl/L water  
4 g urea+4 g NaCl/L water 1.0, 5.0, 10.0
6 g urea+4 g NaCl/L water  
Tannic Acid Treatments (TA)  
0g Tannic acid/L of water  
0.5g Tannic acid/L of water  
1g Tannic acid/L of water 0.5, 2.0, 5.0
1.5g Tannic acid/L of water  

Table 1: Concentrations and rinsing time of different rising agents for removing egg adhesiveness. Demska-Zakes et al. (2005), Muchlisin et al. (2010), Amirul et al. (2013).

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:

image

Fertilization was evaluated after 30 minutes of incubation by counting the transparent embryos in relative to the white colour unfertilized or dead eggs. The percentage fertilization was calculated thus:

image

Hatching rates were observed after 24 hours of incubation, by counting the number of larvae produced. The hatchability percentage was estimated as follows:

image

The survival rate of larva was monitored for seven days for each treatment. The percentage survival rate was estimated as follows:

image

Water quality parameters were monitored during the experiment. Temperature, pH and Dissolved oxygen was determined daily using mercury-in-glass thermometer, pH meter (Hanna, model H198107) and dissolved oxygen meter (Labtech, model AVI-660), respectively. The raw data were tested by multivariate general linear model using SPSS (version 17) to examine the main effect of milk, Urea and tannic acid concentrations and interactions at different times on free, fertilized and hatching and survival rates. Duncan’s multiple range tests were used to determine differences among treatments.

Results

The Percentages of Non-stick eggs, fertilization, hatching and survival rate based on rinsing agents and interaction effects between rinsing agents and rinsing time is shown in Table 2. The interaction between the rinsing concentration and rinsing time for wet method of fertilization revealed that 10 g and 14 g PM gave the highest quantity of non-stick eggs (90.00% each) at 15 and 25 minutes, this was significantly different from other treatments (p<0.05). The results obtained in the control ranges from 43.75% at 25 minutes rinsing time to 61.25% at 20 minutes rinsing time. The fertilization rate was higher in 10 g PM at 15 minutes (95.75%) and this was significantly different from other treatment (p<0.05). The highest hatching of 62.50% was obtained from 10 g PM at 25 minutes exposure time. The control (0 g PM) gave the lowest hatching of 31.81% at 25 minutes rinsing time. The result from PM treatment gave high survival rate of between 91.67% and 100%. PM treatment using the dry method revealed that, 14g PM had the highest de-sticking ability (90.00%) at 20 minutes exposure time while the lowest was the control (31.67%) at 15 minutes rinsing time. The fertilization rate was higher in 12 g PM (97.50%) at 20 minutes; this was significantly different (p<0.05) from other treatment except 14 g PM at 25 minutes exposure time (92.09%). The lowest fertilization was recorded in the control with 15 minutes rinsing time. The result of hatchability indicated that, 10g PM at 20 minutes rinsing time gave the highest (72.66%), this was significantly different from other treatment (p<0.05). The result obtained implied high survival rate of between 94.00% and 100.00%.

Rinsing agent Rinsing
Time (mins)
Fertilization
Methods
Non
Stickiness (%)
Fertilization
(%)
Hatchability
(%)
Survival rate (%)
0 g PM/L of water 15.0 Wet 50.00  ±  0.00abc 76.25 ± 5.30bcd 34.29 ± 12.45ab 94.60 ± 4.49abc
  Dry 43.34  ±  2.35ab 49.17 ± 12.96a 51.67 ± 20.82abcd 100.00 ± 0.00c
20.0 Wet 61.25 ± 1.77bcde 73.75 ± 1.77bcd 34.80 ± 8.84ab 96.78 ± 1.73abc
  Dry 43.75 ± 8.84ab 70.00 ± 21.21abcd 41.71 ± 17.31abc 98.89 ± 1.56bc
25.0 Wet 43.75 ± 8.84ab 62.50 ± 15.38ab 31.81 ± 6.52a 100.00 ± 0.00c
  Dry 31.67 ± 2.35a 75.67 ± 23.81bcd 34.78 ± 17.66ab 98.00 ± 2.82bc
10 g PM/L of water 15.0 Wet 90.00 ± 7.07e 95.75 ± 4.59e 50.25 ± 0.35abcd 99.50 ± 0.71bc
  Dry 86.25 ± 5.30ef 93.13 ± 0.88cd 62.50 ± 17.68abcd 94.17 ± 5.89ab
20.0 Wet 87.50 ± 3.50ef 70.00 ± 7.07abc 50.70 ± 14.57abcd 100.00 ± 0.00c
  Dry 83.75 ± 1.77ef 92.50 ± 0.00cd 72.66 ± 24.98d 97.11 ± 1.06bc
25.0 Wet 83.67 ± 5.42ef 78.75 ± 5.30bcd 62.50 ± 17.68cd 96.89 ± 15.55abc
  Dry 73.75 ± 1.77cdef 78.75 ± 1.77bcd 47.50 ± 3.54abcd 98.00 ± 0.00bc
12 g PM/L of water 15.0 Wet 75.00 ± 21.21cdef 68.75 ± 5.30abc 37.00 ± 2.12abc 100.00 ± 0.00c
  Dry 77.50 ± 10.61def 85.00 ± 14.14bcd 51.68 ± 15.81abcd 99.55 ± 0.0.64bc
20.0 Wet 81.25 ± 22.90de 78.75 ± 8.77bcd 53.35 ± 18.89abcd 91.67 ± 2.35a
  Dry 88.75 ± 8.83e 97.50 ± 4.33e 57.82 ± 11.05abcd 98.52 ± 0.74bc
25.0 Wet 71.67 ± 11.79cdef 86.26 ± 10.4bcd 61.95 ± 21.14abcd 99.50 ± 0.71bc
  Dry 52.50 ± 3.54abcd 81.25 ± 15.91de 40.23 ± 14.83abcd 98.75 ± 2.17bc
14 g PM/L of water 15.0 Wet 75.00 ± 21.21cdef 91.25 ± 1.77cd 44.70 ± 0.42abcd 97.50 ± 3.54bc
  Dry 80.00 ± 3.54ef 91.25 ± 1.77cd 48.34 ± 25.93abcd 96.21 ± 4.07abc
20.0 Wet 72.50 ± 28.28cdef 86.25 ± 15.90def 41.00 ± 15.56abc 98.34 ± 2.35bc
  Dry 90.00 ± 3.54e 95.00 ± 0.00def 56.61 ± 28.72abcd 97.84 ± 1.65bc
25.0 Wet 90.00 ± 3.54e 81.25 ± 15.91de 65.70 ± 8.06bcd 99.50 ± 0.71bc
  Dry 82.92 ± 0.59ef 92.09 ± 0.59e 60.05 ± 16.09abcd 94.00 ± 2.82ab

Table 2: Percentages of Non-stick eggs, fertilization and hatching and survival rate based on interaction effects between rinsing agent (powdered milk) and rinsing time.

Table 3 showed the effects of UR treatments on the Stickiness removal, fertilization and hatching rates (P<0.05). For wet method of fertilization, the non-sticky rate varied from 38.75% to 69.20% in control (0 g UR) at 10 minutes rinsing time and in 6 g UR also at 10 minutes rinsing time, respectively. The fertilization rate ranged from 34.17% to 97.86% in 6 g UR at 5 minutes rinse time and in 2 g UR with 10 minutes rinsing time, respectively. In addition, the hatchability result ranges from 16.15% to 40.24% in 4 g UR at 10 minutes rinsing time and in 2 g UR at 10 minutes rinsing time. Survival rate ranges from 81.25% to 100.00% in 6 g urea at 10 and 5 minutes exposure time respectively. Among the treatments, the concentration of 6 g urea at 10 minutes rinsing time gave the best results for removing stickiness of eggs (69.20%), this was significantly different from other treatments (p<0.05). On the other hand, the 2 g UR at 10 minutes rinse time recorded the highest fertilization (97.86%), which was significantly different (p<0.05) from other treatments. In addition, the same concentration of UR gave the highest numbers of hatchlings (40.24%), but this was lower than the control at 1 minute rinsing time (47.75%). However, these results were not significantly different from other treatments (p>0.05). The results obtained from survival rates indicated high percentage survival rates in all the treatments. On the effect of rinsing agent on stickiness removal under dry method of fertilization, 4 g urea gave the highest percentage of free eggs, (60.42%) at 5 minutes rinsing time. However, this was not significantly different from other treatments. The same concentration of 4 g urea at 5 minutes rinsing time had the highest fertilization (91.84%), and hatching rate (51.59%). The result of fertilization indicated a significant different among treatments, while for hatchability, there was no significant difference among the treatments. In addition, high survival rates were recorded in all the treatments.

Rinsing agent Rinsing
Time (mins)
Fertilization
Methods
Non
Stickiness (%)
Fertilization
(%)
Hatchability
(%)
Survival rate (%)
0 g UR/L of water 1.0 Wet 41.84 ± 0.23ab 73.83 ± 15.80ab 47.75 ± 3.18a 98.18 ± 0.25a
  Dry 51.67 ± 9.42ab 52.50 ± 3.54ab 40.77 ± 6.39a 96.66 ± 4.72a
5.0 Wet 42.30 ± 10.32ab 62.50 ± 17.68bcde 34.63 ± 1.24a 99.17 ± 1.18a
  Dry 47.91 ± 2.95ab 55.67 ± 3.77abc 34.15 ± 4.09a 93.65 ± 7.98a
10.0 Wet 38.75 ± 5.30ab 53.75 ± 5.30ab 39.25 ± 4.24a 98.46 ± 0.52a
  Dry 40.00 ± 14.14ab 52.09 ± 7.66ab 33.50 ± 4.95a 100.00 ± 0.00a
2 g UR/L of water 1.0 Wet 42.50 ± 19.70ab 94.14 ± 0.19de 39.03 ± 29.66a 97.50 ± 3.54a
  Dry 45.50 ± 7.07ab 67.71 ± 16.21abcd 45.45 ± 0.00a 98.33 ± 0.00a
5.0 Wet 53.64 ± 15.05ab 69.70 ± 33.76abcd 31.11 ± 33.79a 99.09 ± 1.29
  Dry 60.42 ± 17.09ab 79.59 ± 0.59abcd 29.54 ± 14.79a 97.75 ± 0.35a
10.0 Wet 48.81 ± 21.88ab 97.86 ± 0.00e 40.24 ± 49.17a 99.34 ± 0.94a
  Dry 50.42 ± 6.48ab 72.50 ± 31.82bcde 36.19 ± 40.75a 92.09 ± 9.02a
4 g UR/L of water 1.0 Wet 50.42 ± 24.12ab 64.05 ± 11.95abcd 26.79 ± 32.81a 100.00 ± 0.00a
  Dry 54.33 ± 22.15ab 84.25 ± 13.79bcde 51.59 ± 2.26a 97.34 ± 3.77a
5.0 Wet 61.46 ± 27.99ab 69.58 ± 20.04abcd 33.77 ± 44.17a 96.93 ± 4.35a
  Dry 48.50 ± 12.02ab 91.84 ± 9.67cde 35.07 ± 35.26a 95.83 ± 3.54a
10.0 Wet 53.13 ± 4.42ab 56.40 ± 2.26abc 16.15 ± 12.52a 100.00 ± 0.00a
  Dry 49.45 ± 14.92ab 81.52 ± 25.13bcde 21.79 ± 25.75a 98.75 ± 1.77a
6 g UR/L of water 1.0 Wet 37.50 ± 24.75ab 58.25 ± 6.01abcd 32.20 ± 17.25a 99.17 ± 1.18a
  Dry 47.50 ± 8.89ab 62.78 ± 4.59abcde 20.70 ± 25.37a 87.55 ± 7.32a
5.0 Wet 27.09 ± 2.94a 34.17 ± 12.96a 27.50 ± 10.61a 100.00 ± 0.00a
  Dry 49.84 ± 11.55ab 76.88 ± 23.86bcde 32.72 ± 38.59a 89.96 ± 11.84a
10.0 Wet 69.20 ± 18.31b 68.93 ± 1.66abcde 18.65 ± 16.05a 81.25 ± 26.52a
  Dry 50.62 ± 7.95ab 60.00 ± 14.14abcd 23.70 ± 23.05a 91.99 ± 7.78a

Table 3: Effect of Urea as anti-sticking agent on fertilization, hatchability of Clarias gariepinus eggs and survival of the hatchlings.

On the effect of TA treatment on stickiness removal, fertilization, hatching and survival rate, it could be deduced that TA had significant effect on stickiness removal. For wet method of fertilization, treatment with 1.5 g TA at 0.5 minute exposure time recorded the highest numbers of free eggs (96.17%) while for dry method; 0.5 g at 5 minutes exposure time recorded the highest number of free eggs (85.84%). These were significantly different from other treatments. The fertilization rate showed that, wet method with 1.5 g TA at 2 minutes exposure time gave the highest fertilization rate (97.19%), which was significantly different (p<0.05) from other treatments (Table 4).

Rinsing agent Rinsing
Time (mins)
Fertilization
Methods
Non
Stickiness (%)
Fertilization
(%)
Hatchability
(%)
Survival rate (%)
0 g TA/L of water 0.5 Wet 41.32 ± 3.44ab 50.75 ± 1.77a 41.50 ± 5.66b 100.00 ± 0.00c
  Dry 40.63 ± 4.42ab 58.50 ± 1.41abc 51.25 ± 2.47c 98.90 ± 1.56c
2.0 Wet 29.86 ± 10.80a 57.75 ± 0.35abc 38.00 ± 6.01b 93.26 ± 1.99bc
  Dry 42.08 ± 1.77abc 56.25 ± 1.77abc 49.50 ± 0.71c 99.21 ± 1.12c
5.0 Wet 48.13 ± 0.88abcd 53.88 ± 1.59ab 41.00 ± 5.66b 96.19 ± 2.26bc
  Dry 43.75 ± 8.83abc 59.95 ± 1.70abc 49.38 ± 4.41c 97.30 ± 3.82c
0.5 g TA/L of water 0.5 Wet 49.17 ± 1.81abcd 52.71 ± 2.06abc 4.13 ± 1.24a 87.50 ± 17.68bc
  Dry 65.10 ± 13.49abcdef 96.22 ± 0.30cd 2.25 ± 0.35a 100.00 ± 0.00c
2.0 Wet 53.13 ± 4.42abcd 53.13 ± 8.83a 1.25 ± 0.0.00a 66.67 ± 23.57bc
  Dry 81.72 ± 19.57cdef 81.04 ± 23.68abc 3.38 ± 0.53a 83.07 ± 23.19bc
5.0 Wet 71.78 ± 35.21bcdef 65.97 ± 40.26abc 1.00 ± 0.00a 50.00 ± 70.71abc
  Dry 85.84 ± 15.32def 96.33 ± 2.67cd 1.13 ± 0.66a 100.00 ± 0.00abc
1 g TA/L of water 0.5 Wet 91.67 ± 7.07ef 71.34 ± 34.88abc 3.13 ± 0.18a 70.84 ± 5.89bc
  Dry 77.60 ± 21.46bcdef 83.42 ± 17.79abc 2.88 ± 0.53a 99.60 ± 0.37bc
2.0 Wet 77.91 ± 21.80bcdef 73.94 ± 31.80abc 0.88 ± 0.18a 75.00 ± 35.36bc
  Dry 80.90 ± 16.80bcdef 85.27 ± 16.29abc 1.13 ± 0.17a 99.60 ± 0.57c
5.0 Wet 82.27 ± 19.11cdef 82.61 ± 15.17abc 0.50 ± 0.00a 50.00 ± 70.71abc
  Dry 80.89 ± 15.40bcdef 81.03 ± 11.17abc 0.50 ± 0.00a 100.00 ± 0.00abc
1.5 g TA/L of water 0.5 Wet 96.17 ± 0.86e 93.05 ± 2.75abc 0.82 ± 0.26a 50.00 ± 70.71abc
  Dry 69.38 ± 25.63abcdef 74.65 ± 24.25abc 0.50 ± 0.00a 66.67 ± 57.74abc
2.0 Wet 87.07 ± 12.01def 97.19 ± 2.31c 0.50 ± 0.50a 25.00 ± 43.30abc
  Dry 80.63 ± 16.79bcdef 85.59 ± 12.31abc 1.50 ± 0.00a 49.00 ± 69.30abc
5.0 Wet 85.39 ± 14.69def 82.61 ± 15.17abc 1.25 ± 1.06a 50.00 ± 70.71a
  Dry 68.24 ± 24.28abcdef 67.93 ± 24.44abc 0.50 ± 0.50a 25.00 ± 43.30ab

Table 4: Percentage of non-stickiness, fertilization, hatchability and survival of Clarias gariepinus eggs exposed to varying rinsing time and concentrations of Tannic acid solution.

The results obtained for stickiness removal using dry method showed that, 0.5 g at 5 minutes rinsing time achieved the highest (96.33%) result, which was not significantly different for the same concentration at 2 minutes exposure time (p<0.05). As regard the effect of TA on hatching rate, there were no significant difference among the treatments (p>0.05), except for the control. Generally, low hatching rate was recorded in the treatments with tannic acid. The highest number of hatchlings obtained was at 0.5 minute exposure time for wet (41.50%) and dry (51.25%) methods respectively. Treatment with 1.5 g TA recorded the lowest survival rates.

Discussion

The powdered milk proved to be the most appropriate media for the removal of egg adhesiveness when compared with tannic acid and urea. This may be due to the inherent ability of milk to reduce the rate of egg aggregation by coating it with the milk particles. The coating prevents the eggs from sticking to each other. This in-turn increased fertilization rate as the sperm can have a direct contact with the eggs without the obstacle of the mucus layer on the egg surface. The hatching rate also increased in the treatment with powdered milk solution when compared with the control. The high survival rate observed under this treatment indicated that, at this optimum concentration the rinsing agent concentration do not have any negative effect on the survival of hatchlings. Mohammed et al. (2015) reported that introduction of rinsing agent makes the eggs discrete and non-sticky after treatment which invariably allowed easy spread of eggs in the incubator and hence facilitate easy separation of hatchlings from egg cases. Kudo (1982) submitted that the cortical envelope of fish egg is rich in protein and acid phosphates which are responsible for stickiness of eggs when in contact with water. Elimination of stickiness is therefore, critical to reduce adhesive effect, increase embryonic development, hatching and easy management of the incubator. The use of powdered milk solution for the removal of stickiness of Clarias gariepinus eggs showed that the optimum concentration and rinsing time under wet method of fertilization was 10 g powdered milk at 20 minutes rinsing time while the best concentration of rinsing agent and rinsing time recorded for dry method of fertilization was 14 g powdered milk at 20 minutes rinsing time. This was in accordance with the findings of Muchlisin et al. (2014) who reported optimum concentration of 14 g powdered milk/L solution at 25 minutes rinsing time for African catfish eggs under dry fertilization method. It could however, be seen from the result of this experiment that, the concentration of 14 g powdered milk recorded the highest fertilization rate for both dry and wet method of fertilization, but at different rinsing time of 15 minutes (wet) and 20 minutes (dry) respectively. This agreed with the findings of Muchlisin et al. (2014), who recorded higher fertilization rate in 12 g powdered milk. Generally, there was high survival in both the treatment with powdered milk solution and the control.

The use of powdered milk as organic dissolvent to remove egg stickiness has been reported by Soin (1976). However, Linhart et al. (2003) reported the use of enzymes. According to Palikoval and Krejci (2011), a combination of whole milk and talc result in 80%-90% anti stickiness and hatching rate while whole milk only gave 70% results. This confirmed that urea has positive effect on removal of egg adhesiveness. From this experiment, 4 g urea at 10 minutes rinsing time was the optimum concentration and rinsing time for removing the stickiness of eggs in African catfish under wet method of fertilization while 2 g urea at 5 minutes rinsing recorded the highest numbers of free eggs in dry method. El- Gamal et al. (2008) examined the removal of egg adhesiveness in Common carp (Cyprinus carpio) using a mixture of 3-5 gm of urea and 4 gm of NaCl/L of water. The authors however, obtained the best result in 4 gm urea/L of water. According to Woynarovich and Woynarovich (1962) and Rothbard (1978), the function of urea in adhesiveness removal is to remove glutinosity of egg. However at higher concentrations, the urea may cause the basal membrane of the egg to be overly and disturb the chorion development resulting in lower fertilization and hatching rates as corroborated by Amirul et al. 2013. Overall, the number of free eggs, fertilization and hatching rates recorded in this study were higher than that of Amirul et al. 2013. The post hock test showed that tannic acid concentration had significant effect in removing the adhesiveness of African catfish eggs, but the rinsing time and interaction between rinsing agent and rinsing time does not indicate any significant effects. This contradict the report of Demska et al. (2005) which submitted that, both the concentration of tannic acid and exposure time significantly impacted the degree of stickiness removal and embryo survival. Ozdal et al. (2013) adduced variability in result when using tannic acid to different in water quality parameters which plays a significant role in the reaction between phenol groups and proteins. The result revealed that concentration of tannic acid of between 1 g to 1.5 g at 2-5 minutes exposure time was the best in removing the stickiness of African catfish eggs for both method of fertilization. This is similar to the result of Demska-Zakes et al. (2005) who reported that the adhesiveness of pike perch eggs disappeared completely at 5 minutes exposure to tannic acid solution of 0.5-1.5 g L-1. The authors further submitted that, the tannic acid solution of ≤0.5 g L-1 applied at 0.5-2 minutes was not effective; the eggs clumped and it was impossible to separate them even with intensive mixing while better results were obtained using higher tannic acid concentrations and/or by lengthening exposure time. Treatment with 1.5 g produced the highest fertilization rate under wet method of fertilization while 5 g was recorded as best for dry. For hatching, the result indicated that Tannic acid has a negative effect on African Catfish eggs as the highest hatching recorded for wet and dry method were 2.13% and 2.25% respectively, notwithstanding its significant effect on removing egg stickiness. Similar observation was reported by Demska-Zakęś et al. (2005) when tannic acid was used on the pikeperch, Sander lucio percaeggs. At high concentration, tannic caused the chorion to harden, thus decreasing the chorionase activity. Also, Amirul et al. (2013) reported that higher concentrations of urea may cause the basal membrane of the egg to be overly abraded and disturb the chorion development resulting in lower fertilization and hatching rates. From this study, 0.5 g tannic acid gave the highest hatching rate. This implies that concentration of 0.5 g tannic and below will be the appropriate concentration for better hatching rate. This is supported by Demska-Zakes et al. (2005) who opined that high tannic acid concentration had a negative impact on the pikeperch larvae hatching.

Conclusion

This study shows that powdered milk, urea and tannic acid solution have significant effect on removing stickiness associated with Clarias gariepinus eggs. 10 g powdered milk at 20 minutes rinsing time remove adhesiveness in African catfish eggs better than all the other treatments. However, 14 g powdered milk at 15 minutes rinsing time proof to be the best concentration when fertilization and hatching rate are considered. The dry method of fertilization gave the best fertilization and hatching rate for the three media when compare with the wet method. There was high survival rate in all the treatments except for the treatment with 1.5 g tannic acid. The results therefore confirm that catfish eggs rinsed in powdered milk can reduce the clumping of eggs and also enhance fertilization and hatching rate.

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