Comparative assessment of hatching rates of African Catfish (Clarias gariepinus) eggs using Nile cabbage and Kaka Bans substrates

Jane M Gikonyo, Felix M Kibegwa and Benson O Inyangala

Department of Animal Production, University of Nairobi, PO Box 29053-00625, Nairobi, Kenya
gigsjane@gmail.com

Abstract

The dilemma, on which substrates are most suited for incubation of catfish fry, faces most hatchery managers. The hatchery managers also face an uphill task in ensuring that the ambient conditions required for incubation of catfish eggs are in place. The commonly and locally used substrates are Kaka bans (artificial) and Nile cabbages (Pistia stratiotes) (natural). This study was meant to compare hatching rates between these commonly used substrates and to establish if the difference is significant. The study was carried out at Sagana Fish Culture Farm where there is a modern hatchery, and both substrates are readily available. Three treatments; KB1: Kaka bans, NC2: Nile cabbages and TI3: Tray incubator (control experiment), were used.

Nile Cabbage ranked best in performance with a mean hatching rate of 267; trays were second with a mean rate of 115, while kaka ban mats were last with an average of 65. There were minimal costs incurred in the use of all three substrates in this experiment.

Key Words: catfish farming, fish eggs, Kenya

Introduction

The Clariasgariepinus species, market demand, has risen over the years. This escalating demand is not only for stocking of ponds but also its use as bait fish in capture fisheries (Munguti et al 2014). Since the 1970's, the species has been considered to hold great promise for fish farming not only in Kenya but Africa as a whole (Brummett et al 2008). This demand has been widely attributed not only to their ability to tolerate a broad range of environmental parameters but also their high reproductive potential and rapid growth (Clay, 1977; Hecht and Appelbaum 1988; Hogendoorn, 1980).Due to the unreliable nature of seed collection from wild and its limitation to the rainy season, hatchery seed production has opted. Other advantages of hatchery means of seed production are the elimination of the cannibalism phenomena of catfish and mass production to sustain the steadily growing demand, has been made possible.

Though high mortality of these eggs persists, in Kenya lower rates ranging from as low as 25% (Obuya et al 1995), have been recorded which were far much below the 50-70 % recorded in well-managed hatcheries in other countries (De Graaf et al 1995). Numerous studies have been carried out to increase hatching rates from improvement in aeration techniques to enhancement of water circulation throughout the individual eggs in the masses. Artificial incubation and hatching of catfish eggs in hatcheries was designed to simulate the natural environment where eggs are attached to plants and rocks while the parent(s) provide a constant water flow by fanning their fins. Additionally, the hatchery practice will increase the economic efficiency of a commercial fish culture operation (Watson and Chapman 2002).The aim of this experiment was to establish which of the two simple, locally available and low-cost substrates, Kaka bans (artificial) and Nile cabbages (natural), results in better hatching rates when ambient conditions are constant.

Materials and methods

This study was carried out at Sagana Fish Culture Farm, Kirinyaga County which is the National Center for Aquaculture in Kenya. The experiment was a conducted as a random block arrangement of three treatments (incubation substrates; KB1: Kaka bans (artificial substrate), NC2: Nile cabbage (natural substrate) and TI3 Tray-type of incubator (control), with two replications (Figure 1). The tray was used as a control since it freely allows water through it flushing out wastes and provide easy access for removal of dead embryos. The three substrates were thoroughly washed, disinfected and rinsed along with all the equipment before use. Further, 5 grams of common salt was added to the treatments (aquaria tanks) before incubation to prevent egg infections (Kubitza, 2016) (Figure 2).

Figure 1. Incubator substrates: a shows the kaka bans, b shows nile cabbages while c is the tray-type of

Figure 2. Aquaria tanks that were used as part of the incubation apparatus

Four randomly selected, ready to spawn, mature brood stock (ratio of 1:1) were first selected from brood stock ponds and transferred to the hatchery. Their weights were measured and recorded: females weighed 589g and 432g respectively while the males weighed >200g. The fish then underwent an acclimatization period for a day without feeding. 0.2ml per a kg of fish of Ovaprim®, a synthetic gonadotropin hormone, was injected intramuscularly into the dorsal muscleof all the females. Before being injected, the Ovaprim® was mixed with a physiological solution (9 grams of de-iodized salt dissolved in a liter of distilled water). After 12 hours, the females were stripped off ripe eggs while milt was obtained by sacrificing the males. The milt was diluted with the physiological solution before being added to the stripped eggs. An equal volume of clean water was then added to activate the sperms (De Graaf et al 1995).

Number of eggs in 0.01gram of eggs were counted under a microscope then used to calculate the weight equivalent to 500 eggs. The fertilized eggs were spread evenly on the substrates in bunches of 500 eggs per substrate.Throughout the experiment period, the Water temperature was maintained at 28.0 ± 1°C, Dissolved Oxygen (DO) at 6.0 ± 0.3 Mgl^-1, pH at 7.9 ± 0.4 and conductivity at 236 ± 15 µs. Hatching rate was obtained by a formula suggested by Viveen et al (1985)

After a latency period of 22 hours, the substrates were removed to obtain the hatchlings (De Graaf and Janssen 1996). Frame wood of the tray was shaken carefully to remove the larvae’s blocked by shells or mesh of the screen. The live hatchlings were then counted, separated from the dead shells and transferred to another incubation tank for weaning. The resulting hatching rates were subjected to Analysis of Variance (ANOVA) procedure using the package Genstat software (Genstat, 13th edition) for Windows to assess for any differences. The Duncan’s Multiple Range Test was used to discriminate among means (Duncan, 1955) at the 95% significance level (p<0.05). The cost of using each of the hatching substrates was also assessed by accounting for all expenses incurred for each of the methods evaluated.

Results

Table 1 shows the mean number of hatchlings on different substrates. It was established that Nile Cabbage ranked best, trays were second while Kaka ban mats were last. This difference between the means of the hatchings was then expressed in hatching rates and this further supported the ranking of these three substrates (Figure1).

Figure 3. The percentage hatching rates of different treatment and substrates

The costs incurred in the use of the substrates were indirect costs. These costs emanated from opportunity costs such as labor costs involved in extracting, making and collecting the substrates. The kaka bans mats were obtained from nylon sacks carrying the fish feeds; trays were made from old hapa nets used in farm while Nile cabbage was collected from a pond reserved for them. However, following the market prices at the time of the study, the cost of using the three substrates showed no significant difference (Table 2).

Discussion

The significance of carrying out the above experiment in aquaria tanks is to minimize labor costs and save on time involved in collecting hatchlings from concrete tanks or ponds, also in avoiding mortality due to stress (Macharia et al 2005). The results indicate that the nile cabbages performed better than the other two artificial substrates. Thisbetter performance could probably be attributed to the general principle that during incubation, the individual eggs should be well oxygenated for maximum hatching to occur (De Graaf and Janssen 1996; Hogendoorn, 1980; Viveen et al 1985). To ensure homogeneity and proper aeration of the eggs, running water was used in addition to pumping oxygen through the oxygen balls from a head box.Contrary to (Obuya et al 1995), 25% hatching rates in Western Kenya, Pistia roots exhibited high hatching rates of 47% and 59.8%. The experiment above further confirms the findings of (Macharia et al 2005) that the eggs can be allowed to stick to the roots of floating substrates such as Nile cabbage or water lettuce ( Pistia stratiotes). The lower percentages by Obuya could be attributed to not only the substrate used but also inadequate nutrition during the nursing phase and careless nursery management practices.

These higher hatching rates of Pistia roots compared to the Kaka ban mats and trays can probably be attributed to a several factors. This includes its floating ability, and thin fibrous roots that seemed to allow higher aeration of the eggs during incubation and easy separation of the hatchlings from the dead eggs, as long as the distance between the roots of the plant and the hapa bottom is kept at 15-20 cm (Macharia et al 2005). After hatching the larvae sink to the bottom of the tank while the egg shells remain stuck to the roots of the water lettuce (De Graaf and Janssen 1996).Despite these favorable incubation traits of Nile cabbage, the plant exhibits weedy overgrowth behavior especially in water with high nutrient content. For this reason, the plant should not be kept in the same pond as fish since they will probably block the gas exchange at the air-water interface.Trays performed better than Kaka mats with having trays means of 22.9% and 12.9% respectively. This can probably be attributed to the screen (mesh size 1 mm) on the trays which allow the hatchlings to, pass through the screen while the dead eggs and shell remain on the screen. This avoids hatchling infections and consequent larval mortalities. Kaka ban mats performed poorly probably due to low dissolved oxygen levels at the bottom of the aquaria tank (Macharia et al 2005).

In this research, the hatching rates of eggs on three substrates, especially that of the Nile Cabbage, were high as compared to the hatching rates recorded in some fry production centers in Kenya where other substrates are commonly used (Macharia et al 2005; Obuya et al 1995). This study, therefore, recommends the adoption of Nile Cabbage as a hatching substrate for small-scale fish farmers as it’s cheap and can be easy grown by these farmers. However, it should be grown separately due to its adverse effect as a “water pest” (Figure 4).

Figure 4. Overgrowth of the Nile cabbage in a fish pond

Conclusions

Nile Cabbage ranked best in performance with a mean hatching rate of 267; trays were second with a mean rate of 115, while kaka ban mats were last with an average of 65. There were minimal costs incurred in the use of all three substrates.

Acknowledgement

The authors gratefully acknowledge the Kenya Marine and Fisheries Research Institute - Sagana Aquaculture Centre for sponsoring and providing the research facilities

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Received 9 March 2017; Accepted 9 July 2017; Published 1 September 2017

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