| Livestock Research for Rural Development 28 (10) 2016 | Guide for preparation of papers | LRRD Newsletter | Citation of this paper |
This study was conducted over a period of nine weeks to investigate the population of zooplankton raised in concrete tanks, using organic manures, as an alternative to imported expensive Artemia cysts (INVE®, USA). Cow dung, swine faeces and their mixture (50:50), were used in quantities of 1.50 g/litre, 0.46 g/litre and 0.98 g/litre, respectively, to fertilize the culture tanks under an outdoor management system. Zooplankton population was monitored for 53 days with a compound microscope and an improvised 250µ mesh-sized zooplankton net. Representative species of Cladocera and Copepoda were preserved in 70% ethyl alcohol and taxonomically identified.
Results revealed that there were no significant differences (p = 0.05) among the mean zooplankton populations of the three treatments. While a significant relationship (p = 0.0098) was found between zooplankton population in cow and mixture manure-fertilized tanks, and number of days, the case was different in the swine manure fertilized culture tanks (p = 0.01). Furthermore, the temperature (25±20C) of the culture tanks during the study period had no significant effect (p = 0.01) on the zooplankton population across the three treatments. Therefore, cow and swine manures can be used to raise zooplankton under extensive outdoor conditions, as an alternative to imported expensive Artemia cysts (INVE®, USA) for feeding larvae and fry of African catfish.
Keywords: cladocera, copepoda, organic manure
Fish farming is one of the means of efficiently increasing food production in developing countries. It is a channel for reducing poverty and improving rural livelihood under appropriate circumstances (Jamu and Ayinla 2003). African catfish has been the most preferred fish species cultured in the tropical and sub-tropical countries owing to its adaptive features and market acceptability. Many African countries have benefitted from the culture of catfish and other fish species in meeting the dietary protein requirements of their citizens as well as generating income and foreign exchange, depending on the scales of production employed.
The importance of cultured fisheries in Nigeria cannot be undermined owing to declining harvest from capture fisheries. The shortfall in landings from natural water bodies has been attributed to over-fishing, habitat destruction and pollution, among other factors. Reduction in fish landings from the wild has primed aquaculture as the best alternative to bridging the widening gap between fish demand and supply, as well as ensuring fish for all, irrespective of their economic class. According to Ozigbo et al (2014), available statistics indicate that the nation’s growth in fish production is due to increased production from aquaculture. Besides ensuring growth in fish production, aquaculture provides a more predictable fish supply source than capture fisheries, which is more susceptible to environmental and climatic constraints (Adetunji et al 2009).
Meeting dietary protein requirements from fish consumption is crucial in developing countries, where malnutrition remains a major problem faced by millions of poor citizens. The awareness on the unlimited capacity of aquaculture to provide employment, enhance nutritional security and provide several livelihood opportunities, especially among the low-income populace, has improved drastically in Nigeria. This will not only increase the earnings of the farmers, but also reduce huge loss of the nation’s resources to continuous importation of frozen fish among other fish products. As reported by Mgbakor et al (2014), recent findings showed that aquaculture production in Nigeria stands at about 200,535 metric tonnes per annum, representing 24.5% of the total domestic fish production. Consequently, Nigeria needs about 1.8 to 2.6 million metric tonnes of fish annually to satisfy her fish demand and meet 13.2 kg per capital global requirement for fish consumption.
Recent development in the Nigerian aquaculture sector has given birth to an exponential number of fish farms, where Clarias gariepinus, African catfish, is being raised in monoculture and polyculture systems. This is partly due to the hardiness of the species under captivity, strong consumer preference and the high market value it commands. In addition to the above properties, the ability of C. gariepinus to feed on a wide array of natural prey under diverse conditions, coupled with fast growth rate, has been exploited under extensive and intensive management systems. Relatively low input and high return on investment favour catfish and tilapia culture among fish farmers (Omitogun and Aluko 2002). Olaleye (2005) reports that use of African catfish in pond culture have been encouraged in the African continent. In Nigeria, however, the outputs of both government- and private-owned hatcheries have not been enough to meet the farmers’ demand for catfish fry and fingerlings. Proper larval and fry nutrition is important for high fry and fingerling survival and rapid growth. Even though aquaculture has gained the attention of many entrepreneurs, who are investing huge capital, relatively low production cost is an important factor that cannot be ignored, in the Nigerian context, to allow participation of low income earners in operating catfish hatcheries as well as raising catfish in general.
The use of feed produced from locally available feedstuffs, which do not
compromise the nutritional requirements of the fish species under culture,
allows reduction in cost of production. Likewise, the replacement of
Artemia, the conventional imported feed for the larvae and fry of
African catfish, for a less expensive natural feed is necessary to reduce
the production cost and improve the profit margin of farmers. An example of
such less expensive natural feed is zooplankton raised using local
technology. Culturing zooplankton for hatchery use at relatively low cost
will enhance fingerling production at sustainable levels. A 500 g can of
imported Artemia cysts (INVE®, USA) costs about N
6,500 (six thousand five hundred naira, equivalent to 33 US dollars) in
January, 2016. In view of this, effort aimed at mass production of planktons
using locally developed methods need to be reawakened. A typical example of
such local method is the use of organic manure to raise various species of
zooplankton (NIFFR 1996).
Organic manures, especially from animal sources, are not only cheap and readily available, but also ensure consistent production of the algal bloom and consequent zooplankton growth. Various studies (Ovie et al 1993; Adeyemo et al 1994; Ovie et al 2000) have tried the use of single zooplankton species as potential live food for weaning catfish fry. However, Jeje (1992) argues that mass culture of mixed zooplankton species for hatchery operations is more realistic in Nigeria. He submits that the techniques involved are easier to master by farmers than monoculture of species. In spite of this, the production of zooplankton using different organic manures has not been extensively documented. Therefore, this study examined the population dynamics of zooplankton raised on cow dung, swine waste and their combination under an outdoor management system.
The study was carried out over a period of nine (9) weeks (August-October, 2015). The experiment was conducted in six (6) outdoor concrete tanks with a dimension of 0.65 m by 0.53 m by 1.28 m. Concrete tanks were used in order to simulate the natural conditions of an outdoor system.
Tank preparation involved washing with water, disinfection and exposure to continuous sunlight for 48 hours. This became necessary to remove filamentous algae and predators of zooplankton such as dragonfly larvae, diving beetles and backswimmers. Humus was evenly spread on the floor of the sun-dried tanks to a thickness of about 1cm in order to minimize error due to differences in the condition of the tanks. The tanks were impounded gently to 0.64 m depth with 220 litres of water, and left to stand for a period of 4 days to allow for de-chlorination. Selected water quality parameters (pH, temperature, dissolved oxygen, total alkalinity and hardness) of the water source were measured at the early hours (between 7.00 and 8.00 hours) of the day prior to tank impoundment. Mosquito net of 1.8mm mesh size was used to cover the set-up to prevent the entry of predatory aquatic insects, insect larvae and amphibians.Fresh organic manures, mainly cow dung and swine faeces, collected from the Beef and Swine Units of the Obafemi Awolowo University Teaching and Research farm, Ile-Ife, were used to fertilize the tanks in order to provide adequate nutrient base for plankton emergence and growth. The choice of the manure source was to ensure that additive-free organic manures were used for the experiment. The feed additives, sometimes administered to livestock to control flies and their larvae, may inhibit the production of zooplankton, especially cladocerans. The manures were transported in dry, clean black polythene bags to the wet laboratory of the Department of Animal Sciences, Obafemi Awolowo University, where they were weighed and soaked in specific rates. In line with submission of Rottmann et al (2003), the cow dung and swine faecal manures were used at starting dose rates of 330 g and 100 g respectively. Half of the 2 manure rates on a 1:1 ratio were mixed to constitute a manure mixture. Each of the three manures rates, were replicated twice and soaked in covered plastic containers buckets with 10 litres of water. The soaked manures were stirred twice daily and allowed to ferment for 3 days. The resulting manure solution was filtered using 1.8 mm mesh size sieve; the residue was discarded while the filtrate was used to fertilize the prepared zooplankton culture tanks. Limited number of available concrete tanks restricted the number of replicates for each treatment to two.
Poor algal concentration of the fertilized cultured tank observed prompted the application of second fertilizer dose. The low algal emergence was observed using a clear glass, as against a slightly cloudy green or tea colour, which signifies sufficient algae content necessary for zooplankton development. The insufficient algal content, as shown by the clarity of the culture water, was further confirmed using the ‘Human arm method’ (NIFFR 1996) of measuring water turbidity. The arm was visible under the water beyond the 2-times-the-elbow length. Consequently, additional fertilizer dose, same as the initial rates, was added in form of fermented filtrate which led to zooplankton emergence.
Concentrated sampling from five different points was carried out in each of the tanks at two days interval. Sampling done out between 7.00 and 8.00 hours on sampling days using a 250 µ-mesh-size improvised plankton net (Plate 1). Prior to each sampling, the temperature of the pond water was measured with a mercury thermometer. Counting of zooplankton in 10 sub-samples taken from each collection bottle was carried out in a petri dish using a hand magnifying lens while zooplankton population in each of the randomly taken sub-samples (4 ml) was recorded. At high population densities, the movement of the zooplankter was arrested with 1ml of 70% alcohol to ease accurate counting. Slides of zooplankton, notably copepod and moina, were prepared by isolating each of them on an evaporating dish, dehydrated using graduated ethanol (30, 50, 70 and 100%), mounted on a clean microscope slide and covered with cover slip. Slides were examined using a Leitz microscope and viewed at 4X and 10X magnifications. Descriptive and inferential statistical analyses were used to evaluate the relationship between the length of culture days and zooplankton populations, relationship between kind of manure used and the population growth, and effect of ambient culture water temperature on zooplankton population.
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| Plate 1. Improvised Plankton net (250 µ) made from iron ring and “pap” sieve |
The physico-chemical parameters of potable water impounded in the culture tanks, prior to application of first manure filterate, were as follows: pH (7.70); temperature (24oC); dissolved oxygen (4.76 mg/l); alkalinity (201 mg/l); and total hardness (283 mg/l). A gradual colour change was observed in culture medium as from the fourth day after second manure filtrate application. While both swine and mixture fertilized tanks changed from yellow to light green, the swine fertilized tank changed from brown to tea colour. Zooplankton emergence was observed in the study on the 5th day after second fertilization. The trend of the mean zooplankton population density (per ml) in each of the culture tanks as the days went is shown in Figure 1.
 |
| Figure 1. Means of zooplankton population in each of the fertilized culture tanks over a period of 53 days. |
As evident on Figure 1, zooplankton population in the three treatments started rising at about the 5th day after second fertilization. The rate of rise and fall in population differs for each kind of manure used, as it assumed different values as the day of culture increased. In the cow manure-fertilized tanks, a gradual rise in population was observed till day 19 before subsequent fall and rise in the population. The peak of the population was observed at day 51, with a density of 17.5 zooplankters per ml. In the swine manure-fertilized tanks, population peaks were recorded at days 25, 27 and 31; the highest at day 27, with a density of 27 zooplankters per ml. In the mixture manure-fertilized tanks, the population peaked at day 41 with a density of 38 zooplankters per ml. of culture water. Throughout the study period, the zooplankton that emerged whose population was measured were Copepod and Moina spp. Representative samples of the two zooplankton species isolated in the culture are shown in Plate 2.
 |
 |
| Plate 2. Photomicrograph of representative samples of zooplankton species; Moina spp (left) and Copepod (right) | |
The overall mean population, standard error of the mean population, correlation values of the population in relation to the number of days and temperature of the culture ponds at the time the sampling was carried out as well as the regression equation are presented in Table 1.
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Table 1.
Effect of different organic manures on zooplankton population and the correlation with the number |
|||||
|
Manure |
Mean |
r |
r |
1
Regression equation
|
R2 |
|
Cow |
32.1 |
-0.177 |
0.844** |
Yc = 2.15 + 0.844X1 |
0.70 |
|
Swine |
34.1 |
-0.064 |
0.298 |
- |
- |
|
Mixture |
34.4 |
0.127 |
0.741** |
Ym = -12.6 + 0.741X2 |
0.53 |
|
SEM |
6.93 |
- |
- |
- |
- |
|
** Significant at the P < 0.01 (1-tailed). SEM = standard error of the mean population.
|
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The overall mean populations of zooplankton over the 53-day period in cow manure-, swine manure- and mixture manure-fertilized tanks were 32.1, 34.1 and 34.4, respectively, with a standard error of 6.93. Analysis of variance carried out on the population revealed that there were no significant differences (p = 0.05) among the mean population across the three treatments. This points to the fact that using any of the three organic fertilizers will give the same population of zooplankton over an 8-week period. This is in agreement with the findings of Rottmann et al (2003) on the use of cow dung and swine feaces as fertilizers in zooplankton culture. The standard error value for the mean population across the three treatments showed the level of accuracy in the measurement of the zooplankton population across the three treatments. The error value was presumably high, probably due to an abruptly high zooplankton population recorded in the mixture manure fertilized pond at days 41 and 43, which were 152 and 124, respectively. Owing to the coincidence of the study period with rainy season, dilution of the zooplankton culture tanks was observed due to water addition from rainfall. Due to the outdoor set-up, the increase in water volume without increasing nutrient level may have reduced the rate of plankton emergence and density. Also, sunlight that could have aided high phytoplankton emergence was inadequate, and hence led to poor zooplankton emergence. Low temperature of the culture medium, during the study period, may have also contributed to recorded zooplankton density.
Also, Table 1 reveals that there was positive correlation between the population and the number of days across the three treatments, that is 0.844, 0.298 and 0.741, for cow manure-, swine manure- and mixture manure-fertilized culture ponds. The culture water temperature was positively correlated to population in the mixture manure-fertilized ponds (r = 0.127), while it was negatively correlated to the populations in the cow manure- and swine manure-fertilized ponds (r = -0.177 and r = -0.064 respectively). However, at 1% confidence level, the result showed that there was a significant relationship (p = 0.0098) between population in both cow manure-fertilized culture pond (r = 0.844) and mixture manure-fertilized culture pond (r = 0.741), and the days. This can be attributed to the similar rates in population growth observed in the two treatments. Unlike the cow and mixture manured tanks, there was no significant relationship (p = 0.05) between the zooplankton population and the number of days despite the fact that they were positively correlated (r = 0.298). Also, there was no significant relationship (p = 0.05) between the population growth and the culture water temperature, with the range 23.0-27.00C, with average mean of 25±20C. This temperature range can be attributed to the atmospheric condition during the time in which the experiment was conducted.
Separate regression equations derived for both cow manure- and mixture-fertilized ponds reflect the specific relationship existing between the zooplankton population and the number of days. The adjusted r2 values for cow manure and mixture manure treatments, 0.70 and 0.53, respectively, meant that of the total variability in the population growth using cow manure- and mixture manure-fertilized ponds, the number of days explained about 70%, and 53%, respectively. This showed that the number of days accounted for about 70% of the population growth in cow manure-fertilized culture tanks, while the remaining 30% was accounted for by other parameters that may affect zooplankton growth. Similarly, in the mixture manure-fertilized pond, the number of days accounted for about 53% of the population growth, while the rest 47% was due to other parameters that may affect their growth.
These high percentages which the days accounted for, among other factors, is in tandem with the submission of Ovie et al (2000), that organic manures are used to provide suitable nutrients for the culture of moinids and other zooplanktonic assemblages. Similarly, Morris (1995) reveals that organic fertilizers have low carbon to nitrogen (C:N) ratios, with fine particle sizes which allow rapid decomposition. Zooplanktons consume and utilize the fungi and bacteria associated with the decaying organic materials to achieve body and population growth. However, the use of heavy doses of organic manures may cause dissolved oxygen and ammonia problems during the initial decomposition, which could result in poor zooplankton growth and survival. This confirms the need for application of appropriate quantities.
The favourable temperature condition and unlimited supply of nutrients, mainly nitrogen (N), phosphorus (P), and potassium (K), from the manures allowed increase in zooplankton population as the number of days increased till the populations reached their peaks. This is in consonance with Morris (1995) view on the use of organic fertilizers to promote desirable zooplankton species, such as rotifers, copepods, moina and daphnia. This result also follows the submission of Wurts (2004) that organic fertilizers are effective in zooplankton production in particular copepods, as well as cladocerans, especially Moina micrura and Daphnia spp in the tropical African region.
In summary, algae were the first organisms to emerge in the fertilized culture tanks; they were fed on by zooplanktons as available food resources. The copepods were observed about a week after second fertilization as whitish microscopic organism darting on a petri dish when held against a light source. Cladocerans, mainly Moina, later emerged at the third week of culture establishment. The zooplankton populations derived from the sampling process assumed varying values over the 53-day period of the study at a temperature range of 23-270C of the culture medium. Copepods, because they are swift powerful swimmers, are better able to maintain their population during the later stages of the culture season. This is in consonance with the findings of Geiger et al (1985). In general, among livestock manure, cow manure, swine manure and their mixture have been proven to be efficient in fertilizing zooplankton culture for emergence and adequate growth.
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Received 11 February 2016; Accepted 9 September 2016; Published 1 October 2016