The importance of aquaculture in improving the diet of the people, generating employment in rural areas and saving foreign exchange through import substitution has generally been considered in most countries of Africa in recent years. The transition from endogenous to exogenous feeding is a critical event in the life of a fish and it is generally acknowledged that live food during the first few days of hatching is necessary to ensure adequate larval survival. It has been considered that dry diets are inadequate to nourish small larvae during the first stages of feeding and that such diets could be used successfully after the larvae had been fed on live food for some time (Adeyemo, 1991). Ovie (1986) and Ojutiku (2008) named common cultured zooplankton species as Brachionus sp., Daphinia sp ,Monia sp, Cyclops sp. Copepodita sp.,Calanoid sp Adeniyi.
The use of live organisms in aquaculture has for the past decades received tremendous attention in countries where aquaculture is well developed. Faturoti (2000) noted that for Aquaculture industry to thrive apart from development of adequate manpower there is also need to research and develop various inputs of production such as feed. The cost of feeding fish fry on arterial is very high only very few farmers can afford it, also artificial feed tends to pollute water as a result there is the need to find alternative feed for fish fry.
This study was undertaken to provide baseline information that may be employed to develop a simplified hatchery technique for post larval feeding of Clarias gariepinus on zooplankton cultured from poultry manure and cow dung. The study therefore aimed at investigating the growth and survival rate of Clarias gariepinus fry fed on different natural diet sources with the view to determine the best source of production of live food for fish seed culture.
MATERIALS AND METHODS
Two major steps were involved in this experiment. They include:
||Raising of zooplankton from cow dung and poultry manure which
was raised outside the Laboratory for illumination.
||Feeding trials which were carried out inside the Laboratory.
Two plastic bowls of the same size were used for raising zooplankton. Total
300 g each of cow dung and poultry manure were collected and kept, respectively.
30 liters of spring water was added to each of the bowl and kept outside for
illumination. Each medium was constantly aerated by stirring. On the fourth
day, water sample were collected from each bowl and examined under the microscope
for identification and counting. It was repeated for 7 days. Six glass tanks
(1x0.5 m) each were used for fry rearing. Fish larvae were collected, after
yolk absorption (4th day) 60 fry were randomly selected, weighed and stocked
at 1 fry/130 mL of clean spring water in each of the tanks. Aeration of each
unit was done mechanically using aerator. Tanks A-C were fed with live food
raised from cow dung source harvested using a sieve into a bottle of about 80
mL of the medium. The same was repeated for tanks D-Fwhich were fed live food
from poultry manure as source, the experiment was repeated 3 times.
||Growth performance and survival of Clarias gariepinus fry
|S = Significant at (p< 0.05) NS = Not significant at (p>0.05)
||Final average weight (mg) and length (mm) of fry Clarias
||Average daily increase in length (mm)
Growth parameters monitored include daily increase in length (mm) of swim-up
fry right from 4 days old to the end of the experiment. Specific Growth Rate
(SRG) was obtained by using the formula below.
||Final weight of fry.
||Initial weight of fry.
||Final time (days).
||Initial time (days).
% Weight gain = W2 W1 x 100
The experimental design was Complete RandomizedDesign (CRD). The Analysis of Variance (ANOVA) was used to test for significance as well as the correlation.
The weight gained and other growth performance is presented on Table 1 and 2. Slight differences in growth and survival occurred between fry fed with zooplankton raised from cow dung and poultry dropping. The mean weight of 0.5 mg by fry fed with zooplankton raised from poultry manure was the highest, as well as the survival rate of 53.33%.
The relationship between daily increase in length (mm) of fry from day 1 after yolk absorption to day 7 (Table 3) shows that Treatment F has the highest mean daily increase 8.75 mm followed by Treatment E 8.65.
Fry fed with zooplankton from poultry manure source in treatment F had maximum
gain in length throughout the experiment 2.88 mm. Increase in length of fry
from different treatment does not follow a specific pattern. Treatment E had
the highest Specific Growth Rate of 17.45 and highest survival rate of 53.33%,
survival of 51.67% was common to Treatments C,D and F which agrees with the
findings of Ovie and Adepoju (1995), Lamai (1999) and Ojutiku (2008). The magnitude
or Specific Growth Rate, mean percentage body weight gained and mean length
gained does not correspond with the survival rate in all the experiments except
in treatment E. There was significant difference in length increase p<0.05
as also reported by Faturoti (1992). There was also a significant difference
between the length and weight p<0.05.
Conclusion: The successful feeding with small live zooplankton indicates that this could be a solution for the rearing of Clarias gariepinus fry when zooplankton can easily be obtained or cultured in circumstances where Artemia cysts are not readily available as in the case in Nigeria where the price is limiting due to high foreign exchange rate.
From all the data collected, poultry dropping is much preferable as source of raising zooplankton. It thus appeared that Clarias gariepinus is one of those species for which fry rearing requires a phase of feeding with natural, preferably live food.