COLLECTION OF SAMPLE
For the present study purpose gift tilapia, Oreochromis niloticus was collected from the Golden farm, Neyyatinkara, Thiruvananthapuram district of Kerala. The collected fishes were maintained and cultured by using selected feeds.
MAINTENANCE AND CULTURE OF FISHES
In the present study 1cm mean sized fishes were introduced into different cement tanks of well oxygenated good quality water. In each experimental container 20 fishes were introduced. Four different diets were given to the fishes in four different tanks. All the experimental trials were done in triplicates and their average was taken for data analysis. Every day, they were fed two times. For the period of three months they were maintained to analyse different assessments of their growth performance.
Rice, ground nut oil cake, turmeric, corn, Green gram.
Rice, dry shelled fish, wheat, fenugreek and corn.
Growfin (readymade feed obtained from farm)
Different ingredients selected to formulate the feed were separately sun dried and crushed well using a mixer grinder to small particle size. A sieve was used to remove large particles or foreign materials which can damage the machinery. The ingredients were weighed and appropriate quantities were taken for feed preparation.
1. Control Diet [CD]
The control diet was prepared by adding different amount of ingredients such as 25gm rice flour, 25gm ground nut oil cake; 5gm turmeric powder, 20gm corn flour and 25gm green gram were taken. The modified method of Gull et al. (2005) was adapted. With the help of warm water the dry ingredients were mixed slowly. Good mixing can improve palatability. Water was added and mixed well to form a mash with a cake like consistency. As a general rule, the total moisture content of the mash should be in the range of 45 to 55% to produce good pellets. Pass the feed mash mixture through a pellet machine (mincer) with 1mm diameter. The mash was then steamed in a food steamer for about 10 to 15 minutes. Later it is cooled and kept in the refrigerator for 48 hours. This mash was then dried in the room temperature and cut the extrusion (which looks like noodles) into similar length to the closest pellet diameter. The moist pellets were then dried to moisture content of 10% or less simply by spreading the pellets under the sun rays.
2. Diet 1[D1]
This diet was prepared by taking 25gm rice flour, 25gm powdered shelled fish, 25gm wheat flour, 10gm fenugreek and 15gm corn flour and mixed thoroughly to make an emulsion with the help of warm water. Mix with dry ingredients slowly. To improve palatability the contents were mixed well. By the addition of needed water the mash with a cake like consistency was formed. The total moisture content of the mash should be kept in the range of 45 to 55% to produce good pellets. Pass the feed mash mixture through a pellet machine (mincer) having 1mm diameter. The mash is then steamed in a food steamer for about 10 to 15 minutes. Later it is cooled and kept in the refrigerator for 48 hours. This mash is then dried at the room temperature and cut the extrusion (which looks like noodles) into similar length to the closest pellet diameter. The moist pellets were then dried to reduce the moisture content of 10% or less simply by spreading the pellets under the sun rays.
3. Diet 2[ D2]
Grow out (commercial) feed was bought as a readymade feed from the aquarium to fed the fishes in the third tank.
4. Diet 3[D3]
Azolla (natural feed) were given to the fishes in the fourth tank directly without any modification of the feed.
FEEDING THE EXPERIMENTAL FISHES
Correct delivery of food is important to reduce feed waste. Underfeeding can result in loss of production while overfeeding results in feed wastage and can lead to deterioration in water quality. A serious decline in water quality can result in loss of stock and the need for corrective measures. The fishes were fed twice a day preferably after sunrise (7 to 9 am) and before sunset (4 to 6 pm). 2gm of feed was provided to fishes in each container every time.
ESTIMATION OF LENGTH - WEIGHT RELATIONSHIP
The length and weight of the fishes (Jisr et al. 2018) from each container were measured at every 15 days to estimate the length – weight relationship. Fish was measured in terms of weight gain and increase in length. Total length (TL) was measured to the nearest 0.1mm using 30cm ruler as the distance from the tip of the anterior most part of the body to the caudal fin while weight measurements were taken in gm using 0.01g sensitive weighing balance at an interval of 15days.
1. Relative growth (RG)
It is used for the comparison of the size of similar organisms. RG is calculated with the formula quoted here.
2. Relative growth rate (RGR)
RGR is the growth rate relative to the size of the population. It is calculated by the following formula.
3. Specific growth rate (SGR)
The specific growth rate is defined as the rate of increase of biomass of a cell population per unit of biomass concentration. Weight was recorded in grams. It is calculated by using the following formula (Steel et al. 1997).
SGR = Log[Final weight] – Log[Initial weight] ×100
4. Feed conversion ratio (FCR)
The success of an aquaculture practice is dependent upon many factors relating to the field of biology, engineering and economics. The feed conversion ratio is a remarkable tool for understanding the acceptability of given feed (Inayat and Salim, 2005). FCR is calculated using the following equation.
Where F is the weight of food supplied to fish during the study period; Wf is the live weight of the fish at the end of the study period; W0 is the live weight of the fish at the beginning of the study period
5. Length- weight relationship
The Length - weight (log transformed) relationships were determined by linear regression analysis and scatter diagrams of length- weight were plotted. The length – weight relationship of the experimented fish was worked out as per cube law given by Le Cren (1951).
Where, W= Weight of fish (g), L is observed total length (cm), ‘a’ is the regression intercept and ‘b’ is the regression slope.
The logarithmic transformation of the above formula is
Log W= log a +b log L
6. Fulton’s condition factor (K)
Fulton’s condition factor (K) was calculated according to Htun- Han (1978) equation as per formula given below:
K = x 100
Where W= weight of fish (g), L= length of fish (cm).