FIELD STUDY ON THE EFFECT OF DIFFERENT TIMES OF EXPOSURE DURING HORMONAL PRODUCTION OF MONOSEX TILAPIA ON THE GROWTH RATE AND HEALTH CONDITION DURING THE CULTURE SEASON

 

M.A. ABD EL-AZIZ

 

Department of Fish Diseases and Management Fac. of Vet. Med. Cairo University

 

ABSTRACT

In this field study, 3 groups of sex reversed tilapia through hormone treated feeds were done by 60 mg\kg food of methyltestosterone for 3 different times (14-21-28) days. At the end of the exposure time, the mean survival rate and average weight were determined for each group. Then 30.000 fry from each group were cultured separately in strictly the same conditions till the end of the culture season.  Samples of fish from each group were obtained every 14 days along the culture season to determine the average weight, total length and food conversion. At the end of the culture season the total mass production for each group was determined. Also the general health condition and fish reflexes were observed for each group along the culture season. The results revealed that the exposure of fish for hormone treated feeds for 28 days was associated with higher growth rate, higher food conversion and total mass production than the other 2 groups, with no significant changes in the mean survival rate and total length after the end of the exposure time and along the culture season. From these results it  could be concluded that (28) days is an appropriate time for the hormonal production of monosex tilapia .  

 

INTRODUCTION

In the recent years culturing of fish was encouraged and developed all over the world in order to cover the shortage in animal protein, specially when put in our consideration that the obtaining of fish from natural resources becomes more expensive and harder as a result of increase the cost of fishing as well as depletion of many stocks in natural water due to pollution (Ninawe, 1998).

Some fish species have been chosen and succeeded in culture application depending on some characters as growth rate, resistant to diseases, dressout percentage, reproduction under captivity, food availability as well as consumer acceptance (Laird and Needham 1988).

Tilapia species (Oreochromis species) have all these characters in addition this species is highly tolerant to poor quality water (Landau., 1992). So it considered one of the most important cultured species in Egypt and now this group of fish is highly popular in aquaculture in Africa, Asia and other parts of the world.

At the same time a very important problem involving culture of tilapia is what is called over population (super population) which resulted from that many species of tilpia spawn at very young age and some reported to have spawned at a length only slightly exceeding 10 cm (Chimits, 1955; Mair and Little 1991; Little et al 1995; Afanso et al 2001) resulting in a very large number of small tilapia of no economic value at the time of marketing.

A variety of methods have been utilized to overcome this problem (Kumar, and Tembhye, 1996; Bhujel, et al 1998), firstly attempts have been made to control over population by stocking carnivores as catfish which consume small tilapia fish but this method have several disadvantages. Other method of maintaining stable tilapia population includes the use of cage culture but it also associated with many drawbacks.

The ideal solution found is the culturing of monosex tilapia. The steps directed to produce male tilapia because it generally grows more rapidly than the female (Green, and Teichert 1994)) specially when the fish approach adulthood and the female begin to divert large amounts of food energy to egg production. Thus the production of all male population of tilapia not only solves the over population problem but also leads to more rapidly growing animals.

            Monosex production can be achieved by 3 methods, firstly by hand selection but very difficult in young age of tilapia (Baroiller, and D’Cotta, 2001), secondly through hybridization between different species of tilapia but extra-facilities are needed to maintain 2 or more species of brood animals compared to those required for maintaining only one species. So the monosex production through hormones considered the most applicable method (Carrasco et al 1999).

At the same time the culturing of hormonal sex reversed tilapia is associated with various results specially regarding the growth rate of these sex-reversed fish. The marked variation in growth rate among sex reversed tilapia is commonly related by the fish farmers and aquaculturists to the source of obtaining these frys (varied from fish hatchery to another) and not to any other factors.

So the aim of  this field study is :

-Determination of the effect of different exposure time  to hormone treated feeds which is famous as a main factor on the growth rate and health condition of sex reversed tilapia during the culture season.

Which is achieved through :

-Determination of the mean survival rate and mean weight for each group at 28 days age and after exposure to hormone treated feeds for 3 different times.

-Determination of the growth parameters (mean weight, total length and food conversion rate) for each group after one month of culturing in the earthen ponds and till the end of the culture season.

-Determination of the total mass production for each group at the end of the culture season.

-Evaluation of the health condition of fish from each group through macroscopical examination as well as observations of fish reflexes along the culture season.

 

MATERIALS AND METHODS

About 150,000 tilapia nilotica fry were collected from the spawning tank and were classified into 3 equal groups each group about 50,000fry. The frys were fed a standard fish diet containing 55% protein and treated with 60 mg of methyltestosterone for each kg food according to ( Bhujel, et al 1998). The hormone treated feeds were offered for 3 different times adjusted as 14 – 21 and 28 days for the group 1,2 and 3 respectively. The same feeds but free from hormones were given to group 1and2 for 14 and 7 days respectively to complete the period of 28 days.  After the end of this period, the mean survival rate and average weight were determined for each group.

After that about 30,000 frys from each group were transferred and hold after adaptation in 3 earthen ponds each one sized about 3-acre. All conditions were adjusted in the 3 ponds to eliminate any exogenous factors that may affect the growth of any group than the others. The 3 ponds were supplied from the same water source and the rate of change of water was stable in them, also the fish in the 3 ponds were fed on formulated pillets containing 25% protein, 2.6%crude fat and 6% crude fibers which meet the nutritional requirements of tilapia fish (Diana et al 1996). The 3 ponds were fed at feeding rate 10% finely grounded ration 4 times\day for one month from (4-6-2001 till 4–7-2001) then at feeding rate 3% 3 times\day till the end of the experiment. The water parameters along the experiment was measured according to (APHA, 1989) and no difference was found among the 3 ponds, the dissolved oxygen ranged from (5.6-6.9) mg\L, the pH was (7.4-8.2) and the temperature During the culture season was optimum for the growth of tilapia (20-32c).

After one month from descending of fish, when the fish becomes easily handled, samples of fish were obtained from each pond every 14 days to determine the growth parameters (average weight, total length and food conversion rate) according to (Rahman et al., 2001). Also the health condition of the fishes in the 3 ponds was evaluated through macroscopical examination as well as observations of fish reflexes according to (Stoskopf 1993).

 

RESULTS

The results revealed that there was no significant variation in the mean survival rate among the 3 groups.  It was about (80-82%) of the stocking density which means that the different times of exposure to hormone treated feed has no significant effect on the mean survival rate of tilapia fry.

The results of determination of the average weight at the same age (28days) after exposure to hormone treated feed at 3 different times(14,21 and28days) which completed by feeds free from hormones in group 1 and 2 till 28 days age revealed that the mean average weight for the group (1and 2) where the frys exposed to hormone treated feed for (14and 21) days was 1100 gm\1000 fry which means that the mean average weight for each fry was 1.1 gm while in the group 3 where the frys were exposed to hormone treated feed for 28 days, the mean average weight was 1250 gm\1000 fry which means 1.25 gm for each fry.

Determination of the growth parameters as seen in table (1) revealed that the fish in group (1) where the hormone treated feed was offered for 14 days was rapidly grow similar to the fish in group (2) till the age of about 90 days then the growth pattern significantly slowed in comparison with the other 2 groups till the end of the experiment. The average weight for each fish in-group (1) at the end of the experiment (180) days was about 222.2 gm with 9-fish\2kg weight. The results also showed that the average weight of fish in group (3) where the hormone treated feed was offered for (28) days was significantly higher than the other 2 groups from the beginning till the end of the experiment. The fish in-group (3) reach 250 gm average weight 2 weeks before the fish in group (2) and longer period in comparison with fish in group (1).The results of determination of the total length revealed that there was no significant variation between the fish in the 3 groups.

At the end of the experiment the total mass production for each pond was calculated in comparison with the total amount of artificial feed given which was 15 ton for each one. The results indicated that the total  mass production was 5625 kg for the first group, 6150 kg in the second group while in the third group was 6870 kg which means that the food conversion rates  were 0.375, 0.410 and 0.458 for group 1,2 and group 3 respectively. The examination of the fish in the 3 groups along the experiment revealed that the general health condition of fish were somewhat similar, the fish in the 3 groups exhibit normal ocular, tail and defense reflexes as well as feeding and escape reflex. Little erosions of the caudal fin were common in fishes in the 3 groups, which may results from the nature of water in this area.    

 

 

 

 

Table 1

 

DISCUSSION

As discussed before that different methods have been used for the controlling of the problem of over population, it could be analyzed that only the hormonal treatment of fry has the ability for the production of single sex fish stock, specially when the treatment is made with the correct dosage, at the correct time and for the correct length of time (Bhugel, et al 1998; Gale et al 1999), as tilapia is one of the species in which sex can be reversed easily by administration of sex hormones at early stages of development (Donaldson, and Hunter, 1982; Lam, 1982; Oliveira, et al 2001).

The results of this field study revealed that the growth rate of fishes in group (3) where the fish exposed to hormone treated feeds for 28 days was higher than the other 2 groups where the fish exposed to hormone treated feeds for 21 and 14 days respectively. This variation in growth rate was noticed earlier after the finishing of hormonal treatment period and was emphasized along the experiment where the fish in group (3) reach to the market size (250) gm very earlier than the group (1) where the hormone treated feeds offered for 14 days and also earlier than the group (2) where the hormone treated feeds was given for 21 days.

The fish in group (3) reach the market size (250.6)mean weight at date 21-11 while the fish in group (2) reach the same size at date 5-12 (14 days later than group 3) which has a great economic value, as fish in each group eat about 200 kg/day, total 600 kg/day in the 3 ponds and total 8400kg/14 days, in addition to the money lost in wages and fuel during this period.

The marked slow growth rate of fish in group (1) where the growth rate significantly slowed down at about (90) days age and continue till the end of the experiment, which may results from that the exposure time to hormone treated feeds wasn’t enough to induce high percentage of sex reversed fish and so a percentage of females in the pond begin to divert large amounts of food energy to egg production (stickney, 1979), which results in large numbers of small fish that was clear among the fish in group (1) at the time of harvesting. These small fish share with the large fish in food and so the final average weight, food conversion and total mass production was lower than group (2) and group (3).

The highly significant results that were associated with group (3) where fish exposed to 17 alpha methyl testosterone treated feeds for longer time than the other 2 groups may triggered by the effects of this exogenous androgen, as this anabolic hormone when given by mouth, rapidly absorbed, metabolized and converted by the enzyme 5 alpha reductase into dihydrotestosterone which bind to androgen receptors resulting in an increasing of protein synthesis, enhancement of muscle development, leading to higher growth rate and so have the general growth promoting properties. So this hormone commonly used in humans as protein anabolic agent, also for treatment of refractory anemia as well as metabolic stimulator (Katzung, 1989;Rang and Dale, 1994).

The rapid growth rate associated with culturing of monosex tilapia reduce the culture time to be about 180 days which enhance greatly the production of tilapia in Egypt and reflected on the price of tilapia fish now.. Also it could be concluded that (28) days as a time of exposure to hormone treated feed  is an appropriate time for the hormonal production of monosex tilapia, because most fish hatcheries in Egypt specially in Kafr El Sheikh governorate, where hatcheries cannot cover the requirements for seeds apply only 18 and 21 days exposure time to hormone treated feeds, which has an economic draw back as documented in this field study.  

Also the results revealed that the exposure time to hormone treated feeds had no effect on total length as well as on the general health condition of exposed fish. The general health condition in the 3 groups was normal and the common meaning by the fish farmers that sex reversed tilapia is highly sensitive and weak than the normal tilapia wasn’t marked completely.

 

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