Date of Award

2005

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Environmental Science

First Advisor

Dr.Waleed Hamza

Second Advisor

Dr. Ibrahim El-Shishtawy

Third Advisor

Dr. Hazem A. H. Kataya

Abstract

The importance of fish aquaculture in general as an alternative source of animal protein, is raised during this century after the significant reduction of natural marine resources. Such reduction has increased the interest of many countries as well as international agencies in worldwide food security, especially for developing countries. The success of any aquaculture is chiefly judged by its economic development, which always depends on the management of producing acceptable marketing size and weight of fish in short time. In the last few decades, many aquacultures failed in balancing between the financial input and the resultant income. That is due to many reasons; one of them is the high mortality in fish fry which resulted from either the difficulty of obtaining a suitable diet (live food) or from the quality of the living conditions of the cultured fry.

In the Middle East countries especially, and in Asia as general, certain fish species are becoming the most cultured ones because of their high consumption and because of their acceptable commercial price by local populations. However, in the last few years, such prices have increased, due to many reasons. These include, the increase of artificial diets items and the high mortalities of fish fry due to the lack of the food necessary to the fry immediately after its hatching. A viable example is Tilapia nilotica species (Oreochromis niloticus).

In the present study two types of experiments were designed to investigate the effect of different food sources on the growth rates of Nile tilapia fry (Oreochromis niloticus), and to evaluate the effect of some culture conditions on the feeding behaviour of the fry. In the first experiment, the effects of three types of food (ChIorella vulgaris, Artemia fransciscana, and Artificial feed) and various combinations of the three types (ChIorella + Artemia; Chlorella + Artificial feed; Artemia + Artificial feed; and Chlorella + Artemia + Artificial feed) on the growth, feed utilization and survival of Nile tilapia fry has been investigated, with average initial weight of 12 mg fry-1. Tilapia fry were cultured in a closed system and fed with seven feed combinations. Triplicate groups of fry with 24 fry per 6 L tank were used for each treatment. The diet was offered 3 times a day, for 35 days. The results indicated that the maximum body weight and survival was achieved by fry fed on Artemia, followed by those fed on the combination of the three food types, then by Artemia + Artificial. On the other hand, the minimum growth and survival were observed from the fry fed only with Chlorella suspension. The fry fed only with Artificial feed showed moderate growth and good survival.

In the second experiments a series of trials were carried out to detect the response of tilapia fry to live food suspension of Chlorella, Artemia, and Artificial feed, and the smell of the filtrates of the Chlorella, Artemia and Rotifers cultures. Another trial was designed to study the response of tilapia fry to different environmental opaque colours (green, yellow, red, and blue). These experiments were carried out in a rectangular glass basin divided into six tracks using five longitudinal transepts. These tracks were used as swimming pools. At both ends of each track mobile doors were inserted to separate a small chamber.

In the food suspension experiment, the basin was filled with tilapia fish tanks water. The mobile doors were tightly fixed at both ends. The small chambers of two tracks were filled with Chlorella on one side and with experiment water on the opposite side. The chambers of another two tracks were filed with Chlorella on one side and Artemia on the opposite side, while the remaining two track ends were filled with ChIorella on one side and Artificial feed on the opposite side on the suspension experiment.

For the smell experiment the basin was filled with tap water and the Artificial feed replaced by Rotifers. Also, the doors of the chambers were raised about 0.5 cm in the beginning of the experiment. Five tilapia fry were introduced into the middle of each track at the beginning of the experiments. The movement of the fry towards one source of food/extract or another was recorded every 5 minutes for a total of 30 minutes. The same process was followed on the four colour experiments but with a little modification: the doors of the chambers were removed and sheets of opaque colours inserted in the end of champers. In each experiment, a single colour was examined against the other three, as well as against itself.

The results have shown that the tilapia fry favoured the suspensions of Artemia nauplii and Artificial feed more than the Cholorella suspensions. Furthemore the tilapia fry were attracted by the smell of Artemia and Rotifers filtrates more than the filtrate of the Chlorella culture. However, the chlorella filtrate was highly attractive to the fry compared with the blank conditions. Results from the color experiments showed that green is the most attractive color followed by yellow then blue, while red was the least attractive one.

In conclusion, Artemia nauplii was the best live food, followed by Artemia nauplii combined with Artificial feed, to accelerate the growth rate of the fry. Moreover, it is recommended to use algae extract which may act as a natural colouring agent as well as an odour stimulator.

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