E.M. Amin
The total body energy stores of European silver eel (Anguilla anguilla L.) at the start of migration is sufficient to fulfill all biological activities which begin with active migrations. We used a slightly modified model to evaluate the energy budget of eel during gonadal development, migration and spawning.
Lipid and protein are the main energy components of eel body; lipid is the principal source and protein represents the second source of energy. Lipid energy, as a percentage of total energy, was 58.2 for male and 67.9 for female yellow eels. These values were smaller than those calculated for male (76.3) and female silver eels (80.1).
Lipid energy of immature testes amounted to 72.5%, while immature ovaries contained 83.9%. Further gonadal development showed an increase in lipid energy up 80.3% at time of formation of spermatozoa in the ripe male and 86.4% at the time of ripe ova in the female ovary.
About 25.1% and 20.3% of the total energy expenditure seemed to be utilized in oogenesis and spermatogenesis, respectively. Approximately 17.1 and 15.8% of total energy was utilized for ovulation and spermiation, respectively. During migration and simultaneous routine metabolism (ER) about 35.7 and 34.2% of the total energy was utilized by female and male silver eels, respectively.The energy of routine metabolism was higher in male than in female silver eel, with values of 9.6% and 6.0%, respectively.
A.Q. Siddiqui, M.S. Howlader and A.A. Adam
Three experiments during a growing season of 210 days (April- October) in Al Hassa region of Saudi Arabia demonstrated that Nile tilapia (Oreochromis niloticus L.) could be grown from an average weight of 20 g to over 300 g in concrete tanks giving a production of about 20 kg/m3 with a stocking density of 64 fish/m3. Drainage water was flowing through the tanks at the rate of 1 L/min/kg fish biomass, the tanks were uniformly aerated and a commercial fish feed with 34% dietary protein was fed to the fish. To provide 20 g fingerlings for early stocking, the fingerlings should be produced in September- October and overwintered for early stocking in April. The fingerlings produced and stocked in the same growing season will not reach minimum marketable weight of 250 g.
The fingerlings (av.wt. 4 g) stocked at a density of 40/m3 in triplicate tanks attained an average weight of 544 g with a corresponding yield of 21.7 kg/m3 in 415 days. Average food conversion ratio was 2.16. In another experiment 64 fish/m3 with an average weight of 19 g were stocked in duplicate tanks and reared for one full growing season. An average weight of 361 g and average yield of 23.1 kg/m3 were obtained. The average food conversion ratio was 2.14. In the third study the fish had an average weight of 40 g and were stocked at a density of 42.6/m3 in duplicate tanks. They attained an average weight of 323 g in 164 days which gave an average yield of 13.4 kg/m3. The food conversion ratio was 1.96