ENGINEERING FACTORS AFFECTING THE PRODUCTIVITY AND QUALITY OF INTENSIVE FISH FARMS

Abstract

The main objective of this work is to study the effect of fish tank design parameters on water flow pattern inside the tank, and then the impact on the distribution and homogeneity of water quality parameters (Dissolved Oxygen) within fish tank, which is consequently reflected in fish productivity. The work is divided into two parts: First part was devoted to choose the number and diameter orifice entering the water to the fish tank in order to maintain the rotational velocity of water suitable for fish. While, the second experiment was carried out to study the effect of diameter: depth (geometric shape) ratio on the water movement and the impact on the distribution of the dissolved oxygen and fish productivity. We concluded from the first experiment the optimum number of holes (5,10,15,20,25 and 30 with a hole diameter of 10 and 15 mm and 3,6,9,12 and 15 with a hole diameter of 20 and 25 mm which give rotational velocities inside the optimum range to be suitable for tilapia fish at a specific flow rate (5,15,30,45,60 and 75 m3) with respect to hole diameter (10,15,20 and 25 mm). The obtained results indicated that the rotational velocity and dissolved oxygen homogeneity were obtained in the first tank of 4:1 diameter: depth ratio. The mean weight of fish increased from 18 to 148, 136 and 114 g after 14 weeks with the diameter: depth ratios 4.0, 6.4 and 8.0, respectively. The average weight gain of fish increased from 2 to 21, 8 to 13 and 3 to 6 g after 14 weeks with the diameter: depth ratios 4.0, 6.4 and 8.0, respectively. The specific growth rate ranged from 0.99 to 6.00, 0.39 to 5.25 and 0.17 to 5.10 % day-1 at 4.0, 6.4 and 8.0 diameter: depth ratios. The feed conversion rate ranged from 0.68 to 3.53, 0.88 to 10.91 and 0.93 to 18.51 kg feed/kg fish at 4.0, 6.4 and 8.0 diameter: depth ratios. The feed efficiency ranged from 0.28 to 1.46, 0.11 to 1.13 and 0.05 to 1.39 at 4.0, 6.4 and 8.0 diameter: depth ratio. The mean daily mortality rates were 0.048, 0.058 and 0.064 % at 4.0, 6.4 and 8.0 diameter: depth ratios, respectively.

Keywords: Rotational velocity, Geometric shape, Recirculating aquaculture, Dissolved oxygen, Tank geometry, Closed system.