UTILIZATION OF PLANT MATERIALS BY JUVENILE AFRICAN CATFISH (CLARIAS GARIEPINUS) AND ITS IMPORTANCE IN FISH CULTURE

SUMMARY

Juvenile African catfish Clarias gariepinus between 100 and 200 mm total length from Lake McIlwaine, Zimbabwe are able to digest plant proteins. The digestibility of three major plant proteins (maize, sunflower seed and soya meal) was 30,0, 65,4 and 84,3% respectively. C. gariepinus excreted between 27 and 55% of its soluble nitrogen as urea. Fats from one diet were found to spare proteins and to be 73% utilized.

The basal metabolic rate of juvenile catfish may be represented by the general formula:

BM = 2,56 - 0,40 (In W) - 0,10 (In W) (FS)

where BM is the basal metabolic rate in cal g₋₁ h₋₁, W is the mass in grams and FS is the feeding state (expressed as zero for a feeding fish and one for a fasting fish).

The metabolism of starving, fasting, feeding, and stressed active juvenile fish was found to be approximately 0,28, 0,56, 1,23 and 4,5 cal. g_1 h_1 respectively.

World protein shortages and the contribution that fish culture can make are discussed. Sample calculations show catfish lose up to 38% of ingested plant protein while direct consumption of vegetative material by humans results in a loss of 33% of the protein due to imbalances in amino acid make-up of plants. It is generally not physically possible to eat the quantities of traditional low protein plant material needed to obtain the necessary protein. Therefore the use of more concentrated and more digestable animal protein is necessary, and catfish with dry weight ptotein levels of 70 to 80%, are capable of acting as protein concentrators.

KEY WORDS:

• Clarias gariepinus
• digestion
• metabolism
• bioenergetics
• aquaculture
• plant protein
• feeding