Last week we released five grass carp (Ctenopharyngodon idella) into one of our dams to control the aquatic weed populations. The stocking of this species is strictly controlled by a permit system and only after a biomass assessment and investigation of our water resource, we obtained a permit to stock 5 sterile (triploid), species pure, disease free, tagged fish from De Rust Grass Carp Farm, Bonnievale, who is one of our leading accredited producers.
The grass carp is a herbivorous, freshwater fish species of the family Cyprinidae, and the only species of the genus Ctenopharyngodon. It is cultivated in China for food, but was introduced in Europe, the United States, and during the 1970s in South Africa also, as a biological control agent for aquatic weed control. No indigenous fish species is as effective in the control of aquatic vegetation as the grass carp.
Grass carp have elongated, chubby, torpedo-shaped body forms. The terminal mouth is slightly oblique with non-fleshy, firm lips, and no barbels. The complete lateral line contains 40 to 42 scales. Broad, ridged, pharyngeal teeth are arranged in a 2,4 – 4,2 formula. The dorsal fin has eight to 10 soft rays, and the anal fin is set closer to the tail than most cyprinids. Body colour is dark olive, shading to brownish-yellow on the sides, with a white belly and large, slightly outlined scales.
A grown grass carp (Image:Wikipedia)
The grass carp grows very rapidly. Young fish stocked in the spring at 20 cm will reach over 45 cm by fall. The average length is about 60–100 cm. The maximum length is 1.4 m and the maximum weight 40 kg. According to one study, they live an average of five to 9 years, with the oldest surviving 11 years. They eat up to three times their own body weight daily. They thrive in small lakes and backwaters that provide an abundant supply of freshwater vegetation, preferring large, slow-flowing or standing water bodies with vegetation.
We are aware of the controversy over the introduction of exotic fish species into our local water bodies, and that the grass carp is amongst these species concerned. But, they are without a doubt one of the best fighting freshwater fish in our country, and a “greener option” as they:
- Eliminates vegetation cost effectively (cheaper than by herbicides or manually).
- Is safer and environmentally friendlier than control by chemicals and herbicides.
- These fish live long and control vegetation over many seasons.