Monday, December 20, 2010

Letter to Wild Life Warden



Kariavattom, Thiruvananthapuram – 695581, Kerala

Ph: 0471 2167679; 094472 16157 (mob); E mail:


08 December 2010

Dr. A. Biju Kumar

Assistant Professor




The Chief Wildlife Warden,

Kerala Forests & Wildlife Department,

Forest Headquarters,





The proposal by the Fisheries Department to stock fish seeds in reservoirs as per the project sanctioned to them by the Government of India, would hamper the indigenous biodiversity in various manners. A note on the impacts of introduction of exotic species in water bodies is attached below for your kind perusal.

  1. Invasive species are considered to be a significant threat to biodiversity, often categorised next to habitat destruction, especially in freshwater systems. Non-native, invasive fish have contributed to the extirpation of indigenous species. There are already well established documents on the ecosystem level and species level catastrophic impacts of exotic species introductions, which we also have to take into account very seriously.


  1. The present case of introduction of Indian Major Carps (IMCs) should also be discussed in a holistic ecosystem perspective, as there are reports that introduction of fish to different habitats within the country may also lead to loss of biodiversity. Though there are such reports in Asia (Kottelat and Whitten, 1998), such studies, unfortunately, have not initiated in India. This demand for a precautionary approach.
  2. The rivers of the Western Ghats are freshwater biodiversity hotspots, as each stream may serve as an evolutionary centre as far as highly endemic freshwater fish fauna are concerned. The water bodies associated with the Western Ghats harbours 288 species of freshwater fish of which 118 are endemic. A larger diversity of new freshwater fishes has been recorded from the aquatic ecosystems associated with the Kerala part of the Western Ghats. For example, a relatively small watershed of Chalakkudy river, covering less than 1700sq km has more than 100 species of fishes, many of which are endemic to the river! Moreover, the upper reaches of most of the river basins in Kerala are within forests and have not been exhaustively surveyed for their biota. 
  3. Majority of the endemic fishes in Kerala find their home in the pristine streams and rivers within the reserve forests of Kerala. The recent recording of Piranha from Chalakkudy river, African catfishes from many water bodies including Periyar lake and Nile tilapia from Bhrathapuzha river is a matter of concern to the freshwater aquatic diversity, taking into account the greater endemism of fish fauna in these systems. Yet we are trying exotic fishes continuously. With the ongoing aquaculture and aquarium trade initiatives, many more may find their way to the aquatic ecosystems.
  4. The flying barb (Esomus thermoicos), Crossocheilus periyarensis, Gonoproktopterus micropogon periyarensis, Labeo dussumieri, Lepidopygopsis typus, Neolissochilus wynaadensis, Osteobrama bakeri, Osteochilus (= Kantaka) brevidorsalis, O. longidorsalis, Puntius arulius arulius, Puntius exclamatio, Puntius pookodensis, P. puckelli, P. denisonii, P. chalakkudiensis, P. ophicephalus, Garra hughi, G. menoni, G. surendranathani, G. periyarensis, Homaloptera menoni, H. pillaii, Travancoria jonesi, T. elongate, Mesonemaheilus  menoni, M. remadevii, Nemacheilus deninsoni pambaensis, N. sinuatus, Oreonectes keralensis, Pangio bashai, Batasio travancoria, Horabagrus nigricollaris, Mystus armatus, Pseudeutropius mitchelli, Glyptothorax anamalaiensis, G. housei, Clarias dayi, Horaglanis krishnai, H. alikunhi, Microphis brachyurus, Monopterus (Amphipnous) fossorius, M. (Monopterus) eapeni, M. digressus, M. roseni, Parambassis dayi, Pristolepis marginata, Pristolepis malabaricus, Channa diplogramma, C. leucopunctatus, Macrognathus guentheri, Carinotetraodon imitator are some of the species endemic to Kerala part of the western ghats, and majority of them are restricted in their distribution to the Western Ghats rivers. Moreover, it is also important to note that all the fishes reported new to science from Kerala in the recent past have their restricted distribution in the western ghat rivers. In this context, introduction of more competitive and fast growing IMCs to the reservoirs would lead to their migration both upstream and downstream, hampering the habitats and the very existence of indigenous species. The record of IMCs from the river systems of Kerala are all escapes from the reservoirs.


  1. One of the possible impacts of IMCs in our rivers, especially in the upstream reservoirs, may be habitat alteration and replacement of indigenous species through competition for food and space. The IMCs are represented by three species: Catla (Catla catla), Rohu (Labeo rohita) and the mrigal (Cirrhinus cirrhosus; earlier Cirrhinus mrigala). Catla catla grows to a maximum length of 182 cm and a weight of over 38 kg and is a surface and mid-water feeders, feeding mainly omnivorous with juveniles feeding on aquatic and terrestrial insects, detritus and phytoplankton. The column feeder Labeo rohita attains a maximum length of 200 cm and weight of 45 kg, and prefers plants as their food. The mrigal Cirrhinus cirrhosus grows to 100 cm in size and 13 kg in weight and is a bottom feeder. It is important to note that majority of indigenous fish in the Western Ghats never attain this length, and feeds as voraciously as IMCs. Further, by exploiting all the available niche, they are strong competitors.


  1. Therefore, we also need to consider the fact the smaller rivers in Kerala are ecologically not suitable for the IMCs and in the long run, culturing them in the reservoirs of Kerala would not be economically feasible in the long run, as the current motive of stocking is ONLY to 'enhance' fish production.
  2. Exotic fishes such as Tilapia (Oreochromis mossambicus), Common carp (Cyprinus carpio), African catfish (Clarias gariepienus),  and IMCs have gained entry into the reservoir ecosystems of India through accidental or deliberate introduction. Among them tilapia has already entered into all the upstream rivers of Kerala, including forest streams and established viable populations. A recent study by Mr Robin Kurian Abraham shows that in Kulathupuzha river Common carp is in the process of replacing the threatened mahseer fish and is now occupying majority of the niches. This is an indication of possible replacement of indigenous fish by the larger and highly competitive carps. 
  3. Convention on Biological Diversity states: "Inland water ecosystems are particularly vulnerable to invasive alien species. There is limited success in the prevention, eradication and control of invasive alien species in inland water ecosystems with fewer methods available than for the control of invasive species in terrestrial systems, particularly for organisms, which are submerged (such as fish)".
  4. The costs and benefits of invasive alien species are mixed because alien species are often a major source of income, food or livelihood for local communities and often support major economic activities (such as aquaculture production).  But at the same time, invasive alien species may degrade the natural resources upon which economies and local communities depend. These mixed benefits and risks are difficult to predict or manage which results in potential conflicts regarding the use of invasive alien species. The challenge, therefore, is how to maximize the benefits whilst minimising the risks. All too often, alien species are used as an easy option for agriculture and fisheries related activities.  Greater attention needs to be given, where feasible, to promoting the use of native species. However, the use of native species should include precautions to conserve the genetic diversity of native populations. In this context conservation of indigenous biodiversity should be given priority.
  5. In this context, economic viability of the project of introduction of IMCs in the reservoirs inside reserve forests also needs to be assessed. As opined by Dr. Sathis Chandran, "we have little data on the primary as well as secondary productivity in our reservoirs and the carrying capacity of these unstable water bodies to support large fish populations is to be questioned". For example, the tilapia, O. mossambicus was first introduced into the pond ecosystem of the country in 1952 and soon it was stocked in the reservoirs of south India. By the end of 1960s, most of the reservoirs in Tamil Nadu and those in the Palakkad and Thrissur districts of Kerala were regularly stocked with tilapia. Performance of tilapia in ponds of south India has been discouraging mainly due to its early maturity, continuous breeding, over-population and dwarfing and this may be expected in reservoirs also. The unfortunate situation is that we don't have strong data base even now on the ecology and food web dynamics of many of the threatened indigenous fishes, and the attention of researches should be focussed on this.
  6. Considering the possible negative impacts of IMCs to the indigenous fish fauna, which shows greater endemism, the move to stock them in the reservoirs within the reserve forests need to be stopped as a precautionary principle.


08 December 2010                                                                              BIJUKUMAR












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