Culture-based fisheries in non-perennial reservoirs in Sri Lanka: production and relative performance of stocked species

In Sri Lanka, there is a great potential for the development of culture-based fisheries because of the availability of around 12 000 non-perennial reservoirs in the dry zone (<187 cm annual rainfall) of the island. These reservoirs fill during the north-east monsoonal period in October to December and almost completely dry up during August to October. As these non-perennial reservoirs are highly productive, hatchery-reared fish fingerlings can be stocked to develop culture-based fisheries during the water retention period of 7–9 months. The present study was conducted in 32 non-perennial reservoirs in five administrative districts in Sri Lanka. These reservoirs were stocked with fingerlings of Indian (catla <i>Catla catla</i> Hamilton and rohu <i>Labeo rohita</i> Hamilton) and Chinese (bighead carp <i>Aristichthys nobilis</i> Richardson) major carps, common carp Cyprinus carpio L., genetically improved farmed tilapia (GIFT) strain of Nile tilapia, <i>Oreochromis niloticus</i> (L.) and post-larvae of giant freshwater prawn, <i>Macrobrachium rosenbergii</i> De Man, at three different species combinations and overall stocking densities (SD) ranging from 218 to 3902 fingerlings ha⁻¹, during the 2002–2003 culture cycle. Of the 32 reservoirs stocked, reliable data on harvest were obtained from 25 reservoirs. Fish yield ranged from 53 to 1801 kg ha⁻¹ and the yields of non-perennial reservoirs in southern region were significantly (<i>P </i>< 0.05) higher than those in the northern region. Naturally-recruited snakehead species contributed the catches in northern reservoirs. Fish yield was curvilinearly related to reservoir area (<i>P</i> < 0.05), and a negative second order relationship was evident between SD and yield (<i>P</i> < 0.05). Chlorophyll-a and fish yield exhibited a positive second order relationship (<i>P</i> < 0.01). Bighead carp yield impacted positively on the total yield (<i>P</i> < 0.05), whereas snakehead yield impact was negative. Bighead carp, common carp and rohu appear suitable for poly-culture in non-perennial reservoirs. GIFT strain<i> O. niloticus</i> had the lowest specific growth rate among stocked species and freshwater prawn had a low return.<br />