LARVICULTURE DEVELOPMENT FOR THE AFRICAN RIVER PRAWN Macrobrachium vollenhovenii

Eugene D. Blair*, Shawn D. Coyle and James H. Tidwell
 
Aquaculture Research Center
Kentucky State University
Frankfort, KY 40601
eugene.blair@kysu.edu

The African river prawn Macrobrachium vollenhovenii is a large decapod crustacean endemic to the west coast of Africa from the Senegal River to Angola.   Historically, the Senegal River basin supported an artisanal prawn fishery extending from the coast to more than 200 miles inland.  Due to its relatively large size (>100g) and high market value, M. vollenhovenii has been proposed as a candidate for commercial aquaculture in the region. The development of species specific larviculture technologies is the primary bottleneck to commercial production.  To date very little research has been done related to the propagation of this particular species.  Larval development in Palimonidae crustaceans is characteristically complicated by a relatively long hatchery phase where larvae undergo several stages of transformational development before reaching the post-larval stage when they are ready for freshwater.  Several attempts using established protocols for the commercially important Asian prawn M. rosenbergii have proven unsuccessful with survival to post-larvae consistently <1%.  

Initially, a series of static assays were conducted to provide basic information of optimal salinity and safe levels of ammonia for larviculture. The iso-osmotic salinity was estimated to be 16-18 ppt after a 5 day starvation test with freshly hatched stage one larvae where tested salinities ranged from 0-24 ppt. To determine safe levels of ammonia, a 96 h static ammonia assay was performed on stage one larvae.  The nominal concentrations tested ranged from 2 to 16 mg NH4/L.  Water temperature was maintained at 26oC by use of a single water bath and a submersible heater.  The salinity of the test water was 16 ppt and the pH was 8.3.  The 96 h LC50 value was calculated to be 7.4 mg/L.  These results suggest that M. vollenhovenii may require higher salinity and exhibits a lower tolerance to ammonia compared to M. rosenbergii. Over a two year period many trials were conducted using different feeding protocols with continued poor survival to PL in recirculating systems where ammonia concentrations routinely spiked to over 0.5 mg/L during the >90 day larval cycle.  A recent trial evaluated an outdoor "greenwater" system which resulted in 25% faster progression to stage 7; while maintaining ammonia concentrations <0.1 mg/L.  Greenwater systems may provide more efficient removal of nitrogenous waste compounds and may also provide a nutritional contribution through direct feeding on algae and/or continued enrichment of Artemia.