B. Tharmini and M.D.S.T. de Croos
Department of Aquaculture and Fisheries, Faculty of Livestock, Fisheries & Nutrition, Wayamba University of Sri Lanka, Makandura, Gonawila (NWP), Sri Lanka
Seaweed Kappaphycus alvarezii, was recently introduced to Sri Lanka. But suitable culture methods; solutions for fish grazing; and suitable culture sites have not yet been investigated under native conditions. Thus, this study compared the growth of K. alvarezii under different culture methods and to find a method to minimise fish grazing as it reduces the harvest and contributes to further spreading. Growth rates of K. alvarezii were tested under 3 culture methods, “raft”; “line”; and “cylinder-cage” at two sites in northern Sri Lanka. Each of these methods consisted of three replicates. Around 60 seedlings, of a unit weight of 60-100g, were tightened into each raft and line, while inserted into cylinder cages. In 3-day intervals, 5-randomly selected seedlings were weighted & replaced from “line” and “raft”, while “cylinder-cage” was weighted as an entire unit, in determining the percentage growth rate & weight lost. Among the 3-culture methods, cylinder-nets resulted in the highest growth rates of K. alvarezii & highest economic profits (p<0.05). Mechanically damaged seaweed parts were remaining inside the cylinder net resulting in zero weight loss and further spreading. Cylinder nets can frequently be cleaned to avoid clotting due to their smaller size. The growth rate of K. alvarezii was redundant after 40 days thus, harvesting is recommended ~40th day of the culture cycle. At this stage, reproductive structures were not reached to its maturity hence spreading due to sexual reproduction was minimum.
A comprehensive study should be conducted in analyzing the associated environmental risks before popularizing K. alvarezii.