World Aquaculture December 2020

WWW.WA S.ORG • WORLD AQUACULTURE • DECEMBER 2020 67 crayfish and Nile tilapia (Figs. 1 and 2), compared to red claw crayfish monoculture. The study was carried out at the National Center for Aquaculture Development (CENADAC, 27° 32’ S, 58° 30’ W). Five earthen ponds of 300 m 2 each were used, two for polyculture and three for red clawmonoculture (Fig. 3). The culture period was about four months (117 d), from February to May, in a semi-intensive systemwithout water exchange. Only water losses from evaporation and seepage were replenished. Before stocking, ponds were fertilized with poultry manure (400 kg/ha) and inorganic fertilizer, urea and triple superphosphate at 1.5 to 5 kg/ha (Boyd 1998). Stocking densities were 0.82 tilapia/m 2 and 1.50 red claw/m 2 for polyculture and 1.50 red claw/m 2 for monoculture. Initial species weight was 29 ± 8 g for tilapia, 1.5 ± 0.8 g for red claw used in polyculture, and 1.2 ± 0.7 g for monoculture. Experimental pelleted feed was made at CENADAC with a formula that was used in previous studies with pacú (Wicki and Luchini 2004) and tilapia in cages (Martin et al . 2007). The ingredients and chemical composition of the diet is showed in Table 1. In the polyculture system, only fish were fed daily after water quality testing. Feeding rate varied according to body weight, and was 5.0 percent at the beginning, decreasing month by month to 4.0, 2.7, 2.5 and 2.1 percent, respectively until the end of the study. For crayfish monoculture, the feeding rate was the same as used previously (Wicki et al . 2008), 20 percent at the beginning, decreasing to 12, 6, 5 and 4.2 percent at the end. Crayfish were fed every two days to decrease the feed conversion ratio. Ten percent of initial population of fish and crayfish were sampled monthly to determine growth and recalculate feeding rate. A quaculture in Argentina has developed slowly due to factors like high operating costs and strong competition for resources with traditional agricultural and livestock production. Pacú Piaractus mesopotamicus is the main species produced in aquaculture in Argentina, with average annual production of about 1,800 t/ha. This yield is produced under semi-intensive culture in the northern region. Culturing two species in the same environment maximizes space utilization and makes the most efficient use of ecological resources (Silva et al . 2006). Thus, polyculture could be a productive choice to promote sustainable aquaculture. Red claw crayfish Cherax quadricarinatus was introduced into Argentina fromAustralia in the early 1990s and Nile tilapia Oreochromis niloticus was introduced fromBrazil and Paraguay in the 1980s, both to develop a domestic market. Red claw crayfish yields from semi-intensive culture systems are 600-800 kg/ha (Wicki et al . 2008), but with low profit for farmers. Tilapia cultured in the same system and area can be marketed to tourists and Asian consumers. Both species in this culture system have not resulted in a productive success. Previous polyculture experiences in the same geographical area combining giant freshwater prawn Macrobrachium rosembergii and pacú (Wicki et al. 1998) showed a yield feasibility of 700 kg/ ha for prawn production with feeding only the fish. As tilapia is an herbivorous feeder and red claw a detritivorous feeder and both species share a similar thermal tolerance range, polyculture could be a key to solve pond underutilization and encourage production. Study Materials andMethods An exploratory research project was undertaken with the objective to investigate feasibility of integrated culture of red claw Improvement of Red Claw Crayfish Production in Northern Argentina by Polyculture with Nile Tilapia Gustavo Wicki and Rolando Hernández ( C O N T I N U E D O N P A G E 6 8 ) FIGURE 1. Red claw crayfish Cherax quadricarinatus at CENADAC. FIGURE 2. Nile tilapia Oreochromis niloticus at CENADAC.