Fairy Shrimp (Streptocephalus sirindhornae) as Live Feed Improve Growth and Carotenoid Contents of Giant Freshwater Prawn Macrobrachium rosenbergii

INTRODUCTION

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Fairy shrimp are microcrustaceans in the order Anostraca, usually appear in temporary pools or seasonally-flooded depressions. They are well-adapted to living in arid areas where water is present for only part of the year. Their eggs (or cysts) will survive drought for several years and hatch about 24 h after rains fill the pools where they live. Three species of fairy shrimp (Streptocephalus sirindhornae Sanoamuang, Murugan, Weekers and Dumont; Branchinella thailandensis Sanoamuang, Saengphan and Murugan; and Streptocephalus siamensis Sanoamuang and Saengphan) have been discovered from Thai freshwaters (Sanoamuang et al., 2000, 2002; Sanoamuang and Saengphan, 2006). Since then attempts have been made to culture these species in order to use them as new live feed for freshwater aquatic animals such as prawns, shrimp and ornamental fish (Saengphan et al., 2005, 2006; Sanoamuang et al., 2006; Boonmak et al., 2007; Plodsomboon and Sanoamuang, 2007; Sriputhorn and Sanoamuang, 2007; Saengphan and Sanoamuang, 2009). Cultures of S. sirindhornae and B. thailandensis can be done in circular outdoor, concrete ponds (diameter of 1 m, volume of water of 150 L) at an initial density of 50 nauplii L^-1 (Saengphan et al., 2006). Mass cultures of S. sirindhornae were also done successfully in rectangular, earthen ponds (1,600-3,200 m²) at an initial density of 1,250 individual’s m^-2 (Saengphan et al., 2006). Cyst production of S. sirindhornae and B. thailandensis under static conditions at room temperature (21-34°C) can be as high as 18,685 and 6,699 cysts female^-1, respectively (Boonmak et al., 2007). These species are characterized by high cyst hatchability (76-99%), short life spans (ca. 1 month), high fecundities and they are easy to culture (Saengphan et al., 2005, 2006). Furthermore, fairy shrimp cysts can be harvested easily for further use and storage. In addition, B. thailandensis was reported to contain a higher protein content of 64.9% (Saengphan et al., 2006) compared to 56.4% in Artemia sp. (Tunsutapanich et al., 1993). Velu et al. (2003) demonstrated that Streptocephalus dichotomus Baird had a high level of total carotenoids (114.3 μg g^-1 dry wt.) compared with that of a cladoceran Moina micrura (29.5 μg g^-1 dry wt.). Fairy shrimp are also cooked and consumed by local people in North-East Thailand (Sanoamuang and Dumont, 2000).

Freshwater prawn farming is an important industry in many Asian countries, which contributes to over 98% of the global freshwater prawn production (Asaduzzaman et al., 2009). The giant freshwater prawn, Macrobrachium rosenbergii (de Man), is one of the most popular prawn species used for commercial farming in Asia including Thailand (New, 2005; Thanh et al., 2009). In 2005, the production in Thailand was evaluated to be 30,000 t at a value of US$ 79,096,000 ranking third in producers behind China (99,111 t) and India (42,820 t; Schwantes et al., 2009). Prawn farming is concentrated along irrigation canals and mostly use formulated, protein-rich pellets, thus it requires frequent water exchange to maintain suitable water quality. One of the farming problems was the discharge of nutrient-rich effluent waters into public waterways, resulting in eutrophication and poor public water quality (Alam, 2007; Schwantes et al., 2009).

In order to reduce reliance on live feed Artemia spp. in aquaculture, researches have been conducted over the last decade to find an alternative to live feed (Gonzalez et al., 2008). The suitability of decapsulated cysts and adults of fairy shrimp Streptocephalus dichotomus as a sole diet was successfully introduced to ornamental angelfish Pterophyllum scalare larvae (Velu and Munuswamy, 2003), gold fish Carassius auratus, respectively (Velu and Munuswamy, 2007) and juvenile fish Oreochromis mossambicus (Prasath et al., 1994). Nauplii of S. proboscideus were used for larviculture of tilapia (Oreochromis aureus) by Ali and Dumont (1995) and Persian sturgeon (Acipenser persicus) by Namin et al. (2007). In this study, we used adult fairy shrimp, S. sirindhornae as a live food to test their suitability in enhancing growth and carotenoid contents in the giant freshwater prawn M. rosenbergii. This was an attempt to use their high nutritional value and to avoid water quality deterioration that is otherwise caused by pellet feeds.

MATERIALS AND METHODS

Experimental design and cultivation of prawns: The experiment was carried out at the Applied Taxonomic Research Center, Khon Kaen University, Khon Kaen Province, North-East Thailand, during 15 March and 14 May 2007. One-month old juveniles of giant freshwater prawn, Macrobrachium rosenbergii (mean initial wet weight 1.65 mg) obtained from a commercial hatchery in Suphan Buri Province, central Thailand were stocked at a density of 50 juveniles m^-2 in earthen ponds for 2 months. After that they were then reared at a density of 8 individuals m^¯2 until the age of 6 months. A locally formulated and prepared pellet diet (0.3-0.4 mm size) was provided as food, containing the following components: 35% protein, 45% carbohydrate, 3% fat, 2% vitamin/mineral, 4% ash, 12% moisture. The diet was fed at a rate of 3% of the prawn body weight (Chetawan et al., 2002) during acclimation and experimentation per day. Five prawn culture treatments were set up with 5 ratios of food concentrations for a period of 60 days. The food ratios of adult fairy shrimp to dry diet in the treatments were 0: 100, 25: 75, 50: 50, 75: 25 and 100: 0. The 6-month old prawns were randomly selected to culture individually in circular black plastic containers containing 20 L of freshwater. Each food concentration was experimented with 12 replicates and the whole experiment (5 treatments) using a total of 60 individual males. Only male prawns were used because the 6-month old females will produce mainly eggs instead of meat. During the experiment, specimens were subjected to the following conditions; water renewal rate of 50% on alternate days; photoperiod, 12 h light: 12 h dark; water temperature 30±6°C.

Culture of fairy shrimp: Cysts of fairy shrimp, Streptocephalus sirindhornae were obtained from the Applied Taxonomic Research Center. They were incubated in 3 L plastic containers with dechlorinated freshwater that was exchanged in 48 h intervals. One-day old nauplii were transferred to a 1,600 m² earthen pond with a volume of 960 m³ at a density of 1,250 individuals m^-2. To stimulate the production of natural algae to feed the fairy shrimp, 160 L of 7 day old Chlorella sp. were transferred into the pond together with 70 kg of dried chicken faeces and 10 kg of N-P-K (16- 20-0). Cultures of Chlorella sp. were performed using the procedure of Saengphan et al. (2005). After 25 days, adult fairy shrimp (2-3 cm long) were chosen to feed the prawns according to the experimental design.

Water quality measurements: Water quality variables and nutrients (Mean±SE) in culture containers of adult M. rosenbergii fed with 5 different food ratios for 60 days were measured shortly before the water exchange every other day. Water temperature, pH and Dissolved Oxygen (DO) were determined using a thermometer, WTW pH meter (model 3150l) and WTW Oxygen meter (model Oxl 3400l) (WTW, Weilheim, Germany). Total ammonia nitrogen and total nitrite and alkalinity were determined according to methods of Boyd and Tucker (1993) and American Public Health Association (1981). All physicochemical parameters were determined at 15.00 h every 5 days of the experiment.

Measurement of parameters: The experimental prawns were measured and individually weighted every 5 days for 60 days. Body length was measured with a Vernier caliper (to the nearest 0.1 mm) and weight was determined by a precision balance (to the nearest 0.1 mg) after removing excess water with tissue paper. Specific Growth Rate (SGR), Feed Conversion Ratio (FCR) and Survival Rate (SR) were evaluated during the 60-day trial. Performance was measured as a function of weight increase and by calculation of the following parameters:

where, W_t is the final weight (g), W_i is the initial weight and T is the duration of experiment (days).

Total carotenoid contents from the prawn meat were analyzed using high performance liquid chromatography (Rodriguez-Amaya and Kimura, 2004). Water quality analyses were done every 5 days according to procedures of the American Public Health Association (1981) standard methods.

Data analysis: Data were analyzed by analysis of variance (ANOVA), using the methods described by (Sokal and Rohlf, 1981). When significance was demonstrated, Duncan’s multiple range test (Duncan, 1955) was used to identify which means differed significantly from each other. Significance was declared at p = 0.05.