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MANAGEMENT OF RACEWAYS TO IMPROVE PRODUCTIVE RESULTS IN WHITE SHRIMP
Sebastian Arias Juan Portal Nicovita Technical Assistant Nicovita Technical Manager Alicorp Ecuador S.A. Alicorp S.A.A.
Despite the significant progress achieved by genetic programs in obtaining specific pathogen-free or specific pathogen-resistant (SPF or SPR) animals to combat problems caused by the white spot syndrome virus (WSSV), mortality rates are still high in production farms and they increase during low-temperature seasons, thereby affecting production and resulting in losses of up to 40%. In this connection, raceways –which are used to better plan stocking, reduce time in grow-out ponds and optimize food delivery during the postlarvae periods due to increased knowledge of the stocked population– could also be used to make thermal treatments which enable the mitigation of the effects of pathogens. Thermal Treatment to counter white spot As part of the treatment against WSSV, since 2005 Thailand has applied treatments involving increased temperature in larvae laboratories and in the raceways of shrimp trawlers, prior to stocking of shrimp into ponds. This methodology has been recently adopted by several producers in Ecuador and Peru, who have achieved promising results. The treatment in raceways used in Asia entails subjecting larvae to 32 ± 1 °C temperatures over a period of at least seven consecutive days (Wongmaneeprateep et al., 2010). As a result, hemocyte concentration would significantly increase in the hemolymph, with the consequent enhancement of defense mechanisms which would “clean” the virus larva (Sonnenholzner et al., 2002
a and Sonnenholzner et al., 2002
b).
During the first year of application of the technique in farms located in the province of Guayas - Ecuador, improvements were immediately apparent, with an increase of 32% in productivity, 20% in survival and 15% in weekly growth. For the second year of application of the technique, productivity increased again by 9 %, and survival and weekly growth by 7 %. Gustavo León, from the company Ecoacuícola located in Piura - Peru, stated that they started to apply this technique in 2012. They kept postlarvae at densities of 40 PL/L, at 32 °C and 1% salinity during nine days, achieving individuals of 0.01 to 0.015 gr with survival rates in the range of 85 to 90%. Thus, the target weight of 1 gr during nursery was attained at 25 days of culture (with densities of 600-1000 individuals/m
2); before that, this target was attained at 40 or
45 days. In the case of Ecuadorian shrimp trawlers, the procedure used is as follows: The raceways and the aeration and heating systems are disinfected with chlorine, rinsed with salt water and dried. Prior to larva arrival, the tanks are filled up to 50% of their operating level (Figure 1A); they are applied probiotic bacteria and aeration at 50% of their capacity. Finally, the diatom algae are inoculated.
Figure 1.- A) Raceway for shrimp nursery in Ecuador. B) Diesel water heaters.
It is recommended that the postlarvae be received in the PL11 or PL12 stage at air temperature (25° C during the cold season or 28° C during the warm season) with 34 – 35% salinity. Once the larva has acclimatized, the tanks are covered and temperature starts to increase through the use of diesel heaters (Figure 1B). Thermal treatment lasts between 10 and 14 days (Figure 2).
Figure 2.- Water temperature and salinity during thermal treatment of postlarvae in raceways in Ecuador. Between the third and fourth days of culture, 100% water level and 25% salinity must be achieved by using fresh and salt water. Next, changes are made exclusively with salt water so that 35% salinity is reached at the end of the nursery period (Figure 3). The daily change rate is between 10 and 20% according to monitoring of non-ionized ammonia (NH3), which must be kept below 0.30 mg/L. Two days prior to harvest, tanks are uncovered, the use of tempered water is disabled and water changes are made at air temperature, thus achieving 48-hour acclimation periods. Diet is based on NICOVITA nursery feed with 40% protein content (PC 40%) throughout the culture stage and is supplied in 8 daily doses. The weight obtained at 15 or 20 days of culture will depend on larva weight (PL/g) and initial density (PL/L).
Tem
pera
ture
(ºC
)
Salin
ity (
‰)
Culture time (day) Temperature
Table 1 shows growth for 20 days of culture with an initial weight of 250 and 300 PL/g and a density of 30 PL/L. For densities of 18 and 25 PL/L, results of up to 5 PL/g have been reported in culture periods of 15 days.
Day
Initial weight (PL/g)
250 300
1 250 300
2 210 290
3 170 275
4 140 250
5 110 200
6 82 170
7 70 138
8 64 127
9 52 100
10 40 70
11 31 60
12 25 58
13 20 45
14 15 32
15 14 32
16 12 25
17 9 25
18 11 20
19 10 14
20 8 12
Table 1.- Evolution of postlarvae growth with two different initial weights (expressed in
PL/g) and a density of 30 PL/L. Using this methodology, between 2011 and 2012, the average results shown in Table 2 and larvae with excellent appearance were obtained (Figure 4).
Culture parameter
Initial density (PL/L)
30 20
Culture days 20 15
Survival (%) 85 88
Weight (PL/g) 10 6
FCA 1,18 1,07
Table 2.- Average nursery results in Ecuador between 2011 and 2012.
Figure 3.- Shrimp postlarvae at the end of nursery with thermal treatment. BIBLIOGRAPHY Sonnenholzner, S., J. Rodriguez y J. Calderón. 2002
a. Temperature and WSSV: CENAIM
Studies Promising Shrimp Culture Technique. Global Aquaculture Alliance, Agosto: 55-57.
Sonnenholzner, S., J. Rodriguez, F. Pérez, I. Beatancourt, F. Echeverría, y J. Calderón. 2002b.
Supervivencia y respuesta inmune de camarones juveniles Litopenaeus vannamei desafiados por vía oral a WSSV a diferentes temperaturas. Boletín el Mundo Acuícola, 8(1): 50-56. Wongmaneeprateep, S., N. Chuchird, P. Baoprasertkul, P. Prompamorn, K. Thongkao y C. Limsuwan. 2010. Effects of high water temperature on the elimination of white spot syndrome virus in juveniles of Litopenaeus vannamei. Kasetsart University Fisheries Research Bulletin, 34(2):14-26.
Editors: Carlos Ching [email protected]; Máximo Quispe [email protected]; Juan Enrique Rosales [email protected]; Carlos Espinoza [email protected]
