Effects of frequency and amplitude of salinity fluctuation on the growth and energy budget of juvenile Litopenaeus vannamei (Boone)

The effects of salinity fluctuation on the growth, intermoult period and energy budget of juvenile Litopenaeus vannamei were investigated. Salinity fluctuation regimes were set in different frequencies of 2, 4 and 8 days and different amplitudes of +/- 2, +/- 5 and +/- 10 g L(-1) from a control salinity of 20 g L(-1). After a 48-day feeding trial, the intermoult period of shrimp became shorter with increasing amplitude and frequency of salinity fluctuation (P < 0.05). Both the frequency and the amplitude of salinity fluctuation had a significant effect on the growth rate of L. vannamei juveniles (P < 0.05). At the frequency of 4 days, the highest growth rates occurred at amplitudes of 5-10 g L(-1), whereas the growth rate was the lowest at 10 g L(-1) when the frequency was reduced to 2 days. Feed intake (FI) and assimilation efficiency (AE) of shrimp were also significantly affected by the salinity fluctuation (P < 0.05) and matched the growth rate response. The energy expenditures for growth (G), respiration (R), excretion (U) and exuviae (E) to the energy consumed as food (C) were not affected by salinity fluctuation. However, salinity fluctuation significantly affected the percentage of C as faeces (F), with the lowest value occurring at salinity amplitudes of 5-10 g L(-1) and frequencies of 4-8 days. Therefore, salinity fluctuations (every 4 days by +/- 5-10 g L(-1)) result in higher growth rates than constant salinity conditions (20 g L(-1)) through greater FI, enhanced feed assimilation and reduced faecal energy loss.