关键词:
amylases body condition
carcass composition
chemical composition
chloridesdiets electrical conductivity
environmental factors
enzyme activity
feed conversion efficiency
fish feeding
glycogen growth rate
liver liveweight gain
mus cles nitrate nutrition physiology
proteinases salinity
摘要:
To investigate the effect of inland groundwater salinity on growth performance, feed conversion efficiency, nutrient retention and intestinal enzyme activity in milkfish, two experiments were conducted. In the first experiment (Expt I), a 100-day monoculture of Chanos chanos [mean body weight (BW): 2.2 g] at different salinities (0, 10, 15, 20 and 25 parts per thousand) was carried out in ponds fertilized with cowdung (about 10 000 kg ha(-1) year(-1)) and poultry droppings (about 3000 kg ha(-1) year(-1)). The fish were fed a compounded supplementary diet (containing 40% protein) at 5% BW day(-1). Studies have revealed that growth increased with each increase in the salinity level;the highest values in weight gain and energy assimilated were observed in ponds maintained at 25 parts per thousand salinity [weight: 322.2 g and specific growth rate (SGR): 8.3]. Highest values of condition factor (0.7) and exponential value (n) of the length-weight relationship (LWR;n = 3.25) were also observed in ponds maintained at 25 parts per thousand salinity. Dissolved oxygen (DO), biological oxygen demand (BOD), pH and nutrient release remained at the optimal level during the culture period. High values of chlorophyll a, net primary productivity (NPP), phytoplankton and zooplankton population coincided with the highest values of alkalinity and turbidity in ponds maintained at 25 parts per thousand salinity. Multivariate analysis revealed a significant positive correlation of chlorides (r = 0.91), conductivity (r = 0.89) and hardness (r = 0.96) with fish growth. Productivity indicating parameters viz. NPP (r = 0.45), nitrate (r = 0.94) and o-PO4 (r = 0.52) also showed a significant positive correlation with fish weight gain. In the second experiment (Expt II), milkfish (mean BW: 3.7 g) fry were exposed to different levels of salinity (0.0, 10, 15, 20, 25 and 30 parts per thousand), and maintained for 90 days in the laboratory. Significantly (P < 0.05) high growth (percentage increas