Litopenaeus vannamei is a major farmed shrimp species in the world

suffering serious losses because of hepatopancreas necrosis syndrome (HPNS) in recent years. The outbreak of HPNS is believed to be correlated with toxic chemical and physical factors as well as opportunistic pathogens. In 2015

we detected the concentration of ammonia

nitrite and nitrate nitrogen in 43 shrimp ponds of a aquaculture farm in Dianbai county

Guangdong province

China. In the first 22 days of breeding

the concentration of ammonia nitrogen ranged from 0.01 to 0.30 mg·L

-1

while nitrite nitrogen was below 0.01 mg·L

-1

. The concentration of nitrate nitrogen ranged from 0.01 to 0.60 mg·L

-1

with a similar tendency to that of ammonia nitrogen. During 22 to 72 days of breeding

the concentration of ammonia nitrogen increased from 0.30 mg·L

-1

to 1.50 mg·L

-1

in volatility. Unlike ammonia nitrogen

the nitrite nitrogen and nitrate nitrogen were generally stable

slowly and synchronously rising from 0.01 mg·L

-1

to 0.80 mg·L

-1

. After 72 days of breeding

their concentration all enhanced and fluctuated between 0.60 mg·L

-1

and 1.50 mg·L

-1

. Compared with the change of nitrite nitrogen

the sharp fluctuation of ammonia nitrogen was occurred about 26 days in advance. Moreover

we also detected the concentration of ammonia nitrogen after the zeolite and fertilizer were added in five shrimp ponds during breeding. The concentration of ammonia nitrogen was reduced by 19.50% at 1 day and reduced by 37.54% at 2 days after fertilizer addition. After adding zeolite powder

ammonia nitrogen was decreased by 47.62%，23.34%，60.73% and 76.58% in 4 days

respectively. Results also showed that the feed amount was positive correlated with the concentration of ammonia

nitrite and nitrate nitrogen (P

<

0.01). In summary

this study showed that the ammonia nitrogen was the limiting factor in closed culture of L. vannamei during the middle and late culture period

greatly influenced by climate. Besides

nitrite nitrogen was the restrictive factor

especially in the late culture period. Considering the tendency of ammonia nitrogen and nitrite nitrogen

the ecological system of closed shrimp culture mode can be divided into early ecosystem

medium ecosystem and late ecosystem.