Effects of Nitrogen Sources on the Growth and Biochemical Composition of Diatom (Amphora coffeaeformis) Used for Shrimp Larviculture

Abstract

Amphora coffeaeformis is a benthic diatom and serves as a rich nutritional feed for various aquaculture industries. The objective of this experiment was to compare the effects of different nitrogen sources on the growth and biochemical composition of the diatom (A. coffeaeformis) culture. Sodium nitrate in Guillard’s f medium, used as a control treatment, was compared with sodium nitrite and ammonium sulfate. The results in the 3rd batch of culture showed that all treatments led to the highest growth on Day 6. The highest cell dry weight occurred in the ammonium sulfate treatment with significance (0.78±0.06 mg/mL). The cultures in each treatment were harvested at the exponential phase (Day 3) for biochemical composition analysis. A. coffeaeformis in the ammonium sulfate treatment significantly accumulated the highest protein content, at 44.82 % by dry weight, while the highest lipid content at 29.78 % by dry weight was significantly found in the sodium nitrate treatment. The cell size and structure showed no significant differences among the treatments. The experiment demonstrated the effects of different nitrogen sources on the growth and biochemical composition of A. coffeaeformis. After that, we selected A. coffeaeformis that was cultured with the nitrate and ammonia nitrogen sources for feeding to shrimp larvae. This experiment was conducted to evaluate the effects of A. coffeaeformis on the growth, survival rate, salinity stress test, and ammonia stress test for shrimp. The experiment was designed with four treatments, as follows: 1) the control feed with flake winner (no water exchange for 28 days), 2) Am-NO3 supplement with A. coffeaeformis cultured using nitrates (no water exchange for 28 days), 3) Am-NH3 supplement with A. coffeaeformis cultured using ammonia (no water exchange for 28 days), and 4) the positive control feed with flake winner (daily water exchange at 20 %). The results showed that the growth of shrimp fed with the diet supplemented with A. coffeaeformis cultured using nitrate and ammonia were not significantly different from the negative and positive controls (P > 0.05). However, the survival rate in the negative control was significantly lower than the other groups (P < 0.05). In this study, the stress test for white shrimp postlarvae utilized 2 methods: the ammonia or salinity stress tests. The survival rate of the shrimp after the ammonia stress test was not statistically and significantly different (P > 0.05). However, the results from the salinity stress test indicated that the highest survival rate was observed in the shrimp fed with the diet supplemented with A. coffeaeformis cultured using nitrate. A. coffeaeformis cultured with the sodium nitrate treatment had a positive effect on shrimp tolerance to salinity changes.