Uses of aquatic macrophytes for nutrient removal in a recirculation system for tropical fish culture
- Bangkok : Asian Institute of Technology, 2000
- 178 leaves
- Dissertation ; no. AQ-00-04 .
- Asian Institute of Technology. Dissertation ; no. AQ-00-04 .
A dissertation submitted in partial fulfillment of the requirements for the degree of Doctoral of Technical Science, School of Environment, Resources and Development
Thesis (Ph.D.) - Asian Institute of Technology, 2000
The objective of this thesis research is to assess the role and efficiency of aquatic plant on nutrient removal in a recirculation system for aquarium sh culture. A eld survey of commercial aquarium sh farms was conducted to better understand the water use in culture systems before setting up the experiments. A series of experiments was conducted on ammonia production by aquarium sh and nitrogen uptake rates by submerged and emergent aquatic plants. The results obtained from these experiments provided basic information to design a pilot-scale recirculation system, which efficiency in nutrient removal was then evaluated. Results show an inverse relationship between sh size (weight) and rate of total ammonia nitrogen (TAN) production in goldsh (Carassius auratus), angelsh (Pterohyllum scalare) and sailn molly (Poecilia latzpinna). TAN production of these sh are expressed in these equations: (a) goldsh: TAN= 63.88W°"2, (b) angelsh: 2"/nv= 25.20 W°2° and (C) Sailn molly: TAN = 39.32W°'2. The hourly rates of ammonia production by these sh reached the peak 4 hours after feeding. Fecal nitrogen production rate was also related to sh size. TAN released from fish feed increased to 0.53 mg/g dw/d. Six species of common aquarium plants were tested for their efficiency (rate) in uptake of ammonium and nitrate as nitrogen nutrient sources. Among submerged plants, water wisteria (Hygrophila diormis) showed the greatest uptake of NH4-N and NO;-N at the rate of 7.58: 0.23 and 3.38i0.05 mg N/ g dw/d, respectively; followed by giant vallis (Vallisnaria giganlea) and ambulia (Limnophila heterophylla). Among emergent plants, dwarf bacopa (Bacopa mormieri) showed the greatest uptake of NI-14-N and NO;-N at the rate of 4.82i0. I3 and 3.29: 0.44 mg N/ g dw/d, respectively; followed by sword plant (Echinodorus cordifolius) and red ludwigia (Ludwigia regens). Nitrogen uptake rate by water wisteria and dwarf bacopa also varied with light intensity at 3,500, 7,000 and 10,500 lux. The nitrogen uptake rate of water Wisteria at 3,500 and 7,000 lux was signicantly higher than that at 10,500 lux, and the rate for dwarf bacopa at 7,000 and 10,500 lux was signicantly higher than that at 3,500 lux. In the presence of various nitrogen and phosphorus concentrations under natural lighting, the optimal N/P ratio is 5 for water Wisteria and IO-20 for dwarf bacopa. Wastewater from aquarium sh (goldsh) tanks was supplied to 2 species of aquatic plant (water wisteria and dwarf bacopa) with spray and sand substrate in a small-scale recirculation system. There was no signicant difference among all treatments for goldsh growth performance. The FCR of goldsh in the sand system was signicantly lower than that in the spray system. The growth performance of aquatic plants in the sand system was signicantly (P<0.05) better than in the spray system. The results of the pilot scale recirculation system show that important water quality parameters for sh culture could be maintained in optimal conditions. This was demonstrated by the successful removal of TAN and NO;-N at low levels by the aquatic plant (water wisteria) treatment. During the 12-week experimental period, goldsh grew from 4.531-0.11 g at stocking to 103810.30 g at harvest, with an average daily weight gain of 0.071001 g/day. The average total weight of goldsh was 867 29140.27 g/tank (1.54 m2), ranging from 815.2 to 946.5 g/tank. The average survival rate of goldsh was 91 % and feed conversion ratio was 2.7. The goldsh-aquatic plant recirculation system provides an effective means in maintaining water quality and reducing amount of water requirement for aquarium sh production. However, the results of this study showed that there was poor growth performance of aquatic plant. This was probably due to the low light intensities (530-4,080 lux) during daytime of study period and imbalance of N/P ratio according to pl-I level of water (7.6-8.2) that resulted to phosphorus precipitation. Therefore, using sh-aquatic plant system for commercial production in future, environmental conditions for plant growth e.g. nutrient supplementary, light condition temperature and culture season, etc. have to be considered.