Abstract
àChapter 2, explored the links between water quality parameters, different types of food resources available, fish diet composition and fish growth/production. Common carp increased bioavailable nitrogen and phosphorus, a process that was enhanced by the addition of artificial feed. The effects of common carp were more pronounced in treatments with 0.5 than 1 common carp m -2 . PO 4 -P concentration was strongly correlated with phytoplankton and zooplankton biomass. One of the major findings was that rohu growth was best explained by natural food intake, while common carp growth was best explained by artificial feed addition and negatively correlated with natural food ingestion. Results indicated that common carp benefited directly from artificial feed addition while rohu benefited indirectly from the boost in natural food availability triggered by the fertilizing effect of the artificial feed.
àIn Chapter 3, the effects of different densities of common carp (0, 0.5 and 1 individual m -2 ) on natural food availability, natural food ingestion uptake and fish growth were compared under fed and unfed conditions. Stocking 0.5 common carp m -2 resulted in the highest observed natural food availability, the highest natural food ingestion, the highest fish growth (rohu: 1.55% body weight day -1 , common carp: 1.59) and the highest total fish production (3,532 kg ha -1 137 day -1 ). The effects were less pronounced when stocking 1 common carp m -2 . Rohu shifted from phytoplankton to zooplankton when the latter became more available in response to artificial feed addition.
àChapter 4 investigated the effects of common carp and artificial feed addition on water quality parameters and on the accumulation of nutrient in different types of natural foods present in the ponds. In all treatments all water quality parameters remained favourable for fish growth. The overall nitrogen and phosphorus concentrations were highest in treatments with 0.5 common carp m -2 followed by treatments with 1 and 0 common carp m -2 , respectively. The oxygen concentration decreased with increasing common carp density. More nitrogen and phosphorus accumulated in fish, phytoplankton and zooplankton in treatments with 0.5 common carp m -2 , followed by treatments with 1 and 0 common carp m -2 , respectively. The nitrogen and phosphorus accumulation in sediment was lower in presence of common carp than in the common carp free treatments. Concentrations of all nitrogenous and phosphorus compounds were higher in fed than in non-fed ponds except for NO 2 -N. A larger fraction of the input nutrients accumulated in all natural food types in non-fed than fed pond whereas the opposite were observed for the fraction of nutrients accumulating in the sediment.
· In the third part of this study (Chapter 5) the resting, grazing, swimming and social interactions of rohu and common carp were observed in purpose build tanks for the same treatments as applied in part 2. Rohu decreased intra-species and increased inter-species interactions with increasing common carp density. Presence of common carp reduced the resting time and increased swimming and grazing time of rohu near the tanks bottom. Rohu benefited from spending more time close to the bottom and wall in presence of common carp by ingesting more zooplankton, as in these areas zooplankton biomass was higher than in other parts of the tanks.
A general discussion of the experimental results is given in Chapter 6. Both addition of common carp and artificial feed affected the pond ecology, fish growth, total production and fish behaviour. Stocking 0.5 common carp m -2 was better than stocking 1 m -2 . The strength of this study is that it looked at the combined effects of stocking benthivorous fishes and feed addition considering water quality, natural food availability, feed intake and behaviour. Results show that behavioural observations are equally important as water quality and feed intake monitoring to explain synergism in polyculture. Similar studies, adding a third species, are recommended to further elucidate changes in the food web dynamics when synergism is observed in polyculture ponds.
Original language | English |
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Qualification | Doctor of Philosophy |
Awarding Institution |
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Supervisors/Advisors |
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Award date | 14 Jun 2006 |
Place of Publication | [S.l. ] |
Print ISBNs | 9789085044475 |
DOIs | |
Publication status | Published - 14 Jun 2006 |
Keywords
- carp
- labeo
- food webs
- fish ponds
- nutrients
- fish culture
- aquaculture
- fish production
- ecology
- water quality
- feeds
- animal behaviour
- ponds
- bangladesh