344 research outputs found
Feeds and feeding strategies for Colossoma macropomum (Cuvier 1818) fish growth as related to dietary protein.
No full textColossoma macropomum is an indigenous fish species from the Amazon region. The amino acid profile of its body protein proved to be similar to that of other fish species. Soya meal and fish meal have, based on their amino acid profiles, a comparable protein quality. This hypothesis was confirmed in a feeding trial. As soya meal is less palatable than fish meal, more soya in the diet tends to decrease feed uptake and growth rate, but increases protein utilization efficiency. Growth of C. macropomum is fast and requires a dietary protein content of approximately 43%. Fish growing at maximal speed displayed a protein utilization efficiency of only 50% of the maximal possible efficiency. In ad libitum fed C macropomum 20 - 30% of the feed remains uneaten. In spite of this wasted feed, the feed uptake/weight gain ratio ranged between 0.57 and 0.71 with a high quality feed. Increasing the feeding frequency from one to five meals per day increased feed uptake and growth. Fish displayed a clear daily bio-rhythm with maximal feed uptake in the late afternoon. Lipid addition to the diet increased the protein utilization efficiency less than reported for salmon. An increased dietary protein content increased the body protein content and decreased the body lipid content. Adaptation of the size of the internal organs to the characteristics of the diet is possibly the cause that diet composition affects the body composition of fish. Accumulated data were analyzed by an empirical and an explanatory model. Both methods identified protein ration as the major variable determining fish growth. In describing the data, the average errors of both methods were similar. However, the empirical model produced more outlying values. It was concluded that the explanatory model with some minor improvements can be turned into a useful tool for research and practical management. Fast growth and a flexible body composition make C. macropomum a suitable study object for the development of improved fish growth models
Microalgae-bacteria interactions: a key for improving water quality in recirculating aquaculture systems?
No full textThe roles of algae in improving aquaculture water quality are well-established. However, the integration of algae in a recirculating aquaculture systems (RAS) is less popular mainly due to the large area required for photosynthesis. As science progresses, a growing number of reports are available on the benefits of algae to water quality and fish health. This motivated the author to investigate the effects of algae on a RAS stability, by measuring the water quality and the effects on bacterial community composition in a RAS. A review was conducted on nitrogen removal by algae and the operation of an algae reactor in a RAS. This showed that a RAS configuration influence algae performance by affecting nitrogen loading and nitrogen species (ammonium versus nitrate), cultivation methods (suspended versus attached) and environmental conditions (light, temperature, pH, oxygen, and carbon dioxide). Next, a periphytic microalga, Stigeoclonium nanum was cultured in suspension or immobilized. The growth and nitrogen uptake of S. nanum was higher when immobilized than when cultured in suspension. S. nanum preferred ammonia rather than nitrate as nitrogen species. Further effects of S. nanum on the RAS water quality (total ammonia nitrogen (TAN), nitrite, nitrate, and phosphate) were also investigated. No difference of TAN between the RAS with algae (RAS+A) and the RAS without algae (RAS-A) was observed. However, nitrite, nitrate and phosphate were significantly lower in the RAS+A than in the RAS-A. When the RAS systems were perturbed by an acute pH drop (from pH 7 to 4 over three hours), no significant difference was observed between the RAS+A and the RAS-A on the resistance towards the stressor. This was shown by an increase in the TAN and the nitrite concentration in both treatments after the perturbation. However, the algae helped the RAS+A to regain a low nitrite level faster than the RAS-A. The diversity of bacterial community between the RAS+A and the RAS-A was not different, while the composition of bacterial community was significantly different between the RAS+A and the RAS-A, thus influencing the functioning of the RAS.</p
Upgrading low-quality feeds for tilapia by enzyme and probiotic supplementation
No full textWith the expected further growth of aquaculture and the increasing demand for aquafeeds, the trend for reducing levels of fishmeal and fish-oil in these feeds will continue. The use of lower quality ingredients for many fish species, including tilapia, will increase in the future, leading to increased dietary levels of anti-nutritional factors, including non-starch polysaccharides (NSP) and phytate. Both NSP and phytate are considered indigestible, as the enzymes needed to breakdown their bonds are scarce or non-existent in fish. Supplementing feeds with dietary enzymes and probiotics can reduce the antinutritional effects of phytate and NSP. However, compared to other monogastric animals, studies on fish using phytase and NSP-degrading enzymes are scarce. Likewise, multiple studies have been performed, both on broilers and pigs on the improvement of nutrient bioavailability with the use of probiotics. However, for fish similar studies are few in number; little is currently known as to how probiotics can improve nutrient bioavailability of plant-based aquafeeds. In addition, it is expected that in fish there may be synergy between different enzymes, and between enzymes and probiotics, but this has not yet been assessed. Therefore the aim of this thesis is to assess the potential of dietary enzyme and probiotic supplementation in improving the nutritional value of low quality feed ingredients, using Nile tilapia as a model species.The main conclusions of the thesis are:NSP is not inert to digestion.Phytase improved the availability of phosphorus, calcium and crude ash fractions in the diet.Xylanase has the potential to improve nutrient digestibility.β-glucanase did not improve nutrient digestibility.Probiotic supplementation improved fat digestibility.Probiotics improved growth and reduced the energy requirements for maintenance.In Nile tilapia, the available phosphorus requirement is greater than 7 g/kg feed (dry matter).The combination of enzymes and probiotics enhanced microbial interactions in the distal gut.Enzymes, when supplemented to the diet, are mainly active in the stomach.The effect of enzyme supplementation is dependent on diet quality.Synergy between phytase and xylanase can occur.Overall it can be concluded that, in Nile tilapia, the nutritional value of low quality diets was improved with exogenous enzyme and probiotic supplementation, resulting in enhanced growth performance. This implies that an increasing proportion of low quality plant-based co- and by-products could be incorporated into aquafeeds, thus contributing to the development of circular food systems. 
Nutritious ponds : valorising waste using natural production
No full textThese days understanding and predicting impacts of anthropogenic climate change caused by greenhouse gas emissions (rising temperatures and acidification of oceans), and exploitation of natural resources (overexploitation and waste production) on ecosystem dynamics is a major issue. With the world population increasing, there is demand to produce more food, which impinges with the wish to reduce waste output and lower the use of limited resources. Aquaculture has the potential to increase production by intensification, but to do so, the sector is facing major sustainability challenges. Two major issues hindering sustainable intensification are waste residues in pond culture water, and the use of capture fisheries derived fishmeal and fish oil in aquaculture diets as source of highly unsaturated omega-3 fatty acids (HUFA). This thesis advocates for developing the “nutritious pond concept” where the focus should shift from feeding the culture-animal, to feeding the whole system. In this way, a balanced food web develops, supporting production and good water quality. In this way, aquaculture production can be made more ecological while maintaining high production levels. In chapter 2, the contribution of HUFA from dietary fish oil and fishmeal, and the natural food web on shrimp production was determined. Fatty acid mass balances were computed to distinguish between formulated diet-based and primary production-based HUFA contribution. Absence of both fish oil and fishmeal in the formulated diet did not reduce shrimp production. However, shrimp fed diets lacking fish oil and fishmeal contained only half of the HUFA compared to control shrimp. In both dietary treatment groups, large dietary quantitative losses of the precursors ALA and LA were observed that were being used as energy source instead of HUFA synthesis. Whereas losses were also observed for EPA and DHA in the control group, there was a remarkable gain for these components in shrimp fed diets free of fish oil and fishmeal. Shrimp acquired at least 32 % of their EPA and 6 % of their DHA content from the algal-based food web. These findings strongly suggested that the pond’s natural food web produced HUFA that supports shrimp production. In chapter 3, the in situ produced HUFA was quantified per food web compartment. Seston was found to contain the highest HUFA content in the mesocosm, while biofloc dominated in terms of biomass. The total HUFA production in the mesocosms was a more than 600 % increase compared to the minimal HUFA-input in the tanks receiving HUFA-deficient diets, pinpointing de novo in situ production. Most of the formulated feed input resulted in organic matter biomass accumulation other than shrimp, as shrimp only retained 12 % of the organic matter input. This showed that the system as a whole is quite efficient in converting nutrient input into different food web compartment, but shrimp production alone is quite inefficient. With shrimp harvesting, only 25 – 27 % of the total mesocosm HUFA content is removed from the system. The majority of the nutrients, including de novo produced HUFA, remained in the food web. This exposed a major challenge on finding ways to reclaim those nutrients from the system in a more efficient way. This challenge was reinforced by the outcomes in chapter 4, focussing on nitrogen (protein), showing large amounts of total mesocosm nitrogen content could be found in food web compartments other than shrimp. Lowering the feed:fertilizer ratio of the mesocosm input by replacing 50 % of the formulated feed with carbon and nitrogen fertilizers (thus reducing protein input by half), lead to a 48 % increase of food web protein contribution to shrimp protein content. Total natural food protein contribution was estimated at 74 %. Feed conversion ratio was below 1.0 in all treatments and decreased with decreasing feed:fertilizer ratio down to 0.48. The nitrogen-to-protein conversion factor of flocculated matter in the water column was determined and found to be 7.31, higher than expected. Estimating food web protein contents using this factor, showed that a similar equivalent of protein as in shrimp, was accumulated in biofloc and periphyton combined, that remained unused in the system after shrimp harvest. Finding ways to use this protein (nitrogen) in the food web, would allow for reducing protein content in formulated diets. Lowering phosphorous input to the system with 50 %, had no effect on HUFA content of the food web and increased shrimp phosphorous retention from 16 to 34 %. Replacing up to 50 % of the feed input with carbohydrate and inorganic nitrogen that was directly accessible to the pond’s microbiota, did not result in differences in nutrient distribution and C:N:P ratios in food web compartments including shrimp in chapter 5. Natural food contribution to shrimp production increased significantly with reducing feeding level and increasing carbohydrate and inorganic nitrogen supplementation, but only if the system was within maximum carrying capacity. Computing mass balances of phosphorous revealed that following a > 30 % reduced system phosphorous input, flows of phosphorous in the food web changed. As a result, phosphorous from detritus flowed into periphyton in such rate that depletion would have occurred within one shrimp production cycle. This meant that when developing a nutritious pond diet where part of the feed is replaced with carbon and nitrogen fertilizer, phosphorous should be added too to prevent depletion, but reducing total phosphorous input up to 20 % is possible. Finally, chapter 6 synthesized the outcomes from this thesis by placing results into a broader context. The outcomes and recommendations following this thesis may contribute to the way we look at aquaculture in relation to sustainability, limited resources, climate change, nutrient flows, nutritional value of aquaculture products, and aquaculture ecology. With a still increasing world population there is need to change our current food production systems towards circular production systems. Climate change is going to affect aquaculture production and can be an extra challenge in order to further develop the nutritious pond concept, especially concerning de novo HUFA production in de pond. Nevertheless, the nutritious pond concept forms a crucial step towards a more sustainable aquaculture, independent of capture fisheries
Bile acids in rainbow trout : Keeping a balance
No full textIn mammals, effects of dietary factors on the bile acid metabolism and the relationship with fat digestibility have been extensively studied. Such information is largely lacking in fish, and this despite several indications that dietary changes associated with the transition from fishmeal-based to plant-based diets can affect the bile acid metabolism and fat digestion in fish. Fat is an important energy source for fish, especially for carnivorous species. Given the importance of bile acids for proper fat digestion, understanding how dietary factors affect the bile acid metabolism is of value for future aquaculture production. This thesis aimed to increase insights on how dietary factors can affect the bile acid metabolism of rainbow trout and on how disruptions of the bile acid metabolism reflect on fat digestibility. From the results of the different experiments carried out in this thesis, the following conclusions were made:• Several nutritional factors can alter faecal bile acid content in rainbow trout (e.g., protein source, non-starch polysaccharide level, bile acid supplementation and feeding level).Contrasting findings, both within this thesis and between literature, show that many more factors, which are currently not known, affect faecal bile acid content.• Regardless of faecal bile acid content, factors that lower dry matter ADC and/or increase feed intake (i.e., factors that increase faecal waste production) can enhance faecal bile acid loss in rainbow trout.• Hampered fat digestion in rainbow trout with enhanced faecal bile acid loss seems related to a lack of emulsification capacity in the small intestine as shown by the positive effect of bile acid supplementation on fat ADC, while absent for ADC of protein and carbohydrates.• Diets that supply lower levels of cholesterol, minimal taurine and that meet amino acid requirements (plant-based diet) do not hamper fat digestion and are most likely not limiting for the bile acid metabolism of rainbow trout. Plant-based diets were not limiting for fat digestion, which most likely was related to these diets resulting in a lower feed intake compared to fishmeal-based diets.• The total body bile acid pool size of rainbow trout (μmol fish-1) increases with body weight. This increase seems to be linear, however, this thesis shows that the rate of increase can be altered by diet composition (e.g., NSP level and type of non-protein energy source).• Bile acid synthesis in rainbow trout can be quantitatively altered depending on diet composition (e.g., bile acid supplementation and type of non-protein energy source).• The efficiency of enterohepatic circulation of rainbow trout’s body own taurocholic acid does not differ from that of body foreign glycocholic acid.• Although relative absorption of bile acids in the intestine was highest in the distal intestine, more than half of the bile acids is absorbed in the proximal intestine of rainbow trout.• Rainbow trout has a better intestinal conservation of cholic acid compared to chenodeoxycholic acid.This thesis was the first to quantify disruptions of the bile acid metabolism in fish. Several contradictory results in the observed effects of the investigated dietary factors on the bile acid metabolism and fat digestion show that there are many more unknow factors which were not considered and thus need to be clarified by future research. Factors that enhance faecal bile acid loss seem to hamper fat digestion in rainbow trout. Further research is now needed to clarify the reason for the inverse relationship between faecal bile acid loss and fat digestion, and validate the proposed concept of total bile acid pool size depletion by enhanced faecal bile acid loss due to the limited capacity for bile acid synthesi
The contribution of mangrove leaf litter to juvenile shrimp (Penaeus monodon) production in mangrove-shrimp aquaculture systems
No full textIntensification of shrimp farming has been identified as one of the main causes for mangrove destruction in the coastal region of many countries. The idea to develop mangrove-shrimp co-management was developed during the last decades of the 20th century as an effort to help restore the mangrove ecosystem and make shrimp culture sustainable. The present research is part of a broader effort to introduce silvo-aquaculture, combining mangrove and shrimp, to Bangladesh. Mangrove- shrimp co-management has very high potential from an ecological and economical point of view. Mangrove leaf litter are shown to enhance shrimp production by enhancing natural food production. In addition, the nutrient use efficiency of artificial feed is found to be enhanced by providing leaf litter as extra nutrient source, a form of synergism between natural and artificial feed. Therefore the main aim of this thesis is to assess the impact of leaf litter from different mangrove species on pond performance, water quality and natural food availability in mangrove shrimp nursery tanks and ponds. First of all, the nutrient and anti-nutrient content in leaf litter of selected mangrove species and their effect on shrimp performance were determined. The observed effects on post-larval shrimp differed between mangrove species, showing a clear ranking of mangrove species in terms of their ability to enhance shrimp growth. Leaf litter from different mangrove species, not only led to different concentrations of plankton in the PL nursery tank system, but also correlated with shrimp growth performance. Secondly, the effects of interactions between leaf litter from the four chosen mangrove species and pelleted feed on shrimp growth and survival in shrimp PL nursery tanks were explored. Leaf litter and feed combined, resulted in a 21 to 33% higher weight gain of shrimp PL than based on the additive contributions of only leaf litter or only feed, indicating a synergistic effect of the two food sources on shrimp growth. Among the different mangrove species tested, S. apetala (Sa; 23.1%) contributed the most to total weight gain followed by A. officinalis (Ao; 21.6%), S. caseolaris (Sc; 21.6%) and H. fomes (Hf; 10%). The lower feed conversion ratio (FCR) (0.18–0.27) in the treatments combining leaf litter and supplemental feed as compared to the feed-only treatment (0.41) indicated that leaf litter (directly or indirectly by stimulating natural food production) contributed to the nutrition of the shrimp. The observed synergistic effect between supplemental feed and leaf litter is an opportunity for farmers to reduce shrimp production costs and simultaneously raise benefits. Thirdly, effect of different combinations of leaf litter from different mangrove species on shrimp larval performance in tanks and small (mesocosm) ponds were also explored. Three 3-mangrove-species and one 4-mangrove-species combinations of mangrove leaf litter were tested. Under controlled conditions in tanks, mixed leaf litter and feed resulted in 22 to 32% higher weight gain of PL than based on the additive contributions of only leaf litter or only feed, indicating a similar synergistic effect of the two food sources on shrimp growth . Although the nutrient input level and PL stocking density in ponds were less than half the input or density in tanks, the shrimp grew 3.5 times larger in the mesocosm ponds. The different combinations of mangrove leaf litter employed influenced water quality and stimulated the production of phytoplankton and zooplankton food, which allowed greater shrimp weight gain. Then, effect of leaf litter on shrimp growth, color and product appeal to farmers, exporters and local consumers was identified. The body color of shrimp not exposed to leaf litter was lighter than of shrimp grown in tanks receiving leaf litter. The majority of Sa-reared shrimp at harvest were significantly darker (P < 0.05) in body color than larvae reared with leaf litter from other mangrove species. The shrimp body color of shrimp not exposed to any leaf litter at all was lighter than of shrimp reared in presence of all types of leaf litter tested. Within each category of shrimp value-chain actors interviewed, more than 50% of respondents preferred dark colored shrimp, and none preferred pale-colored shrimp. 100% from among exporters and local consumers, respectively, 100% and 60% linked dark body color to higher price, while the opposite was the case among non-mangrove farmers. Aside from production volume, mangrove leaf litter was found to strongly enhance the color properties and hence perceived quality of black tiger shrimp to the consumer. Inclusion of mangroves in and along shrimp culture ponds is recommended as a valuable way of improving both the commercial profitability and sustainability of shrimp aquaculture in Bangladesh and elsewhere.Finally, the effectiveness of mangrove leaf litter application in combination with pelleted supplemental feed in PL nursery systems is reviewed against existing concepts and the functioning of mangrove-shrimp rearing systems.The main identifications are:Application of mangrove leaf litter contributes to individual growth and total production in shrimp nursery systems.When applied at 1 kg m-3 and 0.56 kg m-3 culture volume in tanks and mesocosm ponds, respectively, the anti-nutrient content in leaf litter does not negatively impact shrimp performance.Crude fiber content strongly affects the decomposition rate of mangrove leaf litter.Leaf litter decomposition at the described leaf litter loading rates releases nutrients that stimulate plankton production, which in turn enhance the total system performance of shrimp nursery systems.For the input range and culture duration, applied in this Thesis project, joint application of supplemental pelleted feed and mangrove leaf litter created synergy for a more than additive positive effect on shrimp growth.The traditional shrimp farmers in Bangladesh need to be introduced to and trained in mangrove-shrimp co-management rearing techniques to ensure they benefit from mangrove-shrimp aquaculture.Overall, our results show that inclusion of mangroves in shrimp pond culture has great as yet largely untapped potential to enhance pond productivity and make shrimp farming more environmentally sustainable. A paradigm shift is needed with respect to mangroves vis-a-vis shrimp pond aquaculture. Whereas these areas today are largely denuded of mangrove trees, these should be seen as valuable resource for the shrimp farmer of which the leaves can serves as a healthy and inexpensive source of shrimp food. Proper management of mangrove trees in and around shrimp ponds is an opportunity with which to make shrimp farming more resilient, with important benefits for the coastal communities and the coastal ecosystem
Two aspects of aquaculture systems: resource use and the accumulation of organic wastes.
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