Optimising Integrated Multitrophic Aquaculture (IMTA) on a South African abalone farm
- Authors: Falade, Abiodun Emmanuel
- Date: 2024-10-11
- Subjects: Aquaculture , Integrated multi-trophic aquaculture , Seaweed , Abalone culture South Africa , Abalones , Ingestion , Nutrient cycles
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/466712 , vital:76772 , DOI https://doi.org/10.21504/10962/466712
- Description: The efficiency of fed nutrient utilisation in integrated multitrophic aquaculture (IMTA) system was evaluated on a South African abalone farm. On many commercial abalone farms in South Africa, Haliotis midae are fed a combination of pelleted feed and live macroalgae cultured downstream in abalone effluent. This production technique reduces the discharge of dissolved nutrients into the environment and improves farm productivity as unquantified proportion of the waste metabolites is captured as macroalgal biomass. However, the solid waste from abalone culture tanks remains unutilised and discharged to the coastal environments. Thus, there is scope to improve the dissolved nutrients removal efficiency of the macroalgae and to reduce the discharge of particulate nutrients using detritus waste extractive organisms. The present study aimed at the production and environmental performance of a shore-based abalone/macroalgae IMTA improving farm in South Africa by improving the nutrient utilisation efficiency of farmed abalone and seaweed and testing the waste solids removal potential of a sea cucumber species. Monoculture systems, where abalone and seaweed were cultured separately, both in fresh seawater (salinity: 35 g/L), were compared with an integrated culture system where the seaweed (Ulva lacinulata) was cultured downstream in the wastewater flowing from abalone tanks that were up-channel. Based on the findings from quantifying the performance of these production systems, methods to improve the nutrient utilisation and production efficiencies of the production systems were explored. These assessed methods included (1) the removal of abalone biodeposits by detritus extractive sea cucumber production, (2) evaluating the potential of farmed macroalgae as supplement in formulated diet, and (3) replacing mineral fertilisers with eco-friendly live microbial fertilisers for seaweed farming. Furthermore, the overall environmental performance of the two farm systems was quantified using a life cycle analysis methodology. Monitoring of the nutrient flows through the monoculture and IMTA systems revealed that the highest inputs of nutrients (nitrogen and phosphorus) into the abalone and seaweed culture tanks of the two production systems were abalone feed pellet (70-81%) and mineral fertilisers respectively (63-93%). About 48-51% of the nitrogen supplied from the feed was utilised by abalone in the IMTA and monoculture systems, while the remaining portion was lost as organic waste nitrogen on the production tank floor (20-30%) and as dissolved nitrogen in post-abalone tank effluent (30-36%). In the seaweed tanks receiving abalone effluent (IMTA), 69% of the dissolved nitrogen input was absorbed by cultured Ulva while 25% of the nitrogen was lost to the post-seaweed effluent which returned to the environment. However, in the monoculture system, 52% of the nitrogen from supplemented inorganic fertiliser was absorbed by cultured Ulva while ca. 46% of the nutrient was lost to coastal waters through the post-seaweed effluent. Moreover, while the feed accounted for ca. 74-78% input of the phosphorus in abalone of the two production systems, not more than 19% and 13% of this phosphorus was utilised by H. midae in the IMTA and monoculture systems respectively, while the largest portions were lost as organic waste in the sediment (34-45%) and dissolved waste phosphorus in the effluent (33-54%). In the seaweed tanks, a small portion (11-15%) of supplied phosphorus was removed by farmed Ulva while 77-89% was lost in the post-seaweed effluent discharged to coastal environment. The substitution of 50% mineral fertilisers with live microbial fertilisers during seaweed production significantly reduced the discharge of dissolved nitrogen and phosphorus from macroalgae raceways to coastal environment by 55 and 45% respectively, without impacting their growth, yield and nutrient compositions. A life cycle analysis of the measured energy and nutrients utilisation efficiency of these production systems was compiled, and the impacts of the inputs and outputs from each production system on the environment was assessed. The electrical energy input to abalone and seaweed tanks constituted the highest contribution to all assessed environmental impact categories for the two production systems, followed by the contributions from the nutrients supplied to farmed abalone (formulated diet) and seaweed (mineral fertilisers). The impact of these inputs on the environment was most evident on marine aquatic ecotoxicity being 2.11E+03 kg 1.4-DB eq and 4.43E+03 kg 1.4-DB eq for IMTA and monoculture systems respectively. The measured impact of seaweed aquaculture on the environment was reduced by 50-52% when Ulva was cultured in abalone effluent (IMTA) compared to culture in fresh seawater (monoculture). However, the input of chemical fertilisers in the two systems of cultivation resulted in similar eutrophication potentials (8.09 - 8.41E-02 kg PO4--- eq). To reduce the solid waste discharge from abalone tanks, and create an additional high-value crop, an endemic sea cucumber species (Neostichopus grammatus) was introduced on the floor of the abalone culture tanks in a pilot abalone/detritivore/macroalgae IMTA system. The sea cucumber utilised the biodeposits in abalone tanks as food which reduced organic solid discharge to the environment by 11%. However, the sea cucumbers displayed poor nutrient utilisation, a negative growth rate (- 0.59% day-1) and 49% weight loss by the end of the trial that was probably due to sub-optimal habitat conditions (lack of a sand substrate). The potential of including farmed Ulva (IMTA and monoculture) meal in pelleted feed for H. midae was evaluated as a means of improving farming efficiency and reducing the levels of fishmeal and soya in the pellet. In an initial trial, Ulva was included at 12% dry weight in commercial diet and fed to farmed H. midae for 244 d. The 12% inclusion of IMTA and monoculture Ulva resulted in poor feed conversion and nutrient utilisation by H. midae. In a follow-up trial which tested graded inclusion levels of Ulva meal (0.75, 1.50, 3.00, 6.00 and 12.00%), the growth rate and feed utilisation of H. midae was enhanced at a 0.75-6.00% inclusion level of the seaweed in the diet, while at a 6.00-12.00% inclusion level growth rates and feed conversion efficiencies decreased. Therefore, it is recommended that for sub-adult South African abalone, up to 6.00% IMTA Ulva meal can be included in the diet formulation without impacting their growth performance and nutrient utilisation efficiency negatively. This present study contributes to the understanding of the nutrient utilisation dynamics on integrated abalone farms in South Africa. The evidence from the different trials suggests the IMTA techniques tested could be adopted to improve the production performance and reduce the impact of abalone farming on the environment. , Thesis (PhD) -- Faculty of Science, Ichthyology and Fisheries Science, 2024
- Full Text:
- Date Issued: 2024-10-11
- Authors: Falade, Abiodun Emmanuel
- Date: 2024-10-11
- Subjects: Aquaculture , Integrated multi-trophic aquaculture , Seaweed , Abalone culture South Africa , Abalones , Ingestion , Nutrient cycles
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/466712 , vital:76772 , DOI https://doi.org/10.21504/10962/466712
- Description: The efficiency of fed nutrient utilisation in integrated multitrophic aquaculture (IMTA) system was evaluated on a South African abalone farm. On many commercial abalone farms in South Africa, Haliotis midae are fed a combination of pelleted feed and live macroalgae cultured downstream in abalone effluent. This production technique reduces the discharge of dissolved nutrients into the environment and improves farm productivity as unquantified proportion of the waste metabolites is captured as macroalgal biomass. However, the solid waste from abalone culture tanks remains unutilised and discharged to the coastal environments. Thus, there is scope to improve the dissolved nutrients removal efficiency of the macroalgae and to reduce the discharge of particulate nutrients using detritus waste extractive organisms. The present study aimed at the production and environmental performance of a shore-based abalone/macroalgae IMTA improving farm in South Africa by improving the nutrient utilisation efficiency of farmed abalone and seaweed and testing the waste solids removal potential of a sea cucumber species. Monoculture systems, where abalone and seaweed were cultured separately, both in fresh seawater (salinity: 35 g/L), were compared with an integrated culture system where the seaweed (Ulva lacinulata) was cultured downstream in the wastewater flowing from abalone tanks that were up-channel. Based on the findings from quantifying the performance of these production systems, methods to improve the nutrient utilisation and production efficiencies of the production systems were explored. These assessed methods included (1) the removal of abalone biodeposits by detritus extractive sea cucumber production, (2) evaluating the potential of farmed macroalgae as supplement in formulated diet, and (3) replacing mineral fertilisers with eco-friendly live microbial fertilisers for seaweed farming. Furthermore, the overall environmental performance of the two farm systems was quantified using a life cycle analysis methodology. Monitoring of the nutrient flows through the monoculture and IMTA systems revealed that the highest inputs of nutrients (nitrogen and phosphorus) into the abalone and seaweed culture tanks of the two production systems were abalone feed pellet (70-81%) and mineral fertilisers respectively (63-93%). About 48-51% of the nitrogen supplied from the feed was utilised by abalone in the IMTA and monoculture systems, while the remaining portion was lost as organic waste nitrogen on the production tank floor (20-30%) and as dissolved nitrogen in post-abalone tank effluent (30-36%). In the seaweed tanks receiving abalone effluent (IMTA), 69% of the dissolved nitrogen input was absorbed by cultured Ulva while 25% of the nitrogen was lost to the post-seaweed effluent which returned to the environment. However, in the monoculture system, 52% of the nitrogen from supplemented inorganic fertiliser was absorbed by cultured Ulva while ca. 46% of the nutrient was lost to coastal waters through the post-seaweed effluent. Moreover, while the feed accounted for ca. 74-78% input of the phosphorus in abalone of the two production systems, not more than 19% and 13% of this phosphorus was utilised by H. midae in the IMTA and monoculture systems respectively, while the largest portions were lost as organic waste in the sediment (34-45%) and dissolved waste phosphorus in the effluent (33-54%). In the seaweed tanks, a small portion (11-15%) of supplied phosphorus was removed by farmed Ulva while 77-89% was lost in the post-seaweed effluent discharged to coastal environment. The substitution of 50% mineral fertilisers with live microbial fertilisers during seaweed production significantly reduced the discharge of dissolved nitrogen and phosphorus from macroalgae raceways to coastal environment by 55 and 45% respectively, without impacting their growth, yield and nutrient compositions. A life cycle analysis of the measured energy and nutrients utilisation efficiency of these production systems was compiled, and the impacts of the inputs and outputs from each production system on the environment was assessed. The electrical energy input to abalone and seaweed tanks constituted the highest contribution to all assessed environmental impact categories for the two production systems, followed by the contributions from the nutrients supplied to farmed abalone (formulated diet) and seaweed (mineral fertilisers). The impact of these inputs on the environment was most evident on marine aquatic ecotoxicity being 2.11E+03 kg 1.4-DB eq and 4.43E+03 kg 1.4-DB eq for IMTA and monoculture systems respectively. The measured impact of seaweed aquaculture on the environment was reduced by 50-52% when Ulva was cultured in abalone effluent (IMTA) compared to culture in fresh seawater (monoculture). However, the input of chemical fertilisers in the two systems of cultivation resulted in similar eutrophication potentials (8.09 - 8.41E-02 kg PO4--- eq). To reduce the solid waste discharge from abalone tanks, and create an additional high-value crop, an endemic sea cucumber species (Neostichopus grammatus) was introduced on the floor of the abalone culture tanks in a pilot abalone/detritivore/macroalgae IMTA system. The sea cucumber utilised the biodeposits in abalone tanks as food which reduced organic solid discharge to the environment by 11%. However, the sea cucumbers displayed poor nutrient utilisation, a negative growth rate (- 0.59% day-1) and 49% weight loss by the end of the trial that was probably due to sub-optimal habitat conditions (lack of a sand substrate). The potential of including farmed Ulva (IMTA and monoculture) meal in pelleted feed for H. midae was evaluated as a means of improving farming efficiency and reducing the levels of fishmeal and soya in the pellet. In an initial trial, Ulva was included at 12% dry weight in commercial diet and fed to farmed H. midae for 244 d. The 12% inclusion of IMTA and monoculture Ulva resulted in poor feed conversion and nutrient utilisation by H. midae. In a follow-up trial which tested graded inclusion levels of Ulva meal (0.75, 1.50, 3.00, 6.00 and 12.00%), the growth rate and feed utilisation of H. midae was enhanced at a 0.75-6.00% inclusion level of the seaweed in the diet, while at a 6.00-12.00% inclusion level growth rates and feed conversion efficiencies decreased. Therefore, it is recommended that for sub-adult South African abalone, up to 6.00% IMTA Ulva meal can be included in the diet formulation without impacting their growth performance and nutrient utilisation efficiency negatively. This present study contributes to the understanding of the nutrient utilisation dynamics on integrated abalone farms in South Africa. The evidence from the different trials suggests the IMTA techniques tested could be adopted to improve the production performance and reduce the impact of abalone farming on the environment. , Thesis (PhD) -- Faculty of Science, Ichthyology and Fisheries Science, 2024
- Full Text:
- Date Issued: 2024-10-11
Mitigating salt accumulation in recycled brewery effluent through the integration of water treatment, agriculture and aquaculture
- Authors: Mabasa, Nyiko Charity
- Date: 2021-10-29
- Subjects: Brewery waste South Africa Eastern Cape , Recycling (Waste, etc.) South Africa Eastern Cape , Water reuse South Africa Eastern Cape , Irrigation South Africa Eastern Cape , Sewage Purification Anaerobic treatment , Constructed wetlands , Aquaculture
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/191126 , vital:45063 , 10.21504/10962/191126
- Description: Water scarcity in South Africa, and globally, presents challenges for industries. It is imperative to develop responsible water use, such as recycling and reusing wastewater from food processing industries such as breweries. The Ibhayi Brewery (SAB Ltd) employs a combination of sustainable treatment processes that include anaerobic digestion (AD), primary facultative ponds (PFP), high rate algal ponds (HRAP) and constructed wetlands (CW) to treat brewery effluent on an experimental scale. The constituent concentrations of these experimentally treated effluents are within the ranges prescribed by local regulations to allow for potential downstream use in agriculture and aquaculture. However, the sodium content in this treated effluent, which originates from upstream cleaning agents and pH control at the onsite effluent treatment facility, is a constraint to the downstream use of brewery effluent. This study addresses the salt problem, by investigating the potential of either reducing/eliminating salt addition at source, or developing alternative techniques for downstream agriculture to mitigate the effects of salt accumulation caused by irrigation with brewery effluent. Four salt-tolerant test crops; Swiss chard (Beta vulgaris), saltbush (Atriplex nummularia), Salicornia meyeriana and sorghum (Sorghum bicolor), grew efficiently in brewery effluent irrigated soils but did not stop sodium accumulation in the growth medium. Swiss chard had the best growth with a wet biomass accumulation of 8,173 g m-2, due to the plant’s ability to tolerate saline conditions and continuous cropping. Crop rotation, to limit effects of nutrient depletion in soil, had no significant effect on plant growth suggesting soils were adequately able to provide micro-nutrients in the short-term. Prolonged irrigation with brewery effluent can lead to sodium accumulation in the soil, which was successfully controlled through the addition of soil amendments (gypsum and Trichoderma cultures). These reduced soil sodium from a potentially limiting level of 1,398 mg L-1 to the acceptable levels of 240 mg L-1 and 353 mg L-1 respectively, mainly through leaching. However only Trichoderma improved Swiss chard production to 11,238 g m-2. While crop rotation in this work did not contribute to mitigating the problem of salt accumulation, soil amended with Trichoderma appears to be a potential solution when brewery effluent is reused in agriculture. In an alternative to soil cultivation, CWs were trialled with no significant differences in the sodium concentration of brewery effluent treated along a 15 m lateral flow CW, which could be attributed to evapotranspiration. This was notably accompanied by a desirable 95.21% decrease in ammonia from inlet to outlet resulting in significant improvement in water quality for reuse in aquaculture where ammonia levels are important limiting constraints. While CWs remain a suitable brewery effluent treatment solution, this technology requires additional modelling and optimisation in order to mitigate the problem of salt accumulation in the reuse of treated brewery effluent in agriculture and aquaculture. This research demonstrates the baseline information for such modelling and optimisation. African catfish (Clarias gariepinus) grew in CW treated brewery effluent; however, this growth was moderate at 0.92% bw day-1, whereas Mozambique tilapia (Oreochromis mossambicus) were shown to be unsuited to growth in this system and lost weight with an average specific growth rate (SGR) of -0.98% bw day-1; and both fish species presenting with health related concerns. Hardy fish species such as African catfish can be cultured in brewery effluent, but with risk involved. This was a preliminary study to develop parameters for future dimensional analysis modelling to allow optimisation of the CW, based on nutrient removal rates obtained which will allow for improved downstream aquaculture by reducing or eliminating risks presented in this study. This work has also contributed to a foundation for the development of guidelines that use a risk-based approach for water use in aquaculture. Alternatives to the current in place cleaning agents were considered to mitigate the effects of salt accumulation. Sodium is introduced into the effluent via the use of sodium hydroxide and sodium chlorite for cleaning and disinfection in the brewery, as well as through effluent pH adjustment in the AD plant. The widespread use of outdated legacy cleaning systems and pH adjustment regimes is entrenched in the brewery standard operating procedures (SOP). A cost-benefit analysis (CBA) demonstrated that a change of cleaning and disinfecting regimes to hydrogen peroxide in the brewery, and magnesium hydroxide pH adjustment in the effluent treatment plant addresses the sodium issue upstream in the brewery practically eliminating sodium from the effluent. In addition, a life cycle analysis (LCA) was carried out to assess the environmental impacts associated with the alternative cleaning and pH adjustment scenarios. The LCA showed that electricity consumption during use phase of the chemicals for respective purposes, as well as their production activities were major contributors to the significant environmental impact categories that were assessed. The cleaning scenario employing the use of hydrogen peroxide for both cleaning and disinfection was found to be the most environmentally sustainable. This was attributed to the reduced number of chemicals used compared to the other cleaning scenarios. Dolomitic lime was the pH adjustment alternative with the lowest average environmental impact; but, however, had a higher impact on freshwater eutrophication which is of major concern if the effluent will be reused for irrigation. Magnesium hydroxide was therefore considered to be the better option as a sodium hydroxide alternative for pH adjustment. This mitigates salt accumulation, making treated brewery effluent suitable for reuse in high value downstream agriculture and aquaculture, while employing more environmentally sustainable technologies. Notably, this converts brewery effluent from a financial liability to Ibhayi Brewery, into a product containing water and nutrients that generate income, improve food security, and can create employment in downstream agriculture and aquaculture in a sustainable manner. , Thesis (PhD) -- Faculty of Science, Ichthyology and Fisheries Science, 2021
- Full Text:
- Date Issued: 2021-10-29
- Authors: Mabasa, Nyiko Charity
- Date: 2021-10-29
- Subjects: Brewery waste South Africa Eastern Cape , Recycling (Waste, etc.) South Africa Eastern Cape , Water reuse South Africa Eastern Cape , Irrigation South Africa Eastern Cape , Sewage Purification Anaerobic treatment , Constructed wetlands , Aquaculture
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/191126 , vital:45063 , 10.21504/10962/191126
- Description: Water scarcity in South Africa, and globally, presents challenges for industries. It is imperative to develop responsible water use, such as recycling and reusing wastewater from food processing industries such as breweries. The Ibhayi Brewery (SAB Ltd) employs a combination of sustainable treatment processes that include anaerobic digestion (AD), primary facultative ponds (PFP), high rate algal ponds (HRAP) and constructed wetlands (CW) to treat brewery effluent on an experimental scale. The constituent concentrations of these experimentally treated effluents are within the ranges prescribed by local regulations to allow for potential downstream use in agriculture and aquaculture. However, the sodium content in this treated effluent, which originates from upstream cleaning agents and pH control at the onsite effluent treatment facility, is a constraint to the downstream use of brewery effluent. This study addresses the salt problem, by investigating the potential of either reducing/eliminating salt addition at source, or developing alternative techniques for downstream agriculture to mitigate the effects of salt accumulation caused by irrigation with brewery effluent. Four salt-tolerant test crops; Swiss chard (Beta vulgaris), saltbush (Atriplex nummularia), Salicornia meyeriana and sorghum (Sorghum bicolor), grew efficiently in brewery effluent irrigated soils but did not stop sodium accumulation in the growth medium. Swiss chard had the best growth with a wet biomass accumulation of 8,173 g m-2, due to the plant’s ability to tolerate saline conditions and continuous cropping. Crop rotation, to limit effects of nutrient depletion in soil, had no significant effect on plant growth suggesting soils were adequately able to provide micro-nutrients in the short-term. Prolonged irrigation with brewery effluent can lead to sodium accumulation in the soil, which was successfully controlled through the addition of soil amendments (gypsum and Trichoderma cultures). These reduced soil sodium from a potentially limiting level of 1,398 mg L-1 to the acceptable levels of 240 mg L-1 and 353 mg L-1 respectively, mainly through leaching. However only Trichoderma improved Swiss chard production to 11,238 g m-2. While crop rotation in this work did not contribute to mitigating the problem of salt accumulation, soil amended with Trichoderma appears to be a potential solution when brewery effluent is reused in agriculture. In an alternative to soil cultivation, CWs were trialled with no significant differences in the sodium concentration of brewery effluent treated along a 15 m lateral flow CW, which could be attributed to evapotranspiration. This was notably accompanied by a desirable 95.21% decrease in ammonia from inlet to outlet resulting in significant improvement in water quality for reuse in aquaculture where ammonia levels are important limiting constraints. While CWs remain a suitable brewery effluent treatment solution, this technology requires additional modelling and optimisation in order to mitigate the problem of salt accumulation in the reuse of treated brewery effluent in agriculture and aquaculture. This research demonstrates the baseline information for such modelling and optimisation. African catfish (Clarias gariepinus) grew in CW treated brewery effluent; however, this growth was moderate at 0.92% bw day-1, whereas Mozambique tilapia (Oreochromis mossambicus) were shown to be unsuited to growth in this system and lost weight with an average specific growth rate (SGR) of -0.98% bw day-1; and both fish species presenting with health related concerns. Hardy fish species such as African catfish can be cultured in brewery effluent, but with risk involved. This was a preliminary study to develop parameters for future dimensional analysis modelling to allow optimisation of the CW, based on nutrient removal rates obtained which will allow for improved downstream aquaculture by reducing or eliminating risks presented in this study. This work has also contributed to a foundation for the development of guidelines that use a risk-based approach for water use in aquaculture. Alternatives to the current in place cleaning agents were considered to mitigate the effects of salt accumulation. Sodium is introduced into the effluent via the use of sodium hydroxide and sodium chlorite for cleaning and disinfection in the brewery, as well as through effluent pH adjustment in the AD plant. The widespread use of outdated legacy cleaning systems and pH adjustment regimes is entrenched in the brewery standard operating procedures (SOP). A cost-benefit analysis (CBA) demonstrated that a change of cleaning and disinfecting regimes to hydrogen peroxide in the brewery, and magnesium hydroxide pH adjustment in the effluent treatment plant addresses the sodium issue upstream in the brewery practically eliminating sodium from the effluent. In addition, a life cycle analysis (LCA) was carried out to assess the environmental impacts associated with the alternative cleaning and pH adjustment scenarios. The LCA showed that electricity consumption during use phase of the chemicals for respective purposes, as well as their production activities were major contributors to the significant environmental impact categories that were assessed. The cleaning scenario employing the use of hydrogen peroxide for both cleaning and disinfection was found to be the most environmentally sustainable. This was attributed to the reduced number of chemicals used compared to the other cleaning scenarios. Dolomitic lime was the pH adjustment alternative with the lowest average environmental impact; but, however, had a higher impact on freshwater eutrophication which is of major concern if the effluent will be reused for irrigation. Magnesium hydroxide was therefore considered to be the better option as a sodium hydroxide alternative for pH adjustment. This mitigates salt accumulation, making treated brewery effluent suitable for reuse in high value downstream agriculture and aquaculture, while employing more environmentally sustainable technologies. Notably, this converts brewery effluent from a financial liability to Ibhayi Brewery, into a product containing water and nutrients that generate income, improve food security, and can create employment in downstream agriculture and aquaculture in a sustainable manner. , Thesis (PhD) -- Faculty of Science, Ichthyology and Fisheries Science, 2021
- Full Text:
- Date Issued: 2021-10-29
Settlement and metamorphosis in the veliger larvae of the South African abalone Haliotis midae exposed to ambient grown biofilms treated with conspecific mucous
- Authors: Van Staden, Jefferson Luke
- Date: 2021-10-29
- Subjects: Haliotis midae , Biofilms , Haliotis midae Larvae Behavior , Haliotis midae Metamorphosis , Biosecurity , Aquaculture , Metamorphosis , Attachment mechanisms (Biology) , Mucous
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10962/192187 , vital:45203
- Description: The South African abalone, Haliotis midae, is a commercially important species of mollusc which contributes significantly to the value of the South African mariculture industry. One of the primary challenges experienced by abalone farmers is the consistent production of juvenile abalone (spat) in sufficient volumes to keep stocking farms and facilitate expansion of the industry. One of the key production bottlenecks of H. midae is achieving adequate levels of larval attachment and metamorphosis (settlement). The larvae of H. midae are settled on polycarbonate plates which have been pre-conditioned with biofilms in seawater which is pumped ashore onto farms. The seasonal variability in settlement success reported by hatchery managers in South Africa is hypothesised to be as a result of different diatom species compositions colonising the settlement plates at different times of the year, with settlement success being lowest during the winter months. The following study investigated whether the addition of conspecific mucous to biofilms could result in elevated settlement success, and whether there was potential for sterilisation of this mucous. A novel method of mucous application, spraying it onto the plates as opposed to pre-grazing, was tested in settlement assays and the trials revealed the following results: • The addition of H. midae mucous induced significantly more larvae to attach to settlement plates, when mucous was harvested around the spawning season. • Elevated attachment of larvae on mucous treated plates did not result in more post-larvae occupying the plates at the end of trials, and increased mortality is likely attributed to introduction of pathogens in conjunction with mucous. • No increase in the final proportion of settled larvae which had metamorphosed or the rate at which they metamorphosed was observed between mucous application treatments and biofilm only treatments. Subsequent trials assessed whether methods of mucous handling could reduce the biosecurity risk associated with mucous use, and so mucous was either UV irradiated or autoclaved. These trials revealed the following findings: • No difference in attachment was seen between any treatments, including the untreated mucous. This is contrary to the findings of our initial experiments and illustrates that the attachment-inducing properties within mucous may be seasonally expressed. ii • Numbers of observed larvae/post-larvae on plates applied with UV and autoclaved mucous where less stable than biofilms only, especially in the second trial, illustrating that mucous still presents a biosecurity risk even after undergoing these handling methods as it may act as a substrate on which pathogenic bacteria could colonise. , Thesis (MSc) -- Faculty of Science, Ichthyology and Fisheries Science, 2021
- Full Text:
- Date Issued: 2021-10-29
- Authors: Van Staden, Jefferson Luke
- Date: 2021-10-29
- Subjects: Haliotis midae , Biofilms , Haliotis midae Larvae Behavior , Haliotis midae Metamorphosis , Biosecurity , Aquaculture , Metamorphosis , Attachment mechanisms (Biology) , Mucous
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10962/192187 , vital:45203
- Description: The South African abalone, Haliotis midae, is a commercially important species of mollusc which contributes significantly to the value of the South African mariculture industry. One of the primary challenges experienced by abalone farmers is the consistent production of juvenile abalone (spat) in sufficient volumes to keep stocking farms and facilitate expansion of the industry. One of the key production bottlenecks of H. midae is achieving adequate levels of larval attachment and metamorphosis (settlement). The larvae of H. midae are settled on polycarbonate plates which have been pre-conditioned with biofilms in seawater which is pumped ashore onto farms. The seasonal variability in settlement success reported by hatchery managers in South Africa is hypothesised to be as a result of different diatom species compositions colonising the settlement plates at different times of the year, with settlement success being lowest during the winter months. The following study investigated whether the addition of conspecific mucous to biofilms could result in elevated settlement success, and whether there was potential for sterilisation of this mucous. A novel method of mucous application, spraying it onto the plates as opposed to pre-grazing, was tested in settlement assays and the trials revealed the following results: • The addition of H. midae mucous induced significantly more larvae to attach to settlement plates, when mucous was harvested around the spawning season. • Elevated attachment of larvae on mucous treated plates did not result in more post-larvae occupying the plates at the end of trials, and increased mortality is likely attributed to introduction of pathogens in conjunction with mucous. • No increase in the final proportion of settled larvae which had metamorphosed or the rate at which they metamorphosed was observed between mucous application treatments and biofilm only treatments. Subsequent trials assessed whether methods of mucous handling could reduce the biosecurity risk associated with mucous use, and so mucous was either UV irradiated or autoclaved. These trials revealed the following findings: • No difference in attachment was seen between any treatments, including the untreated mucous. This is contrary to the findings of our initial experiments and illustrates that the attachment-inducing properties within mucous may be seasonally expressed. ii • Numbers of observed larvae/post-larvae on plates applied with UV and autoclaved mucous where less stable than biofilms only, especially in the second trial, illustrating that mucous still presents a biosecurity risk even after undergoing these handling methods as it may act as a substrate on which pathogenic bacteria could colonise. , Thesis (MSc) -- Faculty of Science, Ichthyology and Fisheries Science, 2021
- Full Text:
- Date Issued: 2021-10-29
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