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
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- Date Issued: 2021-10-29
The optimisation of transportation methods for abalone (Haliotis midae Linnaeus, 1758 (Mollusca: Gastropoda)) larvae
- Authors: Bajaba, Sharone
- Date: 2021-02
- Subjects: Abalone fisheries , Haliotis midae , Abalone culture
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10353/20561 , vital:46124
- Description: Sea ranching has been identified as a viable method for enhancing the natural stock of overexploited abalone (Haliotis midae). Currently, this process involves transporting live juvenile H. midae to the seeding site where they are released onto the reef however this is both costly and logistically problematic. Transportation of abalone larvae is another cost-effective option, as they are cheaper to produce and can be transported at high densities. A suitable larval transport method is required to minimise larval mortalities and stresses that might compromise settlement. A series of simulated experiments were conducted to optimise transportation systems of abalone (Haliotis midae) larvae. First, two potential transportation modes (Wet (W) and Dry (D) transportation) conducted at a cooler (14˚C) and average ambient (18˚C) temperatures with six replicates of each were compared with control treatments (six replicates) that were not subjected to transport, kept in water at 18˚C. Eighty hours post-initial settlement, the 14W treatment had significantly lower settlement (p=0.03) than the other three treatments (14D, 18W, 18D) and the Control. The Dry method was the prefered method to transport larvae as it is logistically simpler to employ. The second experiment investigated the effect of different stocking densities (200, 400 and 800 larvae cm-2) for the Dry method 18˚C over two transit periods (six and twelve hours) on post-transport settlement and post-settlement survival of H. midae larvae. Compared to the control, there was no difference in the number of settled larvae (p=0.368) and larvae still swimming (p=0.835) across all treatments. This suggested that H. midae larvae can be transported for twelve hours at 800 larvae cm-2 without compromising post-transport settlement or survival. This study’s results and recommendations can be used by abalone farms when there is a need to move abalone H. midae larvae between farms or to seeding sites for sea ranching. Furthermore, other researchers can use these results as a benchmark for larval transportation studies of H. midae and other abalone species. , Thesis (MSc) (Zoology) -- University of Fort Hare, 2021
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- Date Issued: 2021-02
The effect of alginate supplementation on the growth, feed utilization, digestive enzyme activity levels, and intestinal morphology of juvenile South African abalone (Haliotis midae) fed formulated feeds
- Authors: Tlakedi, Thato
- Date: 2020
- Subjects: Abalones -- Feeding and feeds -- South Africa , Haliotis midae , Abalones -- Digestive organs , Abalones -- Morphology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/145279 , vital:38424
- Description: Alginate occurs abundantly in kelp and while a few studies have quantified the effect of kelp inclusion in formulated Haliotis midae feeds, none have researched the effect of alginate inclusion on the growth of abalone fed this feed. Feeding kelp to cultured abalone affects gut structure and modulates gut bacteria, aiding digestion by upregulating enzyme activity. This farm-based experiment compared the growth, feed utilization, digestive enzyme activity levels and intestinal villi structure between abalone (1-year-old, 10 - 20 mm shell length) fed kelp-supplemented (BK) or alginate-supplemented (BA) diets and abalone fed basal (B) and fresh kelp (K) diets for a period of eight months from June 2017 to February 2018. Growth and enzyme activities were also compared between abalone that experienced dietary changes and abalone that remained on their initial diets. The tested diets were: base diet (B, 34% protein), the same base diet supplemented with fresh minced kelp (0.90% kelp [dry mass, equivalent to 0.20% alginate]; BK), base diet supplemented with sodium alginate (0.20% alginate; BA) and a fresh kelp diet (K). Alginate or kelp inclusion in a formulated feed had no significant effect on the specific growth rates (SGR), linear shell growth rates (LGR), daily percentage feeding rates (PFR), feed conversion ratio (FCR), percentage mass gain (MG) and condition factor (CF) over the eight month trial period, compared to abalone fed the base diet. In October 2017, four months since the start of the trial in June, all the groups fed formulated feeds showed significantly higher average weight gain (8.42 ± 0.72 g to 8.86 ± 0.63 g) compared to the kelp-fed group (6.68 ± 0.43 g). However, no significant differences in the average weight gain were observed between abalone fed kelp and formulated feeds at the end of this study. Furthermore, there were no significant differences in the FCR and PFR between abalone fed the base or alginate diets and abalone fed the fresh kelp diet. However, the SW diet produced significantly lower FCR (1.00 ± 0.13) and PFR (0.78 ± 0.10%) compared to the kelp diet (10.6 ± 1.40% and 8.12 ± 1.01%, respectively). All formulated diets produced non-significant LGR, MG and CF compared to the kelp diet at the end of this study. Enzyme activity levels were compared between abalone fed the test diets in July and August 2017 and February 2018. There were no significant differences in the average alginate lyase specific activity levels between abalone fed formulated diets in July and August 2017. At the end of the trial, however, the alginate diet induced significantly higher alginate lyase specific activity levels (4.89 ± 1.64 mg.mg-1 protein) compared to the base diet (1.57 ± 0.98 mg.mg-1 protein), but showed no significant differences compared to the SW (3.78 ± 0.41 mg.mg-1 protein) and fresh kelp-only diets (4.00 ± 0.62 mg.mg-1 protein). The SW diet showed no significant differences in the alginate lyase specific activity levels compared to the base diet. There were no significant differences in the chymotrypsin activity levels between the test diets throughout this study. Alginate or kelp inclusion also had no significant effect on the intestinal structure compared to the base or fresh kelp diets. This was despite a higher degree of variability in microvilli height and width being observed in abalone fed the kelp-only diet, with microvilli visibly wider and longer than in abalone fed formulated feeds. Switching abalone between some diets significantly affected the average weight gain, MG, FCR and PFR, alginate lyase, chymotrypsin and cellulase activity levels compared to abalone kept on their initial diets. The inclusion levels of kelp and alginate used in this study were likely too low to affect abalone growth as higher inclusion levels, particularly of alginate, have been found to improve fish growth. This study concluded that minced kelp and alginate inclusion in a formulated H. midae diet did not affect the SGR, FCR and intestinal morphology, but significantly affected alginate lyase and chymotrypsin activity levels. Furthermore, changes in growth and digestive enzyme activity levels coincided with dietary changes. Consequently, higher inclusion levels, particularly of sodium alginate, and the effect of dietary changes on abalone growth and digestive enzymes must be investigated in future studies.
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- Date Issued: 2020
Aspects of the nutritional physiology of the perlemoen Haliotis midae (L.) and red abalone H. rufescens (Swainson)
- Authors: Kemp, Justin Oliver Gordon
- Date: 2018
- Subjects: Haliotis midae , Haliotis midae fisheries , Red abalone , Haliotis midae -- Feeding and feeds , Red abalone -- Feeding and feeds , Haliotis midae -- Nutrition -- Requirements , Red abalone -- Nutrition -- Requirements , Haliotis midae -- Metabolism , Red abalone -- Metabolism , Haliotis midae -- Physiology , Red abalone -- Physiology , Stable isotopes , Algae as feed
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/62314 , vital:28154
- Description: The source of abalone for human consumption has shown a dramatic shift away from wild-capture fisheries in the last 30 years, with over 90% of global production now coming from aquaculture. Farmers initially relied on the natural food of abalone (macroalgae) as a culture feed, though in regions where macroalgae availability was limiting, the need to develop formulated feeds was evident. Extensive research effort has led to the development of a number of formulated feed products currently employed in the industry. These feeds, however, differ markedly from the mixed macroalgal diets that abalone have evolved to utilise, particularly in terms of protein content and carbohydrate structure. The degree to which the nutritional physiology of abalone responds to these novel formulated diets, with and without macroalgal supplementation, was investigated in the current study. A multifaceted approach, combining growth trials, stable isotope nutrient tracers and metabolic experiments, was employed to gain insight into the post-absorption dynamics and utilisation of dietary nutrients under varying dietary regimes of fresh macroalgae and formulated feed. Growth trials conducted with both Haliotis rufescens and H. midae showed significantly higher growth and protein utilisation efficiency for abalone fed macroalgal diets compared to formulated feeds. Furthermore, when formulated feeds were supplemented with macroalgae to form combination diets, growth and the utilization of protein was improved compared to the formulated-feed-only diet. The poor utilisation of protein by H. midae fed the formulated feed could be traced, using a method combining stable isotope bio-markers with a Bayesian mixing model (SIAR), to the low incorporation of the fishmeal component of protein in the diet. The marked postprandial drop in the O:N ratio on abalone fed formulated feeds indicate that the protein was being diverted into catabolic metabolic pathways. The metabolic cost of digestion, termed specific dynamic action (SDA), was negated as a factor in the improved growth of abalone fed macroalgal diets, with the SDA coefficient 2.1 times that observed for formulated feed. Furthermore, the postprandial haemolymph glucose concentration (HGC) in H. midae was elevated when fed formulated feed compared to macroalgae. The high levels of circulating glucose are likely a result of the structure the carbohydrate source in formulated feeds and stimulate the deposition of glycogen through the allosteric control of glycogen synthase. Formulated feeds produced higher cooked meat yields in canning simulation trials, suggesting that muscle glycogen content may indirectly play a role in increasing canning yields through the displacement of collagen. The results of these empirical studies are synthesised under key themes, discussed within the context of their potential commercial relevance and future research directions are highlighted.
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- Date Issued: 2018
The effects of dietary soya and crystalline phytoestrogens on the growth, gonad development and histology of farmed abalone, Haliotis midae
- Authors: Wu, Yu
- Date: 2015
- Subjects: Haliotis midae , Haliotis midae -- Feeding and feeds , Haliotis midae -- Growth , Haliotis midae -- Histology , Haliotis midae -- Effect of chemicals on , Soybean as feed , Phytoestrogens
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5380 , http://hdl.handle.net/10962/d1017225
- Description: The inclusion of soya as a dietary protein source in the formulated feed, Abfeed® S34 (Marifeed Pty (Ltd), Hermanus) for farmed abalone, Haliotis midae has resulted in larger gonads during reproductive seasons compared to the gonads of abalone fed kelp or diets that included fishmeal as the only main protein source. The aim of this study was to determine if the isoflavones present in the soya were responsible for this increase in gonad size and the subsequent effects on farmed abalone growth. Animals weighing between 40-50 g were fed one of seven isonitrogenous and isoenergetic diets containing either 0, 25, 50 or 100 percent of the soya component of the commercial feed (Abfeed® S34, Marifeed Pty (Ltd), Hermanus) from September 2013 to March 2014. An additional three diets were formulated to include crystalline isoflavone (ISO). These diets were identical to the 0 percent soya diet (i.e. the fishmeal only diet - FM), only ISO was included at the same rate that ISO occurred in the three soya diets. Data were analysed using a multiple forward stepwise regression analysis (MSR) to test the effects of ISO concentration, soya concentration, time, sex, time by concentration interaction and sex by concentration interaction on growth and gonad development and to identify those variables that most contributed to the model. The inclusion of crystalline ISO failed to promote larger gonads and had no effect on abalone growth, while growth and gonad development was dose dependent on soya inclusion rates with sex and time contributing to the models. Mean monthly weight gain in males correlated with increasing soya concentrations (c) (MSR, y = 3.24 + 0.002c, r2 = 0.23, p = 0.03), ranging from 3.11 ± 0.55 g abalone-1 month-1 to 4.43 ± 0.46 g abalone-1 month-1, while both male and female monthly length gain was not influenced by soya concentration with an overall mean of 1.62 ± 0.05 mm abalone-1 month-1 (MSR, p = 0.05 and p = 0.81, respectively). By December, the whole body mass, meat mass and visceral mass in both males and females decreased with increasing soya levels. However, by February, female whole body mass, meat mass and visceral mass positively correlated with soya levels. At the end of the study, male abalone fed FM with soya equivalent to the commercial feed had the highest whole body mass (69.00 ± 2.48 g abalone-1), meat mass (41.80 ± 1.12 g abalone-1), visceral mass (9.00 ± 2.47 g abalone-1) and gonad bulk index (42.70 ± 9.82 g abalone-1), while females were not influenced by soya concentrations with an overall whole body mass of 63.46 ± 0.79 g abalone-1. Weight loss was observed in all treatments between February and March, probably due to a spawning event. The moisture content in the meat was not influenced by treatment, however, visceral water loss was effected by both ISO and soya concentration with time and sex contributing to the model. The visceral water loss of females fed graded levels of soya decreased as a function of soya from December to March, and from December to February for males, whereas females fed ISO-enriched diets decreased as a function of ISO concentration (c) at the end of the study from 74.98 ± 0.88 to 73.10 ± 0.75 percent (MSR, y = 74.97 – 0.0025c, r2 = 0.20, p = 0.048). The inclusion of crystalline ISO had no significant effect on oogenesis in female farmed Haliotis midae, while the distribution of the predominant oocyte stage, stage 7 (second last stage prior to spawning) was dose-dependent in abalone fed increasing soya concentration (c) (MSR, y = 33.38 + 0.03c, r2 = 0.32, F(1, 18) = 8.52, p = 0.01). The increase in stage 7 oocytes in abalone fed FM with soya did not reduce the number of oocytes (44.96 ± 3.01 oocytes mm-2) present within the lumen, while the number of oocytes (o) in abalone fed the FM-only based diets decreased with increasing abundance of stage 7 oocytes (MSR, y = 58.28 – 0.48c, r2 = 0.38, F(1, 18) = 12.51, p = 0.002), possibly due to the increase in size of the oocytes with thicker jelly coats. This study provided evidence that crystalline isoflavone had no influence on abalone gonad development over five months, while soya had a dose-dependent effect on growth, gonad mass and oogenesis in farmed Haliotis midae. Formulated abalone feed could be manipulated at certain times of the year to obtain maximum growth. These implications and further studies were discussed.
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- Date Issued: 2015