Apparent digestibility coefficients of feed ingredients and essential amino acid requirements of dusky kob (Argyrosomus japonicus)
- Authors: Adesola, Abidemi Adejoke
- Date: 2017
- Subjects: Amino acids in animal nutrition , Fishes -- Feeding and feeds , Argyrosomus japonicus , Argyrosomus , Argyrosomus japonicus -- Nutrition , Argyrosomus -- Nutrition , Argyrosomus japonicus -- Feeding and feeds , Argyrosomus -- Feeding and feeds
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/32140 , vital:24014
- Description: Important to the evaluation of potential feed ingredients for inclusion in fish diets should be their digestibility and amino acid requirement so that feeds can be formulated on a digestible basis rather than a gross nutrient basis. This thesis established techniques for faecal collection, the validity of digestibility markers, it determined apparent digestibility coefficients for various novel feed ingredients, and it established the optimal lysine requirement for Argyrosomus japonicus, which was used to estimate each of the essential amino acid requirements by using the ideal protein concept. There were no significant differences in dry matter apparent digestibility coefficients when faeces were collected by stripping (77.0 %), dissection (80.1 %) or settlement (83.5 %). Faecal collection by the settlement method produced the most reliable digestibility data. Apparent digestibility coefficients for dry matter, crude protein and energy calculated using acid-insoluble ash were higher (84.0 %, 93.2 % and 93.0 %, respectively) than those using chromic oxide (55.7 %, 79.1 % and 78.2 %) and titanium dioxide (58.6 %, 79.7 % and 80.5 %). The magnitude of variation in digestibility coefficients obtained using acid-insoluble ash was always lower than that obtained with the other markers. Therefore, acid-insoluble ash was preferred as a dietary marker. Using the above protocol, protein and amino acid digestibility of some animal and plant protein ingredients were evaluated in a series of experiments. The first trial compared the apparent digestibility coefficients of some animal products included as single protein source in the test diets. Apparent protein digestibility values were 84.5 %, 83.8 %, 85.8 % and 83.1 % for fishmeal-prime, fishmeal-standard, poultry meal and pork meal, respectively. Apparent digestibility coefficients for poultry meal were comparable to those of fishmeal, which indicate its potential as a substitute for fishmeal in the diets of A. japonicus. The second trial determined the apparent coefficients of plant and animal protein sources included at 30 % into a practical reference diet (70 %). Apparent protein digestibility ranged from 92.4 % in sunflower meal to 85.5 % in corn gluten meal. Soybean meal is a promising feed ingredient in A. japonicus due to the high apparent digestibility of its protein (92.0 %) and essential amino acid digestibility (mean average 91.4 %). A fundamental assumption in fish feed formulation is that the digestibility of nutrients is additive, i.e., digestibility of a nutrient in one ingredient does not interact with the digestibility of the same nutrient in another ingredient. In the third trial, additivity of feed ingredients was tested using pork meal and poultry meal. The results indicate that the apparent digestibility coefficient of animal protein ingredients could be calculated from compound diets to accurately determine protein and amino acid digestibility in A. japonicus, and possibly other carnivorous fish species. Dietary essential amino acid requirements were determined for juvenile A. japonicus in two trials. A dose-response study was conducted using crystalline lysine to determine the optimal requirement of dietary lysine for A. japonicus. Optimal dietary lysine was estimated at 31.7 g kg-¹ dry diet, corresponding to 73.5 g kg-¹ of dietary protein, based on specific growth rate and broken-line segmented regression analyses. Dietary requirements for other essential amino acids ranged from 22 g kg-¹ (histidine) to 71 g kg-¹ (leucine) crude protein. The results of the present study provided a research tool that could be used to assess and verify the conclusions of earlier dietary work on A. japonicus and in further studies to develop least cost diet formulations for this species. The study also adds to the knowledge of the nutritional requirements of A. japonicus by providing information on the digestibility of plants and animal protein ingredients. It also contributes to future dietary research for this species because this study determines, for the first time, the most suitable methods for investigating the digestibility of raw materials for A. japonicus.
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- Date Issued: 2017
The effect of carbohydrate on dusky kob, Argyrosomus japonicus, fed pelleted diets
- Authors: Mabasa, Nyiko Charity
- Date: 2017
- Subjects: Carbohydrates in animal nutrition , Fishes -- Feeding and feeds , Argyrosomus japonicus , Argyrosomus , Argyrosomus japonicus -- Nutrition , Argyrosomus -- Nutrition , Argyrosomus japonicus -- Feeding and feeds , Argyrosomus -- Feeding and feeds
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/44895 , vital:25450
- Description: The dusky kob, Argyrosomus japonicus, is an emerging commercial marine aquaculture species in South Africa. Attributes such as market acceptance, fast growth rates, tolerance to sibling density, acceptance of pelleted feed and adaptability to intensive aquaculture conditions make it a good candidate. Feed, the largest running cost in most aquaculture operations, is a limiting factor in dusky kob production as its nutritional requirements are not well understood. The present project formed part of a research program to develop a locally produced, least cost and sustainable feed that will support the growth and health of dusky kob. The approximate protein and energy requirements for kob fed formulated feeds have been established in earlier research, but the ability of kob to utilize carbohydrates as an energy source has not previously been investigated. The aim of this study was to determine the efficiency of dusky kob to utilize graded levels of carbohydrate (pregelatinized maize starch - PGMS) in pelleted diets. The research objectives were to determine the effect of dietary carbohydrate levels on:i) growth and feed utilization; ii) post prandial blood glucose levels; and iii) general fish health, gut bacterial composition and liver glycogen content of juvenile dusky kob. Hatchery reared juvenile dusky kob (5 g) were acclimatized in a recirculating experimental aquaculture system at the Department of Ichthyology and Fisheries Science at Rhodes University. They were fed trout crumble starter feed for three weeks before the start of the feeding experiment. Five diets containing 4.1, 8.2, 16.4 and 24.6% carbohydrate, hereafter referred to as 4.1C, 8.2C, 16.4C and 24.6C respectively, were formulated with pregelatinized maize starch as a carbohydrate source and fishmeal as the main protein source. Fish were fed these diets twice daily at 3.85% body weight per day for three months. Specific growth rates and feed conversion rations differed significantly between the four dietary treatments. Growth rate increased with increasing carbohydrate up to 16.4%, after which a significant decline was observed. Diet 16.4C produced the highest specific growth rate (SGR) of 1.84 ± 0.05% body weight/day, and the lowest feed conversion ratio of 1.28 ± 0.08. While the lowest specific growth rate and highest feed conversion ratio of 0.79 ± 0.05 and 2.14 ± 0.13 respectively, were found for diet 24.6C. A third order polynomial regression, using SGR, determined the optimum carbohydrate inclusion for dusky kob to be 16.72%. The general structure of the liver was similar between all fish fed the dietary treatments and all fish liver samples displayed a certain degree of lipid vacuolization of the hepatocytes. Evidence of starvation was observed in the livers of fish fed diet 24.6C. However, no differences in the amount of liver glycogen were observed. Gut bacterial composition did not differ among the different diets or between the different sections of the gut. Differences were however observed in the diversity of the bacterial community structure at the start (when they were fed commercial trout feed) and end of the experimental period (after being fed a fishmeal-maize diet). The rate at which glucose was cleared from the blood differed significantly between diets. The low carbohydrate diets (i.e. diet 4.1C and 8.2C) showed a steady rate of glucose removal from the blood over a 48 h experimental period. Sharp increases in blood glucose concentration were observed in diet 16.4C and diet 24.6C, with highest glucose concentrations of 7.18 ± 1.81 and 8.05 ± 2.35 mmol/l respectively, observed 24 h after feeding. The blood glucose concentration of the fish fed diet 16.4C however returned to resting glucose concentration after 48 h, while that of the fish fed diet 24.6C did not. The results demonstrated that the level of dietary carbohydrate inclusion has a significant effect on the growth and health of the fish. The optimum carbohydrate inclusion in dusky kob diets is indicated to be 16.7%, which gave the best growth rate and maximum protein sparing effect without adverse effects on fish health. These findings are important for diet formulation and producing ‘least-cost’ diets for dusky kob farming.
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- Date Issued: 2017
The development of a practical diet for juvenile dusky kob, Argyrosomus japonicus, for the South African mariculture industry
- Authors: Woolley, Lindsey
- Date: 2009
- Subjects: Fishes -- Nutrition -- Requirements , Fishes -- Food , Fishes -- Growth , Fish culture , Argyrosomus -- Nutrition , Sciaenidae -- Nutrition
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5257 , http://hdl.handle.net/10962/d1005100 , Fishes -- Nutrition -- Requirements , Fishes -- Food , Fishes -- Growth , Fish culture , Argyrosomus -- Nutrition , Sciaenidae -- Nutrition
- Description: The lack of locally manufactured marine finfish diets motivated the current project, which aimed to develop a practical diet specifically formulated for dusky kob. The first growth trial investigated the effect of pellet texture (i.e. hard versus soft pellets) and the inclusion of an additional binder, test treatments were compared to two reference diets. There was no significant difference in weight gain between fish fed the hard or soft pellets (p=0.17), over nine weeks. The fish fed the local trout feed weighed significantly less than those fed the test diets (p=0.003). There was no significant difference in leaching rate amongst treatments (p=0.45). A hard pelleted diet without gelatin is recommended in the commercial culture of dusky kob. Pellets with different physical shapes were tested to determine the effect of shape on settling speeds. A square shaped pellet had a slower sinking rate compared to a round shaped pellet (p<0.0001). Juvenile dusky kob, held in cages, fed the square pellets grew significantly faster than the fish fed the round pellet, with a mean weight gain of 16.81 ± 0.45 g (p=0.018). A growth trial was used to optimize the protein to energy (PE) ratio by adjusting dietary protein and lipid levels. Fish fed the diets with high levels of protein (46 % protein) achieved the better growth rates (125 % weight gain) compared to the lower protein diets (92 % weight gain) (p<0.0001). There was no significant difference in total ammonia production (TAN) level for the 46 and 42 % protein diets (p=0.68). The overall performance of the prototype diet was investigated in a closed recirculating system. Growth and FCR of the fish fed the prototype diet was on a par to those fed the commercially available diet currently used in the local farming industry. There was no significant difference in the blood chemistry for fish held at increased stocking densities. The prototype diet is suitable for use in recirculating systems, as there were no negative effects on water quality parameters. This study has laid a foundation for the manufacture of a practical commercial dusky kob diet in South Africa.
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- Date Issued: 2009