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1.
In many countries, aquaculture development has been driven by technical solutions to the culture of high unit value (HUV) species. As rising production has met with falling prices, diversification into other HUV species has occurred and renewed the 'speciescycle’process. However, if aquaculture is to make its forecast contribution to offset declining capture supplies, some redirection may be needed to determine the substitute species and the product profile sought by consumers, and hence, the areas for genuine opportunity for growth. To this end, this paper employs Multiple Correspondence Analysis (MCA) to analyse consumer acceptance of a cultured product. The MCA identifies patterns of association hidden by conventional techniques and may provide a methodology for identifying more relevant responses by the international aquaculture industry to the needs of the market. To illustrate the potential, the paper presents a case study of African catfish, Clarias gariepinus (Burchell 1822), using face-to-face consumer surveys incorporating samples of Clarias fillets in household meals. The MCA suggests that the Clarias product has attributes which are not uniquely orientated to any particular niche market, in contrast to most conventional HUV species. This may be advantageous, and for example, suggests that Clarias might be marketed as frozen blocks for further added value products and as a substitute for those demersal species which are less available internationally.  相似文献   

2.
Understanding the major causes of growth variation is crucial for the success of fish farming since its reduction contributes to maximize production efficiency, reduce food waste and improve water quality. The growth variation observed in aquaculture has been associated with the establishment of social hierarchies. However, some studies suggest that this variation may not be mainly a consequence of social hierarchies but mainly a result of inherent (genetic) differences. This study investigates the magnitude of individual responses, independently of group effects (fish housed individually), in growth efficiency and feeding behaviour of African catfish Clarias gariepinus (Burchell 1822). Despite the low variation in initial body weight (6.5%) and cumulative feed consumption (7.5%) over the experimental period, catfish exhibited high variation in final body weight (18.1%), specific growth rate (17.2%) and feed conversion ratio (27.9%), suggesting that individual variation in growth efficiency is important in determining growth rate. This individual variation may be related with individual differences in protein/fat deposition since faster growing fish deposited more protein and less fat than slower growing fish. Pronounced individual differences in feeding behaviour (reaction towards feed and time spent eating) were also observed and correlated with individual differences in growth efficiency. Fast eaters were the fast growers. We suggest that the growth variation observed in African catfish may be inherent and that the use of grading to increase uniformity should be further investigated.  相似文献   

3.
There is a difficult path to tread between strictly accurate scientific nomenclature, which definitively and clearly characterizes exact developmental stages, and the vernacular names popularly used in the fish culture industry. On the one hand, the recognition of early life stages by the culturist is important because the requirements of young fish change rapidly with age (e.g. Hogendoorn 1980; Verreth & Van Tongeren 1989). On the other hand, recognition of microscopic changes can be more subjective than definitive and may be of no actual benefit in fish culture. Working definitions of developmental stages for aquaculture are therefore most usefully practical ones. In response to calls for a clear definition regarding the length of the larval period, in order to enhance the compatibility of different studies (Verreth & Van Tongeren 1989), the following definitions for African catfish, Clarias gariepinus (Burchell) are suggested.  相似文献   

4.
Inland fisheries play important roles in food and economic security in the riparian countries surrounding the Great Lakes of Africa. However, the lakes are being systematically degraded by anthropogenic pressures, in combination with the huge population growth prevalent in the region. This paper summarises the outcomes of an international conference to develop a ‘Strategy for Conservation and Sustainable Development of the African Great Lakes Region in a Changing Climate’, held in Uganda in 2017, with particular attention on the potential for fisheries and aquaculture. The paper highlights options for addressing the problems facing the aquatic resources and specifically the importance of effective management of the fisheries and ecosystems of the Great Lakes to achieving the UN Sustainable Development Goals to ensure food and nutritional security and sustainable livelihoods. There is need to improve fisheries assessment and determine the value of the fisheries (and aquaculture). Fisheries legislation, regulation and enforcement need revision and co‐management mechanisms require rethinking. There is considerable potential for aquaculture, and especially cage culture, to increase fish production, but there is an urgent need to address technical, social, environmental and input requirements. It is also imperative that best practices guidelines are developed that will support cage culture production practices.  相似文献   

5.
Total ammonia and total nitrogen efflux rates of the African catfish, Clarias gariepinus (Burchell), were measured under different temperature conditions (20, 25 and 30°C) and feeding regimes (50% protein, 40% protein and non-fed for 10 days). Both ammonia and nitrogen efflux rates were directly related to temperature. At all experimental temperatures, the 50%-protein-fed groups excreted higher levels of ammonia nitrogen than both the 40% protein and non-fed groups. No correlation of relative ammonia efflux (% ammonia/nitrogen) with either temperature or diet was observed under these experimental conditions. Such alterations caused by temperature and diet may have significant implications for an aquaculture system as low levels of dissolved ammonia are synonymous with optimum water quality.  相似文献   

6.
Brine shrimp Artemia, the most common live food organism used in larviculture, can reproduce either oviparously (production of dormant cysts) or ovoviviparously (direct production of nauplii), depending on environmental conditions. Ovoviviparous Artemia nauplii have seldom been considered as a source of live food in aquaculture, partly due to the convenience and the developed techniques associated with the production and use of the dormant cysts. In many countries in Africa, however, hatchery managers do not have access to a reliable supply of affordable good quality cysts. In this study, we therefore demonstrated the potential of a system designed for the continuous ovoviviparous production of nauplii at low salinity, using Great Salt Lake Artemia franciscana and micronized agricultural material as feed. The suitability of the produced nauplii was tested by feeding them directly to Clarias gariepinus larvae in comparison with oviparous nauplii and decapsulated cysts. Higher survival (100%), better protein efficiency ratio (2.6 ± 0.1) and food conversion ratio (1.0 ± 0.1) was observed in larvae fed with the ovoviviparous nauplii (p < 0.05). Overall, we conclude that the ovoviviparous nauplii could serve as an alternative live food for larval fish. If optimized, the system could be validated for integration in hatcheries.  相似文献   

7.
Abstract. The African catfish, C. gariepinus (Burchell), a candidate species for aquaculture in southern Africa, is frequently infested by the branchiuran ectoparasite Dolops ranarum. Normal integument, as well as damage caused by this parasite, is described by means of scanning electron microscopy and histology. Wound healing and the attachment and feeding mechanism of the parasite is described.  相似文献   

8.
The nitrite threshold concentration in rearing water of African catfish (Clarias gariepinus) was assessed. African catfish with an initial mean (SD) weight of 219.7 (57.8) g were exposed to an increasing range of water nitrite from 6 (Control) to 928 μM nitrite for 28 days. Mean (SD) plasma nitrite concentrations increased from 5.0 (3.6) to 32.5 (12.6) μM at 928 μM ambient nitrite. The increase in nitrite was accompanied by gradual increase in plasma nitrate from 41.6 (28.4) μM to 420.2 (106.4) μM. Haematocrit, haemoglobin, methemoglobin, plasma concentrations of cortisol, glucose, lactate, osmolality, gill morphology and branchial Na+/K+‐ATPase activity were not affected. Feed intake, final weight, SGR, FCR and mortality were not affected. We advise not to exceed a water nitrite concentration of 43 μM (0.6 mg L?1 NO2?‐N) to prevent the risk of reduced growth and feed intake in African catfish aquaculture.  相似文献   

9.
The nitrate threshold concentration in rearing water of African catfish (Clarias gariepinus) was assessed. Female African catfish with an initial mean (SD) weight of 154.3 (7.5) g were exposed to 0.4 (Control), 1.5, 4.2, 9.7 and 27.0 mM nitrate for 42 days. Mean (SD) plasma concentrations of nitrate increased from 71 (29) to 6623 (921) μM at the highest ambient nitrate level. Mean (SD) plasma nitrite concentration ranged from 1.2 (0.5) to 7.9 (9.0) μM. Haematocrit, plasma concentrations of non‐esterified fatty acids (NEFA), cortisol, glucose, lactate, osmolality, gill morphology and branchial Na+/K+‐ATPase activity were not affected. Feed intake and specific growth rate were significantly reduced at the highest nitrate concentration. We advise not to exceed a water nitrate concentration of 10 mM (140 mg L?1 NO3‐N) to prevent the risk of reduced growth and feed intake in African catfish aquaculture.  相似文献   

10.
Semi-purified diets containing 39% crude protein and 5% lipid were used to identify the qualitative requirement of African cattish, Clarias gariepinus (Burchell), for niacin and to characterize the pathologies associated with a deficiency of this vitamin. After 48 days of feeding, C. gariepinus supplied with the unsupplemented diet had developed severe deficiency symptoms and were subsequently withdrawn from the growth study. Niacin deficiency was characterized by feed refusal, listlessness, weight loss, poor feed utilization and high mortality. The skin overlaying the lateral line of the deficient fish became haemorrhagic and this clinical sign was accompanied by severe anaemia. After 126 days of feeding, fish fed diets containing 17.0 mg niacin kg?1 had also developed a dermopathy. but without anaemia or high mortality. The feeding of diets containing less than 33.1 mg niacin kg?1 resulted in suboptimal feed efficiency and poor protein utilisation. Allometric analysis of proximate composition indicated that carcass moisture, protein and ash were influenced by fish size, and not by dietary niacin content. However, significantly more lipid per unit of weight gain was deposited in the carcasses of fish fed the unsupplemented diet than in fish fed diets containing 17.0mgkg?1. The indicators used in the present study could not be applied to accurately determine a value for niacin requirement. However, until a more accurate assessment is performed, it is recommended that diets for C. gariepinus contain not less than 33.1 mg nicotinic acid kg?1 feed.  相似文献   

11.
Abstract In order to promote the successful supply and satisfactory survival of African catfish, Clarias gariepinus (Burchell), it is advocated that the fish be reared in hatcheries until they begin air breathing. Research conducted over a number of years to develop culture technology for intensive hatchery rearing to the stage of air breathing is brought together here as an overview. In particular, the definition of early development stages is considered as well as induced spawning, egg incubation, larval rearing and fry rearing.  相似文献   

12.
The abalone, Haliotis midae (commonly referred to as “perlemoen”), is an important aquaculture species in South Africa, accounting for the highest percentage of total aquaculture production revenue. The industry largely makes use of wild, undomesticated broodstock and thus a consortium of top producers was formed to develop a genetic improvement program to increase efficiency and sustainability of the industry. As such, the current study aimed to evaluate growth trait performance (wet weight and shell length) of four hatchery‐derived cohorts of South African abalone, across four differing production environments. No significant cohort‐by‐location effects were found for weight and length traits; however, differences were detected between respective cohorts and locations. It is concluded that a single synthetic population comprised of all hatchery cohorts under a single breeding goal is suitable for production at all test locations. Furthermore, advances in artificial reproductive technologies, genetic markers, and individual identification hold promise for genetic improvement of the species.  相似文献   

13.
Abstract. In fish larvae there is a strong natural selection for high yolk utilization efficiencies and high yolk absorption rates. Larvae with higher absorption and utilization will be larger at the onset of exogenous feeding, leading to higher survival and growth rates in the following stages of development. Modelling can be a powerful tool in clarifying the processes of fish larvae metabolism, providing the model is as explanatory as possible. The present model considers the larvae as a two-compartment system: the yolk sac and the larval body. This system exchanges oxygen, carbon dioxide, water, ammonia and heat with the environment. Yolk is absorbed through the syncytium, digested, and the resulting nutrients are released into the blood circulation. Circulating amino acids and fatty acids are considered to be used first for respiration, and what is left will be used for growth. From the moment that absorbed nutrients do not satisfy the energy needs, embryo tissue starts to be catabolized. Temperature is the only environmental factor which was assumed to affect significantly the metabolic processes. From the comparisons between simulations and experimental data, the simulations would appear to be accurate until complete yolk absorption, losing accuracy afterwards. Simulation outputs suggest that fat is the main energy substrate during yolk absorption, with protein becoming progressively more important, being predominant during starvation. Ideal culture conditions for African catfish yolk sac larvae seem to include: the highest temperature that combines with acceptable mortality rates; selection of broodstck towards obtaining the largest egg size, insofar as viability is not affected; the start of feeding as close as possible to 144 physiological day-degrees.  相似文献   

14.
Dietary histidine requirement of fry African catfish, Clarias gariepinus (2.57 ± 0.02 cm; 0.22 ± 0.03 g) was quantified by feeding casein–gelatin-based isonitrogenous (40% crude protein) and isocaloric (17.90 kJ g−1 gross energy) amino acid test diets with graded levels of histidine (0.25%, 0.30%, 0.35%, 0.40%, 0.45% and 0.50% dry diet) in eighteen 80 L indoor circular aqua-coloured troughs provided with the flow-through system for 12 weeks. Maximum absolute weight gain (2.66), best feed conversion ratio (1.29), highest protein efficiency ratio (1.94), protein retention efficiency (34%) and energy retention efficiency (70.4%) were achieved at 0.40% dietary histidine. Broken-line and non-linear regression models were adopted to assess dietary histidine requirement for C. gariepinus . When analysed using broken-line regression model these parameters were also best at 0.40% dietary histidine corresponding to 1.0% protein, respectively, whereas using second-degree polynomial regression analysis, histidine requirement was obtained at 0.42%, 0.41%, 0.40%, 0.41% and 0.41% of dry diet, corresponding to 1.05%, 1.02%, 1.0%, 1.02% and 1.02% protein respectively. Based on the broken-line and second-degree polynomial regression analyses of the growth and nutrient retention data, optimum histidine requirement of fry C. gariepinus was found to be in the range of 0.40–0.42% dry diet, corresponding to 1.0–1.05% of dietary protein.  相似文献   

15.
为研究絮团浓度对革胡子鲇零换水养殖效果的影响,在不额外添加有机碳源（只利用饲料中的碳）的革胡子鲇（）养殖系统中,设置了平均絮团质量浓度为561.18 mg/L和780.41 mg/L两个处理组,比较了两实验组的水质、菌群结构、鱼生长及氮利用效率。结果表明,两种浓度絮团条件下,总氨氮（total ammonia nitrogen,TAN）和亚硝酸氮（NO2--N）能分别维持1.84 mg/L和1.79 mg/L以下。两处理组间pH、溶解氧（dissolved oxygen,DO）、TAN、NO2--N、氮素利用效率及主要生长指标无显著差异（-N）浓度（822.0 mg/L）明显高于低浓度絮团组（623.33 mg/L）。高通量测序分析菌群结构结果表明,两组间门水平的菌群组成种类及优势度无显著性差异（<0.05）。两处理组中的革胡子鲇存活率分别达到（91.11±1.53）%和（94.44±2.08）%,饲料系数为（1.41±0.18）和（1.27±0.26）,特殊生长率为（2.13±0.04）%/d和（2.19±0.08）%/d,均无显著差异（>0.05）。两实验组饲料氮的利用率分别达到了72.17%和71.34%。综合以上结果认为,仅利用饲料中的碳既能维持革胡子鲇的零换水养殖且能取得较高的氮素利用效率,两种絮团浓度对革胡子鲇的生长无显著影响,高浓度絮团组中的硝化作用更明显。  相似文献   

16.
The value of toasted Mucuna utilis seed meals was investigated in this study by evaluating the nutritional profile and the utilization of the processed seeds in isonitrogenous (35% CP) and isocaloric diets (17 kJ g?1) for African catfish Clarias gariepinus (Burchell 1822). Toasting the M. utilis seed significantly reduced the levels of tannins, phytate, trypsin, and hemagglutinin in the seeds. However, protein, gross energy, arginine, histidine, and valine were increased (P ≤ 0.05). The processed seed was then used to formulate five experimental diets by progressively increasing its inclusion (by 50 g kg?1) from zero up to 200 g kg?1. A sixth diet was also formulated with raw M. utilis included at 200 g kg?1 to determine the efficacy of the processing method applied in this study. Fifty fingerlings of C. gariepinus (2.02 g ± 0.08) stocked in 18 hapas measuring 1 × 1 × 1 m3 were then fed the diets for 56 days. The growth of C. gariepinus fingerlings was significantly improved by the addition of the toasted M. utilis seed meal. However, fish fed the diet containing 200 g kg?1 of raw M. utilis had poor growth with higher mortality (35%). Estimation of the feeding cost using the diets revealed reduction in production cost of fish with the inclusion of toasted M. utilis seed meal. It was concluded that toasting significantly improved the nutritional quality of this unconventional feedstuff, allowing better utilization at up to 200 g kg?1 inclusion level in the diet of African catfish C. gariepinus.  相似文献   

17.
Despite the large economic and social benefits fisheries can offer to address Africa’s development needs, investment in African fisheries and aquaculture has been remarkably low. However, if fisheries and aquaculture are to meet the challenges of technological change, institutional reforms and resource mobilization needed in support of the sector’s development potential, fisheries stakeholders must make the case for investment much more clearly within the context of wider socioeconomic development. In this paper, we argue that the global consensus around the Millennium Development Goals (MDGs) offers an important opportunity to pursue this agenda in Africa. In particular the MDGs’ human development focus provides a compelling framework for articulating the comprehensive value of fisheries for poverty reduction and long‐term socioeconomic development. The paper has two objectives. The first is to examine the direct and indirect links between fisheries and the individual MDGs, drawing together findings and lessons learnt from recent African case studies with relevant examples from elsewhere. The second is to translate these findings into recommendations for action in support of improved investments in fisheries aimed at increasing the overall development value of the sector.  相似文献   

18.
The effect of extenders was studied on the cryopreservation of sperm from African catfish, Clarias gariepinus (Burchell). The following six basic extenders were tested: fructose, glucose, sucrose, NaCl, KCl solutions and the artificial seminal plasma of the African catfish. Each of these extenders was tested both with and without buffer systems (i.e. NaHCO3-CO2 and Tris-HCl) by using 10% dimethyl-sulphoxide (DMSO) as a cryoprotectant. The two-step freezing was carried out in a programmable freezer by using the following freezing rates: (1) 4 °C min–1 between 3 and –4 °C; (2) and 11 °C min–1 between –4 and –80 °C. The best post-thaw motility (25%) was achieved with 333 mmol L–1 fructose solution and NaHCO3 buffer. The fertilization experiments were carried out with unbuffered fructose and glucose extenders using various amounts of sperm and two fertilization methods: (1) dry and (2) wet. The best fertilization rates were achieved with 75 μL of sperm and wet fertilization with glucose extender, or 100 μL of sperm and dry fertilization in case of fructose – both methods fertilized 96% of all eggs.  相似文献   

19.
Gastric evacuation rate, return of appetite and satiation time of African catfish, Clarias gariepinus Burchell 1822, fingerlings, fed with a commercial pelleted feed, were determined under experimental conditions. The gastric evacuation rate was described by an exponential function, which was found to be inversely related to the rate of ingestion (return of appetite). Satiation time remained constant over the experimental period. Based on these data the authors estimated maximum daily ration in relation to feeding schedule and feeding frequency for C. gariepinus fingerlings.  相似文献   

20.
The aim of this research is to evaluate the effects of biofloc system application at different fish density on the nursery production performance and the robustness of African catfish Clarias gariepinus (Burchell) against Aeromonas hydrophila and salinity stress. An economic analysis was also performed to determine the most optimum fish density in biofloc‐based African catfish nursery production. African catfish with an average body weight of 0.96 ± 0.04 g and average body length of 4.20 ± 0.46 cm, respectively, were distributed in 12 units of circular plastic‐lined tanks (1,020 L). The experiment consisted of four treatments in triplicates, that is, a control without carbon source addition at a density of 4 fish/L, and three biofloc treatments at different densities, that is, BFT4 (4 fish/L), BFT6 (6 fish/L) and BFT8 (8 fish/L). Tapioca flour was used as the organic carbon source in biofloc systems and was added at an estimated C/N ratio of 10. Housing the fish in biofloc systems resulted in higher fish growth, more efficient feed utilization, higher fish robustness against A. hydrophila infection and salinity stress, as well as higher profitability of nursery production. Increasing the fish density resulted in higher mortality. However, higher number of fish produced and lower feed conversion ratio were observed in the treatments with higher density (6 and 8 fish/L). In conclusion, the application of biofloc technology at a density of 8 fish/L could be recommended to increase the production and profitability of African catfish nursery culture.  相似文献   

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