Strategies for further development of aquatic feeds

ABSTRACT: To date, aquatic feeds have depended heavily on fishmeal and fish oil as their source of protein and lipid. However, the feed industry is encountering shortfalls in the availability of these ingredients because of a decline in the number of fish captured in the wild and the increased human demand for some of the species currently being used for fishmeal and oil production. Therefore, efforts are now being directed in different parts of the world to finding alternative quality ingredients, which ideally are less expensive and readily available for use in practical diets. The data accrued have shown that a large proportion of both fishmeal and fish oil can be replaced by other protein and lipid sources. However, it is emphasized that an optimal essential amino acid balance be maintained and that the n-3 highly unsaturated fatty acid requirement be satisfied when combining economical protein and lipid ingredients. Newly developed feeds should aim at being nutrient-dense in order to reduce the output of solid, P and N waste. This can be done through improving nutrient availability, optimizing the digestible protein to energy balance of the diet, and replacing dietary fishmeal with alternate ingredients. These diets should also be effective for maintaining good health and improving disease resistance in fish through enhancement of immune responses. A wholesome approach to culturing fish would be to use appropriate feeding standards that are aimed not only at improving economic returns but also at developing a lasting cohabitation of sustainable aquaculture and a cleaner environment. Furthermore, in the 2lst century aquaculture would still retain its place as a prominent source of food protein, signifying that fish feed research remains a forceful area in discovering better feeds for the industry.     

Substituting fish meal with soybean meal in diets of juvenile cobia Rachycentron canadum

An 8-week feeding trial was conducted with cobia to determine the amount of soybean meal that could replace fish meal in formulated diets without reducing growth. Juvenile cobia (initial mean weight, 32 g) were fed 48% crude protein diets in which dietary protein was supplied by brown fish meal or a mixture of hexane extracted soybean meal and the fish meal, resulting in 10%, 20%, 30%, 40%, 50% and 60% of fish meal protein being replaced by soybean protein. The fish readily accepted all seven experimental diets and no fish died during the trial. Detrimental effects on growth performance were obvious when half of the fish meal protein was replaced by soybean protein. There existed a significant difference in fish weight gain, feed conversion ratio (FCR), protein efficiency ratio (PER) and net protein utilization (NPU) when the replacement level for fish meal protein was increased from 40% to 50%, indicating that up to 40% of fish meal protein can be replaced by soybean meal protein without causing reduction in growth and protein utilization. On the other hand, quadratic regression analysis shows a growth optimum at 16.9% replacement of fish meal protein by soybean meal protein. Lipid concentrations in the cobia muscle increased significantly as dietary soybean meal increased. Muscle concentrations of free threonine and histidine decreased as use of the soybean meal increased in the diets. Since methionine concentration in the test diets decreased from 2.52 to 1.36 g 16 g⁻¹ N as the soybean meal protein replacement level was increased from 0% to 60% while all other essential amino acids remained relatively constant, dietary requirement of methionine was calculated assuming it was equally available between the two proteins. The broken-line model analysis based on fish weight gain shows a breakpoint when dietary methionine+cystine concentration was 2.66 g 16 g⁻¹ N or 1.28 g 100 g⁻¹ diet.     

鱼蛋白的综合利用途径1.鱼粉

就有关低值鱼及水产加工废弃物中鱼蛋白的开发研究及应用情况做系列介绍,本文就低值鱼蛋白主要利用形式即鱼粉进行了分析和讨论。     

Studies on the utilization by rainbow trout (Salmo gairdneri Rich.) of feed mixtures containing soya bean meal and an addition of amino acids

This paper deals with the growth of fish and utilization of feed mixtures in which fish meal is partly substituted by powdered soya beans. In order to improve the quality of protein in the feeds, they were enriched with synthetic amino acids. The food coefficients of the feeds were calculated, as were the protein efficiency ratio and apparent net protein utilization, by chemical analysis.

The results of the experiment showed that an addition of amino acids improved the utilization of feeds. It was found that rainbow trout can utilize soya bean protein enriched with cystine (1%) and tryptophan (0.5%) almost as well as protein from the fish meal.

Chemical composition of the experimental fish is discussed, as well as the amino acid composition of fish muscles and selected physiological parameters: haematocrit, haemoglobin content in the fish blood, the hepasomato index, and the content of protein, amino-transferases and cholesterol in the fish blood serum.     

FISH CONSUMPTION AND FOOD SECURITY: A DISAGGREGATED ANALYSIS BY TYPES OF FISH AND CLASSES OF CONSUMERS IN SELECTED ASIAN COUNTRIES

ABSTRACT

This paper discusses fish consumption and preference patterns for fish species by income groups, and by urban/rural divide in Bangladesh, China, India, Indonesia, the Philippines, Thailand, and Vietnam. The analysis is based on primary data collected by the WorldFish Center and its partner institutes by means of a survey of 5,931 households in the selected countries. The FAO database and other published materials were also used to analyze trends in fish consumption. Freshwater fish species constitute a major share in total per capita fish consumption in most of these countries. Pelagic and demersal marine fish are the main contributor to per capita total fish consumption in the countries with longer coastal boundaries (such as Indonesia, the Philippines and Thailand), and in the coastal regions within each country. Results suggest that fish contributes between 15% and 53% of the total animal protein intake in these countries. Fish consumption varies widely with economic position of the households, in terms of both per capita consumption and type of fish species. Per capita fish consumption increases with increase in income. The share of fish protein in total animal protein expenditure is higher for lower income groups, demonstrating their dependence on fish as a source of animal protein. Poor people consume mostly low-price fish and rich people spend a significant portion of their fish budget on expensive fish. Per capita fish consumption is substantially higher in rural areas than in urban areas.     

水解鱼蛋白的营养特征及其在水产动物营养饲料中的研究进展

鱼粉短缺是当今水产饲料行业中亟待解决的难题,而水产品加工副产品占水产品的总重量超过60%,因此,充分利用水产品加工副产品,提高其营养价值,是解决鱼粉短缺的重要途径。水解鱼蛋白是水解水产品加工副产品而得到的富含游离氨基酸和不同肽链长度的蛋白寡肽,目前,越来越多的研究证明,其对水产养殖动物的生长性能具有重要的促进作用。本文从水解鱼蛋白的制备、营养特性及水产饲料中的研究和应用方面展开综述,系统论述近年来水解鱼蛋白在水产动物营养相关领域的研究成果,并提出在水产饲料中的进一步研究方向,以期为水解鱼蛋白在水产动物营养学研究及其在水产饲料中的应用提供参考。     

Comparison of Practical Diets with and without Animal Protein at Various Concentrations of Dietary Protein on Performance of Channel Catfish Ictalurus punctatus Raised in Earthen Ponds1

Abstract— A 2 × 5 factorial experiment was conducted using practical-type extruded feeds containing 20, 24, 28, 32, or 36% crude protein with or without animal protein. The animal protein supplement consisted of 4% menhaden fish meal and 4% meat, bone and blood meal. Channel catfish fingerlings (average size: 26.3 g/fish) were stocked into 50 0.04-ha ponds at a rate of 24,700 fishha. Five ponds were used for each dietary treatment. Fish were fed once daily to satiation for 202 d. There were no differences in feed conversion ratio (FCR), percentage fillet moisture, and survival among treatments. In fish fed diets containing no animal protein, feed consumption, weight gain, and percentage dressout were lower for fish fed the 20% protein diet than those fed diets containing 28% and 32% protein. Fish fed 28, 32, or 36% protein diets without animal protein did not differ in respect to percentage dressout and percentage visceral fat; fish fed the 36% protein diet had higher percentage fillet protein and a lower percentage fillet fat than fish fed other diets with the exception of fish fed the 28% protein diet. In fish fed diets containing animal protein, feed consumption, weight gain, percentage fillet protein and ash, and percentage dressout were lower and visceral fat was higher for fish fed the 20% protein diet than those fed other diets. Fish fed diets containing 24% protein and above with animal protein were not different in respect to weight gain and feed consumption, but fish fed the 24% protein diet had a higher percentage fillet fat than fish fed a 32% or 36% protein diet. Fish fed the 32% protein diet had a lower visceral fat. Considering animal protein vs non-animal protein with the data pooled across all diets without regard to dietary protein level, weight gain and FCR of fish fed diets containing animal protein were higher than those fed diets containing no animal protein. However, weight gain of fish fed diets containing 20, 28, or 32% protein with or without animal protein did not differ. Dressout percentage and fillet protein were higher and fillet fat was lower for fish fed diets containing no animal protein than those fed diets containing animal protein. Data from this study indicated that animal protein may not be a necessary dietary ingredient for fish fed 28% or 32% protein diets typically used for grow out of pond-raised channel catfish under satiation feeding conditions. Whether animal protein should be included in catfish diets containing less than 28% protein is unclear, since fish fed the 24% protein diet benefited from animal protein but those fed the 20% protein diet did not benefit from animal protein. Additional studies to provide more information on low-protein, all-plant diets are currently being conducted.     

鱼粉在水产饲料中的应用研究

As a main protein source in aquafeeds, fish meal has been extensively studied. Fish sources, freshness, processing temperature, lipid quality and microbiological index are five main aspects of the evaluation of fish meal quality. This paper reviewed the researches on fish meal including the evaluation of fish meal quality, the use of fishmeal and the environmental problems. Biogenic amine is the main potential toxin in decomposed fish meal including mainly histamine, cadaverine, putrescine and tyramine and most studies showed that they could affect the fish growth performance and health. The determination of protein digestibility of fish meal includes pepsin-digestion method, animal test, capillary electrophoresis, etc. The content of phosphorus in fish meal and its utilization can introduce pollution to water bodies and the use of alternative protein and improvement of utilization of fish meal can help to reduce the pollution from fish meal.     

Effects of Dietary Protein Levels on Gonad Maturation, Size and Age at First Maturity, Fecundity and Growth of Nile Tilapia

Six-week-old Nile tilapia (Oreochromis niloticus) fry with an average weight (SD) of 0.51(0.2) g were reared for 140 days on five formulated, isocaloric diets of different protein levels (25, 30, 40 and 45% by dry weight). Fish fed diets of higher protein levels (40 and 45%) showed better growth and feed conversion ratio than those on lower protein levels. Fast-growing fish matured earlier. Maturation rate was affected by the dietary protein levels. Males matured earlier than females: the first mature males were recorded when they were 14 weeks old, whereas the females matured after 18 weeks. In both sexes, mean percentage of mature fish rose with increasing dietary protein level, the percentage of mature males being higher than that of the females. Similarly, the percentage of mature fish rose with the increasing age of fish, with more than 50% males and females mature at the age of 22 and 24 weeks, respectively, the exception being the 25% protein diet fed fish, where the percentage of mature fish was below 50%. In all treatments, spawning was initiated when the fish were 22 weeks old. Smallest size at spawning of males and females was 9.2 cm (13.1 g) and 8.1 cm (8.9 g), respectively, and dietary protein levels influenced the size of fish at first maturity. For both sexes, no difference was found in the gonado-somatic index (GSI) among different treatments. Fecundity increased with increasing dietary protein levels, but significant differences were found only between 40–45% and 25–35% dietary protein levels. The relative fecundity (eggs g^–1 female) was higher at the lower dietary protein levels (25–35%) than at the higher dietary protein levels (40–45%). The dietary protein levels did not have any significant influence on the size and weight of mature eggs. The chemical composition of fish and mature ovaries was significantly influenced by the dietary protein level.     

Gene Knockdown: A Powerful Tool for Gene Function Study in Fish

So far, there are a number of fish genome projects, including experimental and economically important fish that provide available DNA sequence information. However, the function of a gene cannot be deduced only by its DNA sequence. Therefore, a technique with which to investigate the function of the fish gene is needed. Gene knockdown (GKD), or antisense technology, is now being used as a powerful technique to study gene functions in living organisms. GKD effects result from the introduction of an antisense molecule into living cells. The antisense agents bind to target messenger RNA, thus inactivating the target gene expression. The appropriately spatial inhibitory effects on protein production from corresponding gene resulted in the phenotypic change. Therefore, the function of the gene can be understood. To date, there are a number of antisense molecules that can affect efficient GKD in fish. These include antisense oligonucleotides, small interfering RNA, and ribozyme. These antisense molecules cause specific gene inhibitor effects with different mechanisms. The various antisense mechanism types facilitate a number of GKD applications with various approaches in animals. In this review, we demonstrate the characteristics of each antisense molecule, its mechanism, and its application, especially for gene functional analysis in fish.     

高不饱和脂肪酸（HUFAs）在淡水鱼类中的营养作用研究进展

鱼粉、鱼油资源的短缺促使全球水产养殖业积极寻找其替代原料,而探究鱼粉、鱼油与其替代物之间的差异尤为重要,其中最主要的差异就是高不饱和脂肪酸(highly unsaturated fatty acids,HUFAs)是否存在及其含量多少。HUFAs是一类碳原子数目≥20、双键数≥3的脂肪酸,具有为动物提供能量、构成细胞膜组分、形成高生物活性物质、调控脂质代谢和免疫功能等重要作用,主要存在于鱼油和某些类别的微藻中。淡水鱼类具备自身合成HUFAs的能力,因此,一般认为HUFAs不是淡水鱼类的必需脂肪酸,无需通过饲料提供。但已有研究指出,饲料中添加一定量的HUFAs能够对淡水鱼类产生积极的营养作用,表明淡水鱼类的脂肪酸营养理论尚需进一步完善。本文综述了HUFAs在淡水鱼类生长、脂质代谢、健康免疫、繁殖特性等方面发挥作用的相关研究结果,明确提出淡水鱼类需要摄取一定水平的外源性HUFAs,指出在当前淡水鱼饲料中普遍使用HUFAs相对缺乏的蛋白源和油脂源的背景之下,HUFAs对淡水鱼类的作用应受到关注。最后,本文对今后淡水鱼类HUFAs营养的研究方向,以及新的HUFAs油脂源的开发前景进行了展望。     

The development of a remotely operated vehicle (ROV) for aquaculture

A prototype remotely operated vehicle (ROV) is being developed for use in aquaculture. The initial task for which the ROV has been built is to carry video cameras to provide pictures of fish for automatic image analysis. This paper explains the constraints on the design of the ROV, arising from hydrodynamic and practical considerations, and how these have been accommodated. The results of tank tests and field trials are reported.     

Effects of fish stocking and fishing pressure on fish community structures in French lakes

Fish stocking and regulation of fishing activities are widely implemented by freshwater fisheries authorities who have to protect aquatic communities. The effects of fish management on fish communities have not received sufficient attention. As a result of two datasets, one from EU Water Framework Directive (WFD) monitoring surveys, and one from a French survey targeting angler's associations, this study investigated the impacts of both fishing intensity and fish stocking on fish communities in French lakes. Both co-inertia analysis and community size spectra analysis, showed that: (i) stocking does not contribute to the standing stocks for five of the six most stocked fish species in France; and (ii) neither fishing intensity nor fish stocking lead to a change in the proportion of large and small fish. The results support alternative methods being promoted to enhance native fish populations.     

动植物蛋白源替代鱼粉研究进展

With the fast development of aquaculture, fish meal needs increased in recent years, however the quantity of fish catching decreases gradually. Fishmeal is a limited feed resource, and serious concem exists on the future availability of this feedstuff for incorporation in fish diets. Undoubtedly, fish meal is well recognized as the best dietary protein source for most marine carnivorous fishes which required high dietary protein levels compared to omnivorous or herbivorous fish. Fishmeal is known for their high content of essential amino acids and fatty acids, low carbohydrates, high digestibility, low levels of anti-nutritional factors (for fresh fish meal) and is a very good source of minerals and is highly palatable. Thus fish meal is in high demand as the protein source for many formulated diets. However, production of fish meal consumes approximately 35 % of the total global fish catch, and the increasing price and potentially unstable supply in the market could be limiting factors for marine fish culture. There have been strong efforts to define and develop cost-effective protein sources that can, at least partly, substitute for expensive high-quality fish meals in least-cost feed formulations. The search for fish meal substitutes and altemative dietary protein sources is an international research priority that could be of considerable economic advantages. Therefore it is urgent task to find animal and plant protein sources in place of fish meal. Among these, plant feedstuffs have received most attention in recent years, but due to their amino acid unbalances, .presence of anti-nutritional factors and low palatability, a high level of replacement of fish meal with plant feedstuffs in omnivorous fish is generally not well accepted. This paper reviews the research status for other protein sources replacing fish meal based on available information in the literature. Animal and plant protein sources nutrient values are evaluated from the aspect of digestibility, antinutrients, physiological status and suitable supplementation.     

Evaluation of Three Strains of Channel Catfish Ictalurus punctatus Fed Diets Containing Three Concentrations of Protein and Digestible Energy1

Abstract A 3 × 3 factorial experiment was conducted using three strains of channel catfish Ictalurus punctatus, USDA102, USDA103, and Mississippi normal (MN), and three concentrations of dietary protein. Three practical diets were formulated to contain 25, 35, or 45% crude protein with digestible energy/protein ratio of 10.0, 8.1, or 6.8 Kcal/g, respectively. Juvenile channel catfish (mean initial weight: 15.1 g/fish) were fed the experimental diets twice daily to approximate satiation for 8 wk. Regardless of dietary protein concentration, the USDA 103 strain consumed more feed, gained more weight, and converted feed more efficiently than other two strains. The MN strain consumed less feed and gained less weight than the other strains. Regardless of the strain of channel catfish, differences in weight gain, feed consumption, and feed conversion ratio were observed among fish fed diets containing various levels of protein with the 35% protein diet being the best. Neither dietary protein concentration nor strain had significant effect on fillet protein level. Data pooled by fish strain showed that fish of MN strain had lower fillet fat and higher moisture than fish of other two strains. Data pooled by dietary protein showed that fish fed the 45% protein diet had a lower level of fillet fat than fish fed the 35% protein diet, but this did not appear to be a strain effect, rather it was a result of decreased feed consumption. Results from this study clearly demonstrate that per formance of the USDA103 strain of channel catfish was superior to other strains tested. The growth characteristics of the USDA103 strain of channel catfish make the strain a promising candidate for commercialization. However, data are needed on performance of the strain from fingerling to marketable size under conditions similar to those used for the commercial culture of channel catfish prior to their release to the catfish industry.     

The use of immunostimulating herbs in fish. An overview of research

The use of immunostimulants as an alternative to the drugs, chemicals and antibiotics currently being used to control fish diseases in fish culture is attracting the attention of many researchers. In this context, many have focused on the use of medicinal plant products as potential therapeutic measures for modulating the immune response and, specifically, on the use of herbs to prevent and control fish diseases. Medicinal plants (plant remedies) are a deeply rooted component of the cultural heritage of many people from diverse cultures and countries and are, as such, closely linked to the maintenance of good health. The aim of this paper is to review research currently being carried out on the herbs and herbal extracts that have been shown to modulate the immune system of fish. Special attention is given to the use of Chinese and Indian herbs.     

The use of fish meal and soyabean meal as a protein source in the diet of grass carp fry

Diets based on fish meal and soyabean meal were fed to grass carp fry, the average body weight of each individual being 0.4 g. During the 70 days of the experiment, the best results were obtained with a diet containing 40% fish meal, when growth increment, protein efficiency ratio and apparent net protein utilization amounted to 209, 1.26 and 20.3, respectively. There was a deficiency in sulphuric amino acids in both fish meal- and soyabean meal-containing diets, and this was particularly marked in the latter. A significant decrease in available lysine was found in the diets containing soyabean meal. The main reason for the retardation in fish growth and the reduction of protein utilization when soyabean meal content is increased in the diets, seemed to be that the destruction of anti-nutritional factors by the heat processing of the meal was only partial.     

饲料中脂肪与蛋白质比对大口黑鲈生长、体组成和非特异性免疫的影响

为探讨大口黑鲈饲料中不同脂肪与蛋白质含量比对其生长、体组成和非特异性免疫的影响,实验设计了8种(D1~D8)不同脂肪与蛋白质含量比的总能递增饲料。D1~D8饲料的脂肪水平递增(9.0%～26.5%),而蛋白质水平递减(52.0%～31.0%)。用上述饲料饲养体质量为(10.06±0.02)g的大口黑鲈88 d,每饲料设3重复,每重复30尾鱼。结果显示,特定生长率、饲料效率、蛋白质消化率、脂肪消化率和脂肪沉积率均以D2组最高,但随饲料中脂肪与蛋白质含量比的进一步升高呈现显著下降趋势。D3~D5组的蛋白质效率显著高于D1和D8组。D2、D3组与D4组间的蛋白质沉积率差异不显著,但显著高于其他各组。D1~D4组间的总能消化率差异不显著,但显著地高于其他各组。饲料中脂肪含量过高对鱼体组成产生显著的影响,使体脂的积蓄显著增高。随着饲料中脂肪与蛋白质含量比的升高,成活率呈显著下降趋势,D1和D2组的成活率显著高于D5~D8组。非特异性免疫分析显示,D4组血清溶菌酶活力和D2组血清补体活性及头肾白细胞呼吸爆发活性为最高。以饲料为单因子作单因素方差分析得出,满足大口黑鲈最适生长和饲料利用的饲料蛋白质和脂肪水平分别为49.30%和11.50%。以饲料中蛋白质和脂肪水平为自变量,分别以特定生长率和蛋白质沉积率为因变量进行二元二次回归分析得出,特定生长率最大时,饲料中蛋白质、脂肪和脂肪与蛋白质含量比分别为48.20%、12.44%和0.26;蛋白质沉积率最高时,饲料中蛋白质、脂肪和脂肪与蛋白质含量比分别为46.42%、13.96%和0.30。以饲料蛋能比为自变量作一元二次回归分析得出,蛋白质沉积率最大时,饲料的蛋能比、蛋白质、脂肪和脂肪与蛋白质含量比分别为23.72mg/kJ、46.16%、14.18%和0.31。研究认为,饲料的脂肪和蛋白质水平对大口黑鲈的生长、体组成、饲料效率和免疫力有着不同程度的影响;饲料中过高的脂肪会抑制蛋白质的消化与利用,表明脂肪对蛋白质的节约作用有限。建议大口黑鲈实用饲料的蛋白质和脂肪水平分别保持在46%~49%和11.5%~14%范围内较为适当。     

Psychophysics and the Sensory Assessment of Fish

Procedures for sensory evaluation of fish often give the appearance of being empirical, that is, having been developed from practice without any contribution of underlying theory. The fundamental principles of sensory evaluation lie in psychophysics, a branch of psychology. Some textbooks of sensory evaluation have sections on psychophysics, but they are based on what might be called classical psychophysics which is summarized by the Weber/Fechner laws. Contemporary psychophysics has theories and practices which have wider applications in sensory evaluation of foods than classical psychophysics and can be applied to the advantage in the sensory analysis of fish. Three examples from the author's own experience will be presented in this discussion paper: use of the Theory of Signal Detection in evaluating taints; use of similarity ranking methods and multidimensional scaling for grouping fish by sensory properties; and application of current ideas of scaling to the measurement of freshness.     

Examination of net volume reduction of gravity-type open-net fish cages under sea currents

Owing to heavy criticisms of nearshore fish farming for causing environmental pollution and encroaching on sea space used for shipping, boating, recreational sea activities and marine eco-tourism, offshore fish farming has now being seriously considered. Moreover an offshore site provides more pristine water and greater space for increased fish production. However, offshore fish farming poses challenges such as a more energetic sea environment. A higher sea current can lead to large deformation of fish net and hence a net volume reduction which compromises fish welfare. With the view to identifying the effects of various important parameters on net volume reduction of a gravity-type open-net fish cage, this paper adopts a mass-spring model for the dynamic analysis of current-induced net deformations of cylindrical fish nets with discrete weights hanging at the bottom edge of the nets. In this model, the net mesh comprises knot nodes and bar nodes connected by tension-only massless springs. The spring stiffness is determined from the net bar diameters and material properties. The current-induced loads are applied to each node and calculated based on Morrison’s equation. The governing equation system for nodal motions can be established according to Newton’s second law, and solved by using the Runge-Kutta method for the real-time net deformations. The effects of net string reinforcements, weight distributions and net shapes on the net volume reduction are studied with the view to shed insights into how one may improve fish cage designs to effectively mitigate net deformation under high sea current speeds in offshore fish farming sites.