Development,prospects and problems of the tilapia cage culture industry in The Philippines

The Philippines has vast freshwater resources for cage culture of fish. Two tilapia species, Tilapia mossambica and Tilapia nilotica, are cultured commercially in cages in several lakes.Field testing for cage culture of Tilapia nilotica, the preferred species, is described. A pilot commerical cage farm has been established.The major problems affecting development are the short supply of quality fingerlings, the lack of a standard commercial feed, and the increasing costs of cage construction. Recommendations for resolving these problems are given.     

Test of size-specific mass selection for Nile tilapia, Oreochromis niloticus L., cage farming in the Philippines

One generation of mass selection based on the collimation procedure (early culling of large fry) was applied on Nile tilapia, Oreochromis niloticus L., in net cages set in Laguna de Bay, Philippines. The objective was to test the effectiveness of a low-cost, small-scale broodstock improvement procedure in this culture environment. Directional selection was performed in two steps after initial removal of large fry at 21 days. Selection of parents and testing of the offspring were also conducted in hapa net cages set up in Laguna de Bay. The selection resulted in a significant positive response of 3% relative to the control, which represents a projected 34% gain over 5 years in Laguna cage culture. The realized heritability is ≈16%.     

Microcystin production during algal bloom occurrence in Laguna de Bay, the Philippines

ABSTRACT:   The amount of microcystin in Microcystis aeruginosa bloom was investigated during the rainy season of 1999 in Laguna de Bay, the Philippines. Bloom samples taken from the West Bay and East Cove stations of the lake were studied in relation to the characteristics of environmental conditions. Four types of microcystins, microcystin-LR (MC-LR), microcystin-RR (MC-RR), 6(Z)-Adda-microcystin-RR, and 3-desmethylmicrocystin-LR were identified from the natural bloom samples among which MC-LR was the most dominant type of microcystin. Production of microcystin (88.6 µg/100 mg dried cells) was highest during the first sampling week that coincided with high water transparency and high conductivity. The occurrence of a strong typhoon during the second sampling week had changed the environment drastically, which was characterized by low water transparency, high turbidity, low water temperature, and with trace amounts of MC-LR detected at the East Cove station. Thus, toxin production over time as well as the relationship between Microcystis production and toxin concentration could not be fully evaluated.     

巢湖设置网箱利用微囊藻类养殖罗非鱼、鲢、鳙试验

巢湖是安徽省第一大湖 ,正常面积 76 0 0 0公顷 ,历史上是我省的重要水产品生产基地。但近年来随着环境污染的日趋加剧 ,特别是沿湖大量营养盐的流入 ,加重了巢湖的富营养化 ,导致藻类大量繁殖 ,水华频繁出现 ,致使水产品产量年年下降 ,品种减少。治理巢湖 ,恢复资源 ,提高产量 ,是水产工作者的责任和沿湖群众的迫切要求。为探讨利用鲢、鳙、罗非鱼等滤食性鱼类摄食微囊藻 ,在增加水产品产量的同时 ,降低富营养化的可行性 ,我们于 2 0 0 0年在巢湖开展了设置网箱 ,养殖罗非鱼、鲢鱼和鳙鱼的试验 ,现将试验情况及我们的看法报告如下。1　材料…     

罗非鱼养殖技术之二池塘网箱套养罗非鱼技术

为充分挖掘池塘潜力,有效地利用水体空间,增产增效、节省饲料、降低饵料系数和有利于防病治病,笔者在中宁县农业局水产站基地面积为24.8亩的4口池塘中进行池塘网箱套养罗非鱼试验,取得了明显的经济效益和社会效益,现将池塘套放网箱养殖罗非鱼技术总结如下,以供广大养殖户参考试用。1.池塘选择:网箱放置在面积为6.3亩的池塘中,池塘水深1.8m~2.0m左右,水质较好,水源充足,进排水方便,并配备增氧机一台。2.网箱设置:用金属材料制成2.0m×2.0m×1.5m的柜子架,用聚乙烯塑料网衣将四周包围且最后留盖,网目为2.0cm~2.5cm,网箱放在靠近增氧机处,每口…     

中国渔村居民收入结构及其特征分析

改革开放以来,中国渔村居民收入演进经历了波动、反弹、减缓和低迷四个阶段。经过灰色关联分析得知,渔业收入依然是渔村居民收入的主要来源,同时,非渔业收入对渔村居民增收的推进作用在不断地提升。进而,指出现阶段渔村居民收入结构的地域性差异和收入来源多元化的特征。为"三渔"问题的解决、和谐社会的构建提供一些有益的借鉴。     

网箱养殖彩虹鲷的技术要点

彩虹鲷又称红罗非鱼、红吴郭鱼,系鲈形目,鲡鱼科,为尼罗罗非鱼和莫桑比克罗非鱼突变型的杂交良种,具有食性广、生长快、抗病力强、耐低氧等诸多优点.利用水库网箱养殖彩虹鲷,可以优化养殖结构,提高水体生产效率.通过近几年的养殖试验表明,要实现彩虹鲷水库网箱养殖高产高效,必须把握以下技术要点：     

罗非王网箱养殖高产试验

<正> 罗非王即台湾全雄性罗非鱼,是以奥利亚雄性原种与尼罗罗非鱼雌性原种交配而育成的三倍体。此鱼的雄性率高达 98％以上,因其生长速度快、肉质鲜美、内脏物少、效益高而在南方各省普遍推广。我市于2001年开始对此鱼进行试养,网箱单产达55.2kg/m~3,最大个体达1.4kg,平均个体达0.88kg,效益显著,现将试验情况报告如下。     

罗非鱼养殖技术之一宁夏地区池塘小网箱养殖罗非鱼

由于受自然环境限制，罗非鱼在银川地区只有每年５月２０日～１０月１０日期间可以在自然条件下正常生长，其余时间需在有保温、加温设施的环境中才能存活（银川地区尚无温泉渔场）。个体大于１５０g的罗非鱼背棘在活鱼运输中相互刺伤鱼体，形成病灶，使得罗非鱼长途运输中成活率低。本地区罗非鱼市场售价高，在养殖生产中，它是取得良好经济效益的养殖品种之一。三年来，笔者利用池塘设置小网箱养殖罗非鱼，充分利用水体空间，管理方便，尤其是可随时根据市场需要适量上市，并在不影响池塘中其他养殖品种生长的情况下，亩均增利１０００元…     

罗非鱼养殖技术之一豫东地区水库网箱养殖罗非鱼技术

虞城县石庄水库位于豫东平原的东部,是1953年利用黄河故道蓄水修筑的一座中型平原型水库,水库控制流域面积为825平方公里,正常蓄水水面面积为18600亩,现主要用于引黄补源蓄水和拦蓄雨水之用,无外来生活     

深水养殖网箱试验中网衣相似准则的应用

通过分析与试验相结合的方法对重力相似准则在网衣试验中的适用性进行研究。试验以在国内应用较广的田内相似准则作为参照,分析讨论了两种相似准则的异同,推导得出了重力相似准则结合大小尺度比在网衣模型设计中的质量校正公式及刚度校正公式。并据此按照两种相似准则,设计了包括网衣、底杆和沉子系统的两套模型,模型上端固定于设置了受力传感器的刚性直杆上。试验在纯流条件下进行,分别设置5组流速,试验水深0．8m。各组流速重复试验3次,受力由固定于刚性直杆上的传感器测量获得,网衣的变形则通过系缚在网衣上的二极管的坐标确定。在进行受力分析时,由于两相似准则的受力比尺不同,因此必须将模型受力按照对应比尺统一转换为原型值,同时利用受力与流速的回归关系式将模型受力校正为同一流速下的数值然后再进行比较。试验结果表明,相同流速条件下,两种相似准则的模型受力及变形总体上吻合较好,说明重力相似准则在网衣试验中采用质量校正及刚度修正后同样能够得到令人满意的结果,而且试验中模型的大尺度比达到1：20,这无疑为涉及波浪问题的深水网箱模型试验的设计提供了保障,从而避免了田内相似准则在深水网箱试验研究中应用的局限性。     

罗非鱼养殖技术之三小体积网箱高密度养殖罗非鱼技术

小体积网箱养殖罗非鱼,具有养殖密度大、管理方便、鱼体生长快、产量高、效益好等特点,是进行罗非鱼养殖的一种较好的方式。一、小体积网箱的结构小体积网箱一般由箱体、箱盖、饲料盘、投饲管、框架等几部分组成。网箱规格有1.0m×1.0m×1.1m、1.5m×1.5m×1.1m、2.0m×2.0m×1.1m等几种,箱体入水体积一般为1m3~4m3。网箱由聚乙烯网片缝合或由尼龙线编织而成,网目大小一般在2.0cm~2.5cm以上。箱盖由不透光的合成纤维布制成,其主要作用是阻止阳光直接进入网箱内,不使罗非鱼发现网箱上方有运动物,以及避免鸟类的袭击等,在实际生产中也有不用遮…     

A farmer-oriented Nile tilapia, Oreochromis niloticus L., breed improvement in the Philippines

Opportunities for developing small‐scale tilapia industry in the Philippines is hampered by the shortage of good‐quality seeds and broodstock. Most small‐scale farmers are dependent on distribution centres for improved tilapia seeds that are expensive and not sufficient to meet market demands. An option would be for farmers to develop their own tilapia breeds using simple procedures within their technical and financial resources. This option will also help sustain the diversity of locally adapted domestic stocks of tilapia. The Philippine tilapia production of ～122 316 MT can be increased by ensuring a stable supply of quality seeds and transferring suitable technology to fish farmers. The study was carried out in a tilapia hatchery/nursery pond in the Philippines to explore the potential for a farmer‐based research on tilapia breed improvement using relatively simple artificial selection procedures. One generation of size‐specific mass selection based on the early culling of large fry (collimation procedure) was applied on a Nile tilapia strain, Oreochromis niloticus L., in net cages set in a small earthen pond. Two episodes of directional selection were performed after initial removal of large fry at 21 days. Selection of parents and progeny testing were conducted in hapa and B‐net cages set in earthen ponds. The selection resulted in a significant response of 8% for standard length and 29% for weight relative to the control. The crude estimates of realized heritability is ～16% for standard length and ～26% for weight comparable with similar studies conducted by other workers.     

罗非鱼养殖技术之一水库网箱养殖彩虹鲷高产技术

彩虹鲷又叫红罗非鱼、红吴郭鱼,属鲈形目、罗非鱼属,是属内种间杂交培育出的优良养殖新品种,具有食性广、生长快、抗病力强、耐低溶解氧等特点,是市场上的畅销产品。为调整当地养殖品种,优化水产养殖结构,探索彩虹鲷养殖技术,2002年5月~10月,山东省平邑县水产局在大涝泉水库进行网箱养殖彩虹鲷高产试验,取得较好的经济效益和社会效益。一、水库条件大涝泉水库位于平邑县南部山区,面积450亩,水深7m~10m。选择在水库北部库湾处设置网箱,该处背风向阳,水面开阔,水位稳定,水质清新,水体溶解氧丰富,pH值7.2~8.0,水深4m~5m,且不易受洪水冲击。二…     

The economics of tilapia fingerling production and marketing in the Philippines*

Abstract. These analyses of the tilapia fingerling industry in the Philippines focus on the economics of production in different hatchery systems and on fingerling marketing channels. The analyses are based on cross-sectional data from government and private hatcheries in late 1982 and from December 1983 to March 1984. The relative profitabilities of different hatchery systems (land-based and lake-based) are estimated and economies of scale are analysed. Conceptual and methodological issues inherent in analyses based on cross-sectional data are discussed in the context of the extreme difficult standardizing inputs and output from private tilapia hatcheries which are characterized by wide variation in management practices.     

Periphyton fouling as a marginal energy source in tropical tilapia cage farming

In aquaculture, the benefit of autotrophic production within land-based ponds for fish production has long been recognized. In cage culture, organisms growing on the cage net have so far only been considered as a problem. This study investigated the potential production of periphyton on cage nets used in a tropical mixed tilapia culture of Oreochromis mortimeri (Trewavas), Tilapia rendalli (Boulenger) and Oreochromis niloticus (Linnaeus) in Lake Kariba, Zimbabwe. The production of periphyton was assessed experimentally and compared with the energy demand of the caged fish. The tilapias were found to graze intensively on the net, and the primary production of periphyton on the cage net was ≈ 1% relative to the energy demands of the fish.     

Bio-flocs technology application in over-wintering of tilapia

A 50-day experiment was conducted to investigate the effectiveness of the bio-flocs technology for maintaining good water quality in over-wintering ponds for tilapia hybrid fingerlings (Oreochromis niloticus × Oreochromis aureus). To preserve adequate water temperatures in the ponds, they were covered with polyethylene sheets and the water exchange rate was minimized to increase pond water temperature. To avoid water quality deterioration, starch was added to the ponds to stimulate the formation of bio-flocs. Temperature in the covered ponds could easily be controlled and was 0.4–4.9 °C higher than the influent water. Adjusting the C/N ratio in the ponds by adding starch or increasing the amount of carbohydrates added through the feed limited the presence of inorganic nitrogen species when the C/N was about 20, even at high stocking densities of 20 kg/m³ at harvest. Fish survival levels were excellent, being 97 ± 6% for 100 g fish and 80 ± 4% for 50 g fish. Moreover, at harvest the condition of the fish was good in all ponds with a fish condition factor of 2.1–2.3. Overall, these findings can help to overcome over-wintering problems, particularly mass mortality of fish due to low temperatures in the ponds.     

小尺度网箱缆绳张力在波浪中的变化特性

海水养殖网箱系统主要包括网箱框架、网衣和锚泊系统.其中锚泊系统是网箱系统安全的重要保证之一,而锚泊系统设计的核心问题是系泊力,即缆绳张力问题.为了保证受风浪冲击的网箱锚泊安全,必须对锚泊的动力负荷进行分析研究.为此本研究设计了一种小尺度网箱进行试验,通过测量不同波长、波高的波浪中网箱的缆绳张力、以及波浪通过网箱前后时的平均波高及波长,对网箱缆绳张力随波长、波高的变化进行分析和研究.结果表明,波浪中缆绳张力最大张力随波高的增加而增加,且随着波浪周期的增加张力增加的趋势随波高变缓,而波浪的波长和网箱框架的边长一致时,波浪单位截面积内的能量损失率达到最大值.     

Effect of stocking density on the growth performance and yield of Nile tilapia [Oreochromis niloticus (L., 1758)] in a cage culture system in Lake Kuriftu,Ethiopia

This research was conducted to investigate the effect of stocking density on the growth performance and yield of Oreochromis niloticus in cage culture in Lake Kuriftu. The treatments had stocking densities of 50 (50F), 100 (100F), 150 (150F), and 200 (200F) fish per m^?3. All treatments were in duplicate. Juveniles with an average weight of 45. 76±0.25 g were stocked in the treatments. The fish were fed a composite mixture of mill sweeping, cotton seed, and Bora food complex at 2% of their body weight twice per day using feeding trays for 150 days in powdered form. The growth performance of O. niloticus was density dependent. The final mean weight of O. niloticus ranged 147.76±0.28–219.71±1.42 g and the mean daily weight gain was 0.69±0.01–1.15±0.02 g day^?1. Fish held in cages with lower density were heavier than the ones held at higher densities, and showed higher weight gain and daily weight gain. The most effective stocking density, in terms of growth parameters, was 50 fish m^?3. The gross yield (4.5–20.55 kg cage^?1) showed a significant difference with increasing stocking density (P<0.05). Moreover, the apparent food conversion ratio (2.48–7.22) was significantly affected by stocking density (P<0.05). However, survival rate was not affected by stocking density (P>0.05). It can be concluded that the most effective stocking densities were at 50 fish m^?3 cage for larger size fish demand in a short period and 200 fish m^?3 for higher gross production with supplementary feed.     

Factors affecting the fishing power of sardine fishing vessels and implications for the management of the fisheries on Lake Kariba, Zimbabwe

Abstract The factors important in determining fishing power in the Lake Kariba sardine, Limnothrissa miodon (Boulenger, 1906), fishery were identified using data from the major fishing area of the lake, the Kariba basin, for the periods 1980–1982 and 1988–1990. Comparisons were carried out using fishing power calculated from the mean catch of some standard vessels. Three methods were used for identification of the important attributes. Analysis of variance (ANOVA) was carried out for each component to compare the mean fishing power at all levels within each variable. Multiple regression analysis was used to build predictive models and to determine the factors which best predict fishing power. Factor analysis was used to ordinate vessel types and examine any vessel groupings related to fishing power. Factor analysis showed that vessel and net size were the most important variables. Vessels without engines for propulsion, of low value and without radios had less fishing power than the other vessels in the fleet. Vessels from the same company had similar fishing power, suggesting that some unmeasured variable such as quality of management linked to the fishing companies had a significant effect on catch. The factors which were important in determining catch were length of vessel, depth of the net, presence and absence of echo sounder, mobility, the type of light, number and wattage of the underwater lights in the 1988–1990 fishing period. Vessel length and net category were most important in the period 1980–1982. The models accounted for between 37.6 (1981) and 61.2% (1988) of the variation in fishing power. During the development of the fishery, there has been a change from purse seine to lift nets, and increases in the use of echo sounders, engines for the propulsion of vessels and radios, all of which could have increased effective fishing effort.