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Age, growth and mortality characteristics of the Thumbprint Emperor (Lethrinus harak) in Zanzibar 桑给巴尔拇指皇帝(Lethrinus harak)的年龄、生长和死亡率特征
Pub Date : 2024-03-12 DOI: 10.4314/wiojms.v23i1.2
T. A. Mussa, Saleh A.S Yahya, Jose J Castro, L. Chauka
The growth parameters of Lethrinus harak were studied in Zanzibar water from 308 samples collected between June 2019 to May 2020 at Unguja Ukuu and Mkokotoni landing sites. The annulus count indicated that the majority of fishes captured were of three and four years old and very few were five, six, and seven years of age with a mean length of 17.69 cm, 21.04 cm, 24.18 cm, 25.86 cm, and 28.15, respectively. The number of rings was counted on the whole otolith and the growth rings were revealed to be formed annually, with the opaque margins generated from December to February and the hyaline ones during the rest of the year. The growth parameters were estimated as L∞=34.22cm, K=0.25 year-1, and t0=0.00. The total mortality (Z) was estimated as 0.68 year-1 and natural mortality (M) was estimated using Pauly's equation, as 0.65 per year-1 and fishing mortality (F) was 0.03 year-1, which gives an exploitation rate (E) of 0.04 year-1. Although these values indicate the species to be underexploited, the absence of older individuals 15 years and smaller below three years might have affected our findings.
对2019年6月至2020年5月期间在温古贾乌库和姆科科托尼登陆点采集的308份桑给巴尔水样中的Lethrinus harak生长参数进行了研究。环数计数表明,捕获的大多数鱼类年龄为三岁和四岁,极少数为五岁、六岁和七岁,平均体长分别为 17.69 厘米、21.04 厘米、24.18 厘米、25.86 厘米和 28.15 厘米。对整个耳石上的年轮数量进行了统计,结果表明生长年轮每年形成一次,不透明的年轮产生于 12 月至次年 2 月,其余时间则为透明年轮。生长参数估计为:L∞=34.22厘米,K=0.25年-1,t0=0.00。总死亡率(Z)估计为 0.68 年-1,自然死亡率(M)根据保利方程估计为 0.65 年-1,捕捞死亡率(F)为 0.03 年-1,因此开发率(E)为 0.04 年-1。尽管这些数值表明该鱼种的开发程度较低,但 15 年以上的大个体和 3 年以下的小个体的缺失可能会影响我们的研究结果。
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引用次数: 0
Salinity tolerance of Nile tilapia (Oreochromis niloticus) to seawater and growth responses to different feeds and culture systems 尼罗罗非鱼(Oreochromis niloticus)对海水的耐盐性以及对不同饲料和养殖系统的生长反应
Pub Date : 2023-11-28 DOI: 10.4314/wiojms.v22i2.6
D. Mirera, Douglas Okemwa
The inability to acclimatise, feed and grow Nile tilapia (Oreochromis niloticus) in full seawater salinity has been a major obstacle to farming in marine waters. We investigated the salinity tolerance of O. niloticus and growth responses to different feeds and culture systems. Fish were first acclimatised to different salinities in laboratory aquaria, and the survival and growth performance in sea water were then assessed in aquaria, cages and ponds. Acclimatization to seawater salinity (5 – 30) took place at a rate of 5 every 9 days. Fish were stocked at densities of 5 fish/20 L in aquaria, 5 fish/m2 in cages and 3 fish/m2 in ponds. Replicates of 5, 3 and 3 were performed in aquaria, cages and ponds, respectively. Fish were fed on commercial (1 and 2) and locally formulated (30 % crude protein) diets. Mortality rates were higher in aquaria, when fish were introduced to salinities between 5 and 30 over 24 hours. Gradual salinity adjustments attained a stable survival rate of 78 % at salinities above 30. Aquarium experiments indicated significant negative correlation between salinity and survival (p < 0.001, r = 0.387) and daily growth rates varied with diet (0.01 – 0.05 g/day). Acclimatized fish showed minimal mortality in ponds and cages. Daily growth rates varied with diet and culture system; 0.54 - 2.48 g/day in cages and 1.1 - 2.5 g/day in ponds. Fish fed on commercial feed 2 showed significant growth rates for all culture methods (p < 0.05). O. niloticus could be fully acclimatised to seawater and attained promising growth rates when subjected to different commercial diets indicating potential of farming the species in marine waters.
尼罗罗非鱼(Oreochromis niloticus)无法在全海水盐度环境中适应、喂养和生长,这一直是在海水中养殖的主要障碍。我们研究了尼罗罗非鱼的耐盐性以及对不同饲料和养殖系统的生长反应。首先在实验室水族箱中让鱼适应不同的盐度,然后在水族箱、网箱和池塘中评估鱼在海水中的存活率和生长表现。海水盐度(5 - 30)的适应过程每 9 天进行 5 次。鱼的放养密度为:水族箱 5 条/20 升,网箱 5 条/平方米,池塘 3 条/平方米。在水族箱、网箱和池塘中分别重复 5、3 和 3 次。鱼的饲料分别为商品饲料(1 和 2)和当地配制的饲料(30% 粗蛋白)。在水族箱中,当鱼在 24 小时内摄入 5 至 30 度的盐度时,死亡率较高。逐步调整盐度后,当盐度超过 30 时,存活率稳定在 78%。水族箱实验表明,盐度与存活率之间存在明显的负相关(p < 0.001,r = 0.387),日生长率随日粮而变(0.01 - 0.05 克/天)。适应性鱼类在池塘和网箱中的死亡率极低。日生长率因饲料和养殖系统而异:网箱为 0.54 - 2.48 克/天,池塘为 1.1 - 2.5 克/天。投喂商品饲料 2 的鱼类在所有养殖方法中都有显著的生长率(p < 0.05)。尼罗河鱼类可以完全适应海水,并在摄入不同的商业饲料后获得了良好的生长率,这表明该鱼种具有在海水中养殖的潜力。
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引用次数: 0
Diet and trophic interactions between catadromous eels and sympatric fish in Kenyan east flowing river systems 肯尼亚东流河系溯河鳗鱼与同域鱼类之间的饮食和营养相互作用
Pub Date : 2023-11-28 DOI: 10.4314/wiojms.v22i2.7
Japhet K. Tembo, C. Kihia, Nzula Kitaka, Gordon C. O'Brien, Céline Hanzen, E. Mbaru, Kariuki C. Wanjiru
Biotic interactions such as competition and predation are important ecological drivers of population structure. Interactions among higher trophic level fish can contribute to further population declines in species, such as eels, made vulnerable by overexploitation or environmental change. Furthermore, trophic interactions may further predispose eel populations to collapse, but this is poorly understood, particularly along the Western Indian Ocean (WIO) rivers. This study evaluated stomach contents of fish captured with glass and commercial fyke nets in the Athi and Ramisi Rivers, which discharge into the WIO. Stomach contents were examined using dissecting microscope to establish diet composition. Eels primarily consumed assorted fish (43 %), and crustaceans (36 %); such as penaeid shrimp (14%) and prawns (13%) and crab (9%), thus belonged to a higher trophic level (TL) of 3.47 than native (2.98) or introduced (2.8) sympatric fish species. Diet breadth of eels was significantly lower (0.20) than for sympatric fish species (0.27), attributed to higher diet specialization. The TL of carnivorous fish (3.19) and their diet compared well with those of eels, even though diet preference differed significantly among fish types. Consequently, eels ranked as vulnerable by the IUCN are further threatened by previously undescribed competition from carnivorous fish.
竞争和捕食等生物相互作用是种群结构的重要生态驱动因素。高营养级鱼类之间的相互作用会导致鳗鱼等物种的种群数量进一步下降,而过度捕捞或环境变化又会使这些物种变得脆弱。此外,营养级之间的相互作用可能会进一步导致鳗鱼种群的崩溃,但人们对这一点还知之甚少,尤其是在西印度洋(WIO)河流沿岸。这项研究评估了在排入西印度洋的阿蒂河和拉米西河用玻璃网和商业刺网捕获的鱼类的胃内容物。使用解剖显微镜检查胃内容物,以确定食物组成。鳗鱼主要摄食各种鱼类(43%)和甲壳类(36%),如对虾(14%)、对虾(13%)和螃蟹(9%),因此其营养级(TL)为3.47,高于本地鱼类(2.98)或引进鱼类(2.8)。鳗鱼的食物广度(0.20)明显低于同域鱼类(0.27),这归因于其较高的食物专一性。肉食性鱼类的TL(3.19)和它们的食物与鳗鱼的TL(3.19)相比较,尽管不同种类鱼类对食物的偏好有很大差异。因此,被世界自然保护联盟列为易危物种的鳗鱼正受到肉食性鱼类的进一步威胁。
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引用次数: 0
Feeding habits and diet composition of Octopus cyanea (Gray, 1849) in Zanzibar waters, Tanzania 坦桑尼亚桑给巴尔水域的章鱼胞囊(Gray,1849 年)的食性和食物组成
Pub Date : 2023-11-09 DOI: 10.4314/wiojms.v22i2.5
Amini I. Hamad, Christopher A. Muhando
The octopus fishery in Zanzibar is an essential activity of coastal communities. To assist with developing fisheries management plans, baseline information on the feeding of Octopus cyanea (Gray, 1849) was collected in relation to sex and maturity stages. The feeding habits and diet composition of 543 O. cyanea were studied over a period of 12 months at Paje, Kizimkazi, Chwaka Bay and Nungwi. Samples at each site were collected on two days per month during spring tide. Digestive tract contents revealed that O. cyanea preyed on 36 species of crustaceans, molluscs and fishes, with crabs a major prey item. The number of prey species in a single stomach ranged from one to six. O. cyanea in Zanzibar is therefore a generalist predator with a mixed diet. The octopus gonadosomatic index (GSI) indicated a peak breeding season in June to October, which correlated with low prey consumption. Mature octopuses ingested a small amount of food from mainly small sessile prey. Females consumed less food than males of similar maturity stages, suggesting that they ate less or had higher digestion rates. The information is useful for developing fisheries management plans for the octopus fishery in Zanzibar.
桑给巴尔的章鱼渔业是沿海社区的一项重要活动。为了协助制定渔业管理计划,我们收集了有关章鱼(Octopus cyanea,Gray,1849 年)摄食与性别和成熟阶段的基线信息。在 Paje、Kizimkazi、Chwaka Bay 和 Nungwi,对 543 只 O. cyanea 的摄食习惯和食物组成进行了为期 12 个月的研究。每个地点的样本都是在春潮期间每月两天采集的。消化道内容物显示,O. cyanea捕食了 36 种甲壳类、软体动物和鱼类,其中螃蟹是主要的猎物。一个胃中的猎物种类从 1 种到 6 种不等。因此,桑给巴尔的 O. cyanea 是一种混合食物的食肉动物。章鱼性腺指数(GSI)表明,章鱼的繁殖旺季在 6 月至 10 月,这与猎物消耗量低有关。成熟章鱼主要从小型无梗猎物中摄取少量食物。雌性章鱼消耗的食物少于成熟阶段相似的雄性章鱼,这表明它们吃得更少或消化率更高。这些信息有助于制定桑给巴尔章鱼渔业管理计划。
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引用次数: 0
Lessons for ensuring continued community participation in a mangrove blue carbon conservation and restoration project in Madagascar 确保社区持续参与马达加斯加红树林蓝碳保护和恢复项目的经验教训
Pub Date : 2023-11-06 DOI: 10.4314/wiojms.v22i2.4
Lalao A. Ravaoarinorotsihoarana, Jenny Maltby, Leah Glass, Jenny Oates, Cicelin Rakotomahazo, Dolce A. Randrianandrasaziky, Lanto Ranivoarivelo, Thierry Lavitra
Successful conservation projects that restrict or change access to common pool resources require meaningful community participation not only through consultation but also by empowering communities to take a leading role from the early stages of its design. In this study, community participation was assessed in the Tahiry Honko community-led mangrove blue carbon project in southwest Madagascar using the Spectrum of Public Participation tool developed by the International Association for Public Participation. Trends of community participation at village meetings were assessed using the meeting records from 2014 to 2019. Performance in the project activities was assessed based on the indicators of success. It was learned that: (i) careful scheduling of meetings is crucial to avoid community fatigue; (ii) anonymous democratic votes are an effective, inclusive approach to address domination in a group activity and obtain informed consent; (iii) creating a comfortable space for women is vital to promote their participation in decision-making; (iv) voluntary approach with meal compensation is effective to engage all community groups in mangrove replanting; (v) competitive process is crucial to recruit motivated volunteers for mangrove forest patrols; and (vi) dissemination of patrol results is helpful in developing an adaptive strategy in the absence of effective enforcement of rules.
成功的保护项目会限制或改变对公共资源的获取,这就需要社区的切实参与,不仅要通过咨询,还要从项目设计的早期阶段就赋予社区主导权。在本研究中,使用国际公众参与协会开发的 "公众参与光谱 "工具,对马达加斯加西南部由 Tahiry Honko 社区主导的红树林蓝碳项目的社区参与情况进行了评估。利用 2014 年至 2019 年的会议记录评估了社区参与村级会议的趋势。根据成功指标评估了项目活动的绩效。据了解(i) 精心安排会议时间对于避免社区疲劳至关重要;(ii) 匿名民主投票是一种有效的包容性方法,可以解决群体活动中的支配问题并获得知情同意;(iii) 为妇女创造舒适的空间对于促进她们参与决策至关重要;(iv) 采用自愿的方式并给予餐费补偿,可有效地让所有社区团体参与红树林补种;(v) 竞争过程对于招募积极的志愿者参与红树林巡逻至关重要;(vi) 在缺乏有效执行规则的情况下,传播巡逻结果有助于制定适应性战略。
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引用次数: 0
Hydrodynamics of nearshore coastal waters: Implications for marine cage farming in Kenya 近岸沿海水域的水动力学:对肯尼亚海水网箱养殖的影响
Pub Date : 2023-10-26 DOI: 10.4314/wiojms.v22i2.3
D. Mirera, Athman Salim, Joselyne Kendi
Hydrodynamic characteristics are important considerations in the design of cages used for fish farming in nearshore marine environments. The hydrodynamics of sites in mangrove creeks and comparatively open water channels in Kilifi and Kwale Counties in Kenya were sampled across tidal cycles and seasons using an Acoustic Wave and Current Profiler (AWAC). Water temperature ranged between 25.9 °C and 33.0 °C, and was lower in deeper areas with larger tidal heights than in shallower areas with smaller tidal heights. The water column height ranged between 9.68 - 14.69 m at Kijiweni, 1.16 - 6.7 m at Kibokoni and Tsunza, and 0.72 - 2.57 m at Dabaso. Maximum current speeds were 0.83 - 0.87 m/s at Kijiweni, 1.1 m/s at Kibokoni, 0.89m/s Tsunza, and 0.34 m/s at Dabaso. Wave height reached 0.35 and 0.36 m at Kijiweni, 2.7 m at Kibokoni, 1.3 m at Tsunza, and 1.6 m at Dabaso. The considerable difference in hydrodynamic characteristics between the sampling sites indicate that cages for marine fish farming should be designed specifically for local conditions in mangrove creeks and Cages for fish farming therefore require specific design and structural features depending on the local hydrodynamic conditions.
水动力特性是设计近岸海洋环境中养鱼网箱的重要考虑因素。使用声波海流剖面仪(AWAC)对肯尼亚基利菲县和夸莱县的红树林溪流和相对开阔水域渠道的水动力特征进行了采样,采样跨越了潮汐周期和季节。水温介于 25.9 °C 和 33.0 °C 之间,潮汐高度较大的深水区水温低于潮汐高度较小的浅水区。基吉韦尼的水柱高度介于 9.68 米至 14.69 米之间,基博科尼和松扎的水柱高度介于 1.16 米至 6.7 米之间,达巴索的水柱高度介于 0.72 米至 2.57 米之间。基吉韦尼的最大流速为 0.83 - 0.87 米/秒,基博科尼为 1.1 米/秒,Tsunza 为 0.89 米/秒,达巴索为 0.34 米/秒。基吉韦尼的波高分别为 0.35 米和 0.36 米,基博科尼为 2.7 米,松扎为 1.3 米,达巴索为 1.6 米。取样地点之间水动力特征的巨大差异表明,海鱼养殖网箱应根据红树林溪流的当地条件进行专门设计。
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Western Indian Ocean Journal of Marine Science
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