加强撒哈拉以南非洲鱼类苗种系统的制约因素与干预策略：来自加纳的证据

本研究针对撒哈拉以南非洲地区鱼类苗种系统运行机制不明、制约因素不清的问题，以加纳为案例开展罗非鱼苗种价值链分析。通过混合研究方法评估了种质资源基础、苗种生产质量、供应分配体系及信息流等维度，发现种质退化、生物安全管理薄弱、运输损耗高等关键瓶颈。研究验证了技术援助与亲本分发、苗圃建设、ICT工具应用及农户培训等干预措施的有效性，为区域水产养殖可持续发展提供了政策依据和实践路径。

　　

aquaculture has emerged as the world's fastest-growing food production sector, offering significant potential to enhance food security, alleviate poverty, and promote environmental sustainability. However, in sub-Saharan Africa, the development of aquaculture faces critical constraints, particularly in the fish seed system. Fish seed, comprising hatchlings, fry, fingerlings, or juveniles, serves as the foundation for productive and profitable aquaculture. Unlike crop seeds, fish seed is a delicate living material that requires meticulous handling, specialized transportation with oxygen systems, and complex management practices involving broodstock care, water quality control, and stringent biosecurity measures. These requirements make fish seed production more expensive, challenging, and risky. Despite its importance, there is a notable scarcity of research on fish seed systems and value chains in sub-Saharan Africa, with most available studies being descriptive and lacking rigorous impact evaluations. Ghana, as the top producer of farmed tilapia in the region, presents an ideal case to explore these issues. The country's aquaculture sector has experienced rapid growth driven by large-scale cage farming on Lake Volta, but recent stagnation has been largely attributed to seed-related problems, including poor maintenance of germplasm base, inferior seed quality, limited availability, lack of information coordination, and weak enforcement of regulations. The Ghana Tilapia Seed Project (TiSeed), implemented from 2019 to 2022, aimed to address these gaps by analyzing the challenges and opportunities along the fish seed value chain and testing promising interventions to strengthen the system.

To conduct this comprehensive study, researchers employed a mixed-methods approach, integrating quantitative and qualitative techniques. The analytical framework, adapted from Shikuku et al. (2021b), focused on four key components: germplasm base, seed production and quality, seed availability and distribution, and information flow. Primary data were collected through surveys and interviews with various actors in the fish seed value chain across seven major aquaculture regions in Ghana. Baseline surveys in 2019 engaged 45 hatchery operators, 10 nursery operators, and 603 grow-out farmers, including both active and exited farmers. Follow-up surveys from 2020 to 2022 tracked changes and impacts. Participatory action research (PAR) was utilized to engage hatchery operators in profitability analysis and management practice improvements. Additionally, performance trials were conducted to determine optimal fingerling sizes (2 g, 5 g, and 10 g) and transportation durations (3, 4, and 5 hours) under controlled conditions, monitoring survival rates and water quality parameters. Impact evaluations included propensity score matching and inverse probability weighted regression adjustment to assess the effectiveness of information and communication technology (ICT) tools, such as mobile phones, TV, and radio, in disseminating aquaculture advice. Difference-in-difference (DID) estimation and cluster randomized controlled trials were applied to evaluate training interventions on feed formulation and good aquaculture management practices. These methods allowed for a robust analysis of interventions aimed at enhancing seed system efficiency and sustainability.

^{4.1. Bottlenecks}

^{4.1.1. Germplasm base}

The study identified a significant bottleneck in the weakening fish strain and broodstock available in Ghana. Most tilapia farmers use the local Akosombo strain of Nile tilapia (Oreochromis niloticus), which was first developed in the early 2000s and is the only legally permitted strain. However, the strain has remained at its 11th generation since 2016 due to funding discontinuation and limited technical capacity, while strains in other countries have advanced to the 21st generation. This stagnation has led to reduced performance and stress resistance. Many hatchery operators illicitly introduce exotic strains, such as the genetically improved farmed tilapia (GIFT) from Asia or the genetically improved Abbassa Nile tilapia (GIANT) from Egypt, which offer better growth performance but pose risks of disease and mass mortality, as observed in 2019. Molecular mapping studies confirm the presence of these exotic strains, highlighting the urgent need for policy reforms and capacity building in strain development and broodstock management.

^{4.1.2. Seed production and quality}

From the perspectives of grow-out farmers and hatchery operators, seed production and quality face numerous challenges. Farmers reported issues such as lack of fingerling uniformity, incomplete sex reversal leading to growth disparities, and high mortality rates during transport and stocking. Hatchery operators cited high feed costs, poor technical knowledge, and inadequate biosecurity measures as major constraints. Baseline assessments revealed that many hatcheries did not follow recommended protocols for quality fingerling production, resulting in low efficiency in hormonal sex reversal, grading, and conditioning. Additionally, high costs of fuel and electricity, limited access to finance, and water quality issues further hampered hatchery operations. Trust in suppliers emerged as a critical factor due to the credence nature of seed quality, emphasizing the importance of relationships along the value chain.

^{4.1.3. Seed availability and distribution}

Seed handling and transportation were identified as critical factors affecting fingerling survival. Fingerlings were typically transported using open or closed systems, but hatchery operators lacked specialized vehicles, relying on personal or hired transport. The average size of tilapia fingerlings supplied decreased from 10–30 g to 1–2 g over the past decade, increasing susceptibility to stress and prolonging growth periods. Mortality rates during transportation and stocking ranged from 5% to as high as 75–99%, indicating severe inefficiencies in distribution channels. The absence of specialized services, such as seed agents and traders, unlike in Bangladesh, limited the accessibility of quality seeds for small-scale farmers.

^{4.1.4. Information flow}

Information dissemination through extension services and ICT tools was inadequate. Fisheries Commission (FC) extension agents were limited in number and accessibility, and farmers perceived their advice as outdated. While mobile phones and TV were widely used, only 63% of farmers received aquaculture advice through mobile phones, and even fewer through TV or radio. This underutilization of ICT resources highlighted a gap in delivering timely and relevant information to farmers, affecting their ability to adopt improved management practices.

^{4.2. Promising approaches}

^{4.2.1. Technical assistance and broodstock distribution to hatcheries}

The provision of bundled services, including technical assistance, group trainings, and free broodstock (G11 Akosombo strain), significantly improved hatchery operations. Out of 30 hatcheries supported, 15 reported major improvements in production and compliance with good biosecurity and management practices (GBMPs). The distribution of new broodstock enhanced spawning rates and fingerling quality, leading to increased sales and customer confidence. Profitability analysis showed positive margins for hatcheries of all sizes, though very small hatcheries required subsidies to break even. However, overall compliance with GBMPs remained low at 40%, indicating the need for continuous coaching and monitoring.

^{4.2.2. Optimal practices and fingerling size for transportation and handling}

Performance trials revealed that 10 g fingerlings had the highest survival rates during transportation and after stocking, regardless of duration. Shorter transportation times (3 hours) resulted in less than 1% mortality. Recommendations included regular water flushing, reduced stocking density in conditioning hapas, and swift packaging to minimize handling stress. These findings emphasized the importance of optimal fingerling size and transportation practices in reducing mortality and improving productivity.

^{4.2.3. Nursery establishment}

The establishment of nurseries in remote areas decentralized fingerling production and improved access for grow-out farmers. Ten nurseries were set up, operated by both hatchery operators and grow-out farmers, resulting in profit margins increasing by 35–66%. Nurseries required less capital investment than hatcheries and were met with high demand from communities, highlighting their potential to enhance seed availability and reduce transportation costs.

^{4.2.4. ICT tools}

The use of ICT tools, particularly mobile phones and TV, significantly improved farmers' recordkeeping, biosecurity practices, productivity, and profitability. Farmers using ICT tools harvested 0.5 kg more fish per square meter and earned 3 Ghanaian cedi more per square meter. When combined with FC extension services, the impact was even greater. A WhatsApp platform, FishConnect, facilitated market linkages but had low participation rates (10%), suggesting the need for expanded implementation and updated content.

^{4.2.5. Farmers' training on feed formulation}

Training sessions on feed formulation using locally available materials reduced feed costs, which account for 70–80% of production expenses. The training led to an additional profit of 1032 cedi (US$160) per pond annually, with a rate of return on investment of 1500–1900%. This intervention proved especially beneficial for small-scale farmers with limited financial resources, enabling them to maintain feeding intensity and improve productivity.

^{4.2.6. Farmers' training in good aquaculture practices}

Cluster-based training sessions incorporating field visits to model farms enhanced farmers' management practices, resulting in an increase of 0.45 kg of fish harvested per square meter and an additional income of US$627 per trainee annually. The training provided a 300–600% rate of return on investment, demonstrating its cost-effectiveness and potential for scaling across Ghana and similar contexts.

The study concludes that bottlenecks in Ghana's fish seed system span the entire value chain, from germpl degradation to information gaps, significantly hampering aquaculture growth. Interventions such as technical assistance, broodstock distribution, nursery establishment, ICT tools, and farmer training have proven effective in addressing these constraints. These approaches not only improved seed quality and availability but also enhanced productivity and incomes for hatchers and grow-out farmers. However, sustained efforts are needed to ensure compliance with biosecurity standards and to address the underlying issue of strain stagnation. The findings underscore the importance of policy reforms, including the adoption of national guidelines for exotic strain introduction and strengthened regulatory enforcement. Capacity building at all levels, from strain management to farmer training, is crucial for sustainable aquaculture development. The study's mixed-methods approach and rigorous evaluation provide valuable insights for policymakers, researchers, and practitioners aiming to strengthen fish seed systems in sub-Saharan Africa. By highlighting both the bottlenecks and promising interventions, this research offers a pathway to transform aquaculture into a more productive, profitable, and sustainable sector, contributing to food security and economic development in the region.