Understanding tilapia mortalities and fish health management in Lake Volta: a systematic approach

Abstract

Unusual fish mortalities in aquaculture threaten global food security and carry significant socio-economic burdens. In 2018, Nile tilapia (Oreochromis niloticus) suffered unusual patterns of mortalities, attributed to disease-causing agents in Lake Volta cage aquaculture. In recent times, disease investigations have shifted from single to consideration of multiple factors to understand the puzzling range of causal risk factors. This study therefore aimed at expanding on tilapia mortality risk factors, while documenting fish health and Lake Volta management practices for sustainable aquaculture. We interviewed relevant aquaculture stakeholders operating on Lake Volta and conducted thematic analysis on their responses to map out mortality risk factors and management practices. The identified risk factors were conceptualized in established models of causation web and Social-Ecological System to explain the practical significance of the findings. The results showed that the risk factors of tilapia mortalities are a combination of pathogens and non-infectious factors mediated by weak law enforcement. The results further suggested mortality reinforcing mechanisms through the horizontal transmission of pathogens, namely, Streptococcus agalactiae and Infectious Spleen and Kidney Necrosis Virus. Moreover, the recognition of weak enforcement as a possible factor reinforcing human activities is a non-infectious route that can be deleterious to fish health. Health management practices comprised phytotherapy, vaccination, heat shock treatment, biological controls, and best husbandry practices. Lake management involves creating a waterfront buffer of 85.34 m, surveillance, and executing the framework guiding aquaculture development on the Lake. The findings are suggestive of complementary quantitative studies that augment the qualitative evidence herein. Such follow up studies can disclose precise mortality risk factors to inform policy directives and effective remedial strategies that can secure fish and lake health.

Stakeholder perspectives on the 2023 Ghana National Aquaculture Development Plan: An integration within the ecosystem approach framework

“…This includes the introduction of competitive species serving as vehicles of imported diseases (Table 2), corroborating the findings in Zornu et al. (2023). It is therefore imperative to initiate selective breeding programmes towards developing quality aquaculture seeds in Ghana.…”

“…External factors exacerbated by water pollution through human activities are also documented as part of the pitfalls (Table 2). A classical example is the case of Lake Volta whereby human activities are perceived to be reducing water quality (Zornu et al., 2023). This can reduce the potential of the watershed in supporting aquaculture activities including its ecosystem services to communities that bothers it.…”

“…This can reduce the development of drug‐resistant bacteria and increase the effectiveness of antibiotic treatments. Alternative treatments through immunostimulants, namely β‐glucans plant‐based products such as neem tree leaves and ginger, to enhance the immune system are considered sustainable options (Collado‐González & Esteban, 2022; Machuca et al., 2022; Mohammadi et al., 2020; Zornu et al., 2023). Disease management was among the justifications as farmers treated infected fish in desperation (Table 3).…”

“…The answers for the open questions, numbered one to four, were collated for thematic analyses (Sarku et al., 2020; Zornu et al., 2023). This was done by realigning sentence structures followed by coding in Atlas.ti through reflexive and iterative processes to identify key responses on the various questions.…”

“…While increasing fish production is important for food security, it is imperative to ensure that efforts to boost production are accompanied by long‐term industry sustainability plans. The exclusive focus on enhancing fish production led to the introduction of exotic tilapia, perceived to be highly performing, yet, this species facilitated the infiltration of foreign pathogens into Ghana's aquaculture industry (Ramírez‐Paredes et al., 2021; Verner‐Jeffreys et al., 2018; Zornu et al., 2023). These pathogens carry socio‐economic burdens and ecological impacts, such as the financial losses from tilapia mortalities.…”