6. Seasonal changes in stream habitat structure and its relationship with fish community structure in a low gradient stream in Sunyani, Ghana

Abstract

Studies on seasonal changes in stream structure and its effect on habitat quality, distribution, abundance and biomass of stream fishes in Ghana is limited. Understanding seasonal changes in stream habitat structure and adaptive responses of fish populations is essential for stream protection and conservation of stream ecosystems and their resident fish populations. Seasonal changes in stream structure, physicochemical characteristics and fish community structure were investigated in an urban stream in Sunyani, Ghana. Data was collected monthly from November 2016 to November 2017 at upstream, midstream and downstream sites. High spatial heterogeneity and temporal variability in stream structure affected by the dry and wet seasonal cycles was observed. Twelve species of fish belonging to eight families and ten genera were recorded, with catfishes dominating community biomass. The diet pattern of fish species differentiated the community into herbivore, piscivore and omnivore trophic levels. Herbivores were most abundant and consumed a wide range of plantbased food. Fish habitats disappeared and mortality increased upstream and midstream during the dry season. However, the downstream habitat persisted as a result of the unique morphology which resulted in a relatively deep depth, large canopy cover and presence of water lettuce Pistia stratiotes which minimized water loss. Water quality did not differ significantly across the stream in all seasons. Higher water clarity downstream cooccurred with Pistia proliferation along with elevated fish biomass during the dry season. Stream structure, rather than physicochemical characteristics, controlled fish biomass. Water quality and fish biomass were strongly correlated with seasonal Pistia abundance. Persistence of the downstream pool habitat during the dry season sustained habitat quality and increased fish survival. Maintenance of stream pools along with opportunistic aquatic vegetation in the dry season can sustain stream ecosystems and stabilize their fish communities and biotic structure.