Abstract
Propagation in fishes depends on the level of gonad maturation which could be influenced by environmental conditions. However, declining water quality due to environmental degradation has been identified as a hindrance to such ecosystem services in aquatic ecosystems. Therefore, size distribution and stages of gonad development of P. obscura in relation to physic-chemical parameters of Eleyele reservoir were studied. Samples of water and Parachanna obscura were collected monthly from five stratified sampling points and fishers catch, respectively for 24 months. Fish were grouped according to sizes (10-15.9, 16.0-19.9 and ≥ 20 cm), and gonads assessed for maturation. Relationship between reproductive indices and physic-chemical parameters were determined using Principal Component Analysis. The size-groups distributions were 10-15.9 cm (28.6%), 16.0-19.9 cm (38.7%) and ≥ 20 cm (32.7%). All the five maturation stages (I-V) were discerned in the female while only stages II-IV were observed in male samples. All the size groups showed strong associations with pH (β=0.346), ammonia (β=0.303) and temperature (β=0.161). Ovary development was significantly influenced by DO (β=0.827), TDS (β=0.777) and TS (β=0.813), while testes maturation was more influenced by temperature (β=0.626). This information will serve as guides for effective ecosystem management through the control of anthropogenic activities on this reservoir and similar water bodies to enhance resource conservation and/or sustainable management.
Highlights
IntroductionLakes and reservoirs constitute very important nursery and breeding grounds for a large variety of fish species, making it crucial to feeding millions of people around the globe
Eleyele reservoir, located in Ibadan North-West area of Ibadan metropolis, Nigeria lie at Latitude 7 ̊25'0''–7 ̊26'15'' N and Longitude 3 ̊50'45''–3052'15'' E
Dirican, Lewis and Rakocinski et al, reported the existence of a good correlation between surface temperature and the fish population structure, suggesting that aquatic organisms depend on certain temperature range for their optimal growth
Summary
Lakes and reservoirs constitute very important nursery and breeding grounds for a large variety of fish species, making it crucial to feeding millions of people around the globe. The reservoir was spatially stratified into five zones as S1–S5 based on hydrological features, for water sampling following Kareem and APHA [12,13]. Samples of P. obscura were bimonthly collected from fishers catch. Water variables measured includes dissolved oxygen (mg/L), water temperature (°C), pH, chemical oxygen. Demand (mg/L), total solid (mg/L), total dissolved solid (mg/L), conductivity (μS cm-1), nitrate (mg/L), nitrite (mg/L), ammonia (mg/L), calcium (mg/L), magnesium (mg/L), sulphate (mg/L), phosphate (mg/L), mean depth (m). Fish were grouped according to sizes following the method of Ayinla [14]. The data collected were analyzed using descriptive statistics, Spearman rank correlation and Principal Components Analysis (PCA) using PAST programme [16,17,18]
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