Diet, size and reproductive biology of the silver catfish, Chrysichthys nigrodigitatus (Siluformes: Bagridae) in the Cross River, Nigeria

Abstract

The silver catfish, Chrysichthys nigrodigitatus (Lacépède: 1803) is a highly valued food-fish included among the dominant commercial catches exploited in major rivers of Africa. To provide useful biological data for management, samples were collected monthly between January (2005) and December (2007) in three zones: I: Upper Cross River (grassland), II: Middle Cross River (mixed forest and grassland), and III: Lower Cross River (rainforest)] along 200 km length of the Cross River, Nigeria. Data from 1 248 specimens were processed using: allometric coefficient (b), gonado-somatic index, Fulton's condition factor and diversity indices. Male dominance was observed in all populations; C. nigrodigitatus reached maturity at 11.5cm (male) and 16.7cm (female) total length. Gonado-somatic index was higher for females with a peak in the early rains. The breeding period was between April and August with mean fecundity ranging between 4522 ±1924 eggs and 20321 ± 5543 eggs. This was directly related to total length and weight by the regression models: F = 2365.88 + 560.22 log L and F = 5025.81 +56.34 log W respectively. Exponential equations for length-weight relationships were Wt=-1.997 Lt 2.206 (Zone I), W = -2.831 Lt 3.040 (Zone II) and Wt= -2.245 Lt 2.995 (Zone III). The mean allometric coefficient (b) showed significant departure from cubic value (negative allometry) for Zone I while Zones II and III showed no difference, indicating isometry. Dominant items in the diet were fish and fish parts constituting 21.6% with Food Richness and Gut Repletion Index of 18 and 100% respectively, in all zones. Diet Breadth of 0.802 (Zone I), 0.922 (Zone II) and 0.910 (Zone III) indicate a high trophic flexibility that enables switching from one diet to another according to availability. Mean condition factor for males varied from 0.718 ±0.117 minimum in Zone I to 0.996 ±0.062 maximum in Zone III. Forest inland wetlands (Zone II and III) of Cross River provided better condition for C. nigrodigitatus. Rev. Biol. Trop. 56 (4): 1785-1799. Epub 2008 December 12.

Diet and Food Consumption of the African Catfish, <i>Chrysichthys nigrodigitatus</i> Lacépède (1803) (Siluriformes: Claroteidae), from the Hydrosystem Lake Togo-Lagoon of Aného (South of Togo)

“…It can be explained by the fact that the fishing gear was not installed near the breeding grounds [19]. These results are similar to those obtained for the same species in some aquatic ecosystems in Nigeria [19] [31] [47]. However, they differ from those reported by Vanderpuye [17] in Volta Lake.…”

“…Analysis of the sex ratio of C. nigrodigitatus in Lake Togo-Lagoon of Aného showed that the number of males was significantly higher than that of females. It can be explained by the fact that the fishing gear was not installed near the breeding grounds [19]. These results are similar to those obtained for the same species in some aquatic ecosystems in Nigeria [19] [31] [47].…”

“…These apparently contradictory results could be attributed to partial segregation of mature forms through habitat preferences and migration or behavioral differences between sexes rendering one sex more easily caught than the other [46]. According to Offem et al [19], males migrate more frequently from breeding grounds to feeding areas located in shallow parts of the water body where they become vulnerable to be captured. Also, they suggest that females could take more shelter for incubation and protection of their offspring.…”

“…In the different ecological conditions in which they may live, they will find food that suits them [19] [62] [63]. The presence of mud and sand in the stomachs of these fish could be due to accidental ingestion along with other foods [64].…”

“…Studies on the fauna in inshore habitats revealed that Chrysichthys spp could represent, at certain periods of the year, the highest biomass of the littoral ichthyofauna, accounting for 17% to 43.8% of total catches [5] [16] [17]. The most recent works on feeding ecology come mostly from the lagoons and rivers of Ghana [18] and Nigeria [15] [19] [20] [21]. In Togo, studies on the bioecology of fish, which have mostly been limited to the description of fisheries, are very rare and old [14].…”