Temporal patterns in the density and feeding ecology of gobies, Asterropteryx semipunctatus and Gnatholepis sp.1 in East African mangrove ecosystem (Gazi Bay, Kenya)
Ndede, R.O. (1998). Temporal patterns in the density and feeding ecology of gobies, Asterropteryx semipunctatus and Gnatholepis sp.1 in East African mangrove ecosystem (Gazi Bay, Kenya). MSc Thesis. KUL: Brussel. VIII, 97 pp.
To understand the 24hrs (temporal) pattern in the density distribution and the consumption of prey items (food), for Asterropteryx semipunctatus and Gnatholepis sp.1 (Pisces, Gobiidae) an investigation was carried out in the sub-tidal Western creek of the Gazi bay (Kenya) between July and October 1995. In order to investigate a semi-lunar pattern, ten twenty-four hour cycles were sampled at consecutive spring and neap tides. A total of 480 (10 sampling x 12 sampling times x 4 locations) cases were collected. Two hours samplings consisted of 4 hauls with duration of 10 minutes and mean distance of 300m. Generally, catches for Gnatholepis spl were more during the day as compared to the night catches. Catch rates for Asterropteryx semipunctatus varied irregularly during 24hr periods without clear pattern of the day and night preference in density distribution. Densities of both Gnatholepis sp.1 and Asterropteryx semipunctatus were not affected by sampling locations. There was no correlation between the densities and the tidal phases for both species. However, there was weak tendency for high catch rates during high water heights for Asterropteryx semipunctatus and low water heights for Gnatholepis sp.1. But no significant difference in density by water height was observed for the two species. Lunar phases had influence in the catch rate of Gnatholepis sp.1 and Asterropteryx semipunctatus but in different ways. Members of Gnatholepis sp.1 were caught in higher numbers during the spring tide while Asterropteryx semipunctatus during neap tides. Analysis of stomach fullness index revealed that feeding activities of Gnatholepis sp.1 were on average concentrated between sunrise (6.30hrs) and sunset (18.05hrs). The maximum fullness index was reached at 14.00hrs and 18.00hrs. Feeding stopped at night from 18hrs. In general Gnatholepis sp.1 is a day feeder exhibiting discrete feeding pattern. Asterropteryx semipunctatus feed throughout day and night. Asterropteryx semipunctatus exhibits continuous feeding pattern with more day and less night feeding activity. Locality had no influence in the fullness index of both the species of study. Likewise there was no influence in the fullness index by tidal phases (low tide, incoming tide, high tide and outgoing tides). Lunar phases affected the feeding habit of Gnatholepis sp.1 where by the fullness index was high in the spring than neap tides. Stomach content analysis revealed that Asterropteryx semipunctatus and Gnatholepis sp.1 consumed a wide range of prey items typical of tropical Gobiid species. The important prey species for both fish species were Amphipods, copepods and isopods. However the relative importance of the species did not vary with the time of the day when feeding took place. Amphipod was the most important prey item numerically and volumetrically for Asterropteryx semipunctatus throughout the 24hrs cycle. In the case for Gnatholepis sp.1 copepods were the most important numerically while amphipods were most important volumetrically over the 24hrs cycle. There was low variability (Simpsons diversity index) in the prey item consumed by Asterropteryx semipunctatus over 24hrs cycle.
Dataset
Ndede R.O.; Ollevier F.; Fundamental and Applied Marine Ecology Post Graduate Program (FAME). VUB; Laboratory of Ecology and Aquaculture, Zoological Institute. KUL: Belgium; (2015): Temporal patterns in density and feeding ecology of Asterropteryx semipunctatus and Gnatholepis sp.1 in Gazy Bay (Kenya) in 1995., meer
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