Gerres

Abstract: Mitochondrial genome is a powerful molecule marker to explore phylogenetic relationships and reveal molecular evolution in ichthyological studies. Gerres species play significant roles in marine fishery, but its evolution has received little attention. To date, only two Gerres mitochondrial genomes were reported. In the present study, three mitogenomes of Gerres (Gerres filamentosus, Gerres erythrourus, and Gerres decacanthus) were systemically investigated. The lengths of the mitogenome sequences were 16,673, 16,728, and 16,871 bp for G. filamentosus, G. erythrourus, and G. decacanthus, respectively. Most protein-coding genes (PCGs) were initiated with the typical ATG codon and terminated with the TAA codon, and the incomplete termination codon T/TA could be detected in the three species. The majority of AT-skew and GC-skew values of the 13 PCGs among the three species were negative, and the amplitude of the GC-skew was larger than the AT-skew. The genetic distance and Ka/Ks ratio analyses indicated 13 PCGs were suffering purifying selection and the selection pressures were different from certain deep-sea fishes, were which most likely due to the difference in their living environment. The phylogenetic tree was constructed by molecular method (Bayesian Inference (BI) and maximum Likelihood (ML)), providing further supplement to the scientific classification of fish. Three Gerres species were differentiated in late Cretaceous and early Paleogene, and their evolution might link with the geological events that could change their survival environment.

Abstract: Assessing the ecological status of rivers, creeks, and streams is a fundamental and increasingly important water management issue worldwide. This study examines the variations in fish community structure along an increasing pollution gradient in a small Niger Delta creek in Nigeria in both time and space. Salinity of the area fluctuated between fresh and mesohaline brackish waters with values ranging from 0.4 to 5.2 PPT and electrical conductivity values ranging between 16.9 and 136.0 µS/cm. The site in the upper creek (Site 1) was relatively free from gross pollution, with significantly high dissolved oxygen levels and low nutrient and salinity levels. Site 3 recorded relatively higher values of 5-day biochemical oxygen demand (BOD5) and high nutrient levels, indicating substantial input of organic matter to the creek upstream. Six (6) species, Tilapia guineensis (Cichlidae), Bostrychus africanus (Eleotridae), Hemichromis fasciatus (Cichlidae), Ethmalosa fimbriata (Clupeidae), Gerres melanopterus (Gerreidae), and Clarias macromystax dominated the sample and accounted for about 70 % of the total catch. Tilapia guineensis constituted the major dominant species and accounted numerically for about 20 % of the total catches and 45 % of the total biomass. Multi-species fisheries dominate the coastal zone with Tilapia guineensis, Gerres melanopterus and Ethmalosa fimbriata, Liza falcipinus, Mugil spp., and Chrysichthys nigrodigitatus, the major species in the commercial catches. Canonical correspondence analysis indicated that dissolved oxygen, electrical conductivity, total nitrogen, BOD5, and temperature were important variables structuring the overall fish assemblages. Overall, salinity was the major environmental variable determining the diversity of fish communities at the various sites. The effect of anthropogenic activities and land use practices around the creek only marginally affected the abundance of the fish species but not the diversity. These findings indicate that the water body is still useful as a good fishing ground for the rural communities and every effort should be put in place to ensure its protection and conservation for the production of healthy fish.