Distribution of Five Macrobrachium Species Along a Salinity Gradient in Rivers State Nigeria

  • Adaba Ibim

Abstract

A study was carried out to determine the distribution of five Macrobrachium species M.dux M.vollenhovenii M.macrobrachion M.felicinum and M.equidens along a Salinity gradient in the New Calabar and the Bonny Rivers in Rivers state. The aim was to identify the preferred salinity range and tolerance of these species in the field. Subsequently a five-month field survey was conducted in six sample stations along the Bonny and New Calabar Rivers. Once weekly the Salinity regime of the sample stations was determined by ascertaining the Salinities of the water samples from the stations using a Salinometer and by the criteria of Rogers et al. 2003. Simultaneously Prawn samples were collected from the stations using indiscriminate nets and traps identified and their distributionrange and abundance in the stations assessed using standard methods. Results revealed the Salinity gradient in the stations along the Bonny and New Calabar Rivers with Isiokpo as Freshwater 0 ppt Aluu and Choba Oligohaline 0ppt to 1ppt and 1ppt to 4ppt respectively Rumuokparali 10ppt and 14ppt and Ogbogoro 14ppt and 16ppt being Mesohaline. Bakana 16ppt and 18ppt fluctuates between meso- and polyhaline while the Isaka area is Polyhaline 20ppt and 25ppt. The identification of the different species of the Macrobrachium their distribution and abundance in the Salinity gradient showed that the M.equidens are Polyhaline existing between 15ppt to 24ppt. M. macrobrachion in 0ppt to 15ppt and M. vollenhovenii in 0ppt to 16ppt are euryhaline species cutting across a wide Meso to Oligohaline environment. M. felicinum found in 0ppt to 1ppt waters and M. dux in 0ppt waters only are Oligohaline and Freshwater species respectively. It was observed that all these species especially M. equidens have distribution patterns which vary from their distribution in other rivers globally. Secondly the M. vollenhovenii and M. macrobrachion species occupy thesame salinity gradient but are prominent at different times of the day with M. macrobrachion more active in the day and the M. vollenhovenii at night time. In conclusion the Bonny and New Calabar Rivers stretch showcases a Salinity gradient ranging from brackish to fresh waters. The different Macrobrachium species are prevalent in this Salinity gradient. However their abundance and distribution vary widely along this gradient. The reason for this variation is not known but it is suspected to be as a result of several biotic or abiotic factors that interplay and not salinity alone. It is therefore recommended that studies of several abiotic and biotic factors be carried out simultaneous to ascertain the true reason for the variation along this Salinity gradient and other habitats where they occur. This will go a long way in understanding their biology culture and the management of the fishery of these economically important species.
Published
2018-12-06