ARI Volume 2 Number 1.pdf - Zoo-unn.org

Salinity stress and buccal ventilatory rate in African lungfish 253Table 1: The salinities (%o) of the various concentrations of dilute seawater that werepreparedPrepared seawaterConcentration (%)Corresponding salinity(%o)Volume of dechlorinatedWater (litres)Volume of100% seawater (35 %o)40302015105014.0010.507.005.303.501.800.001.802.102.402.552.702.853.001.200.900.600.450.300.150.00diluted seawater at a stocking rate of twospecimens per tank.Buccal Ventilatory Rate: Only healthy andactive fishes with no external signs of disease orphysical injuries were selected for the experiment.The buccal ventilatory rate was estimated as thenumber of times each fish would remove its headout of the water, opened its mouth in order tobreathe atmospheric oxygen, closed it and dippedits head back into the water, within an hour. Thiswas repeated five times and the mean valuesnoted.RESULTSIncrease in salinity was directly correlated withincrease in buccal ventilatory rate Coefficient oflinear correlation r = 0.9162767 at 0.05 probability(Figure 1). At 0 %, 5%, 10 %, 15 %, 20 %, 30 %and 40 % salinities, the mean buccal ventilatoryrates were 4.04, 5.32, 6.39, 7.50, 9.86, 10.16 and12.26 respectively.Mean rates of buccalventilation141210864200 20 40 60Concentrations of dilutedseawaterFigure 1: The mean rates ofbuccal ventilation at variousconcentrations of dilutedseawaterDISCUSSIONThe result clearly indicates a positive linearcorrelation between salinity and buccal ventilatoryrate. Holliday (1969) reported reduction in oxygencontent of saline waters. The present study opinedthat the increased buccal ventilatory rate whenimmersed in saline water could be a means ofincreasing the total amount of oxygen that wouldreach the tissues via the lungs since the amountreceived from the saline water via the gills washighly reduced.Similar findings have been documented byEnajekpo (1989), Ebele et al. (1990), Onusiriukaand Ufodioke (1994), Chukwu (2001) and Chukwuand Ugbeva (2003). For example, Enajekpo (1989)reported an increase in respiration rate (opercularventilation) in Tilapia zilli and Oreochromisniloticus exposed to sublethal concentrations ofwater soluble fractions of Bonny light crude.Thus in the attempt to culture P.annectens in brackish or estuarine waters, farmersshould put into consideration the increaseddemand for atmospheric oxygen in the newhabitats. Since this process requires theexpenditure of energy, this may be compensatedby increasing the rate of feeding.There is no lungfish that naturally inhabitsbrackish or estuarine waters within this Cenozoicera. However, fossil records have established thatlungfishes that lived during the Permian,Carboniferous and Devonian periods such asGnathorhiza, Megapleuron and Soederberghiawere estuarine and shallow marine dwellers(Carroll, 1988; Ahlberg, et al., 2003).Soederberghia gulped air and probably inhabited ashallow near-shore marine environment (Ahlberg,et al., 2003). The occurrence of Soederberghiagroenlandica in the Famennian old red sandstoneof North America, Greenland and Australiarespectively thus furnishes evidence of contact orclose proximity between North and South Pangaeaduring the Palaezoic era (Ahlberg et al., 2003). Infact the evolution of air breathing by lungfisheshas traditionally been associated with their entryinto freshwaters (Carroll, 1988).REFERENCESAHLBERG, P. E., JOHANSEN, Z., ZERINA, J., andDAESCHLER, E. B. (2003). The lateDevonian lungfish, Soederberghia(Sarcopterygii, Dipnoi) from Australia and