Effect of salinity on oxygen consumption and growth of juvenile white steenbras, litohognathus lithognathus

Kandjou, K. (2009) Effect of salinity on oxygen consumption and growth of juvenile white steenbras, litohognathus lithognathus. Masters thesis, Rhodes University.

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Abstract

A stress-induced increase in metabolic rate of fish consumes energy within the metabolic scope of a fish that could otherwise be used for such functions as growth and reproduction. By estimating the degree of the metabolic response under given salinity levels and sudden changes thereof, it could be tested whether growth under given culture conditions could be predicted. Using intermittent respirometers, this study investigated the metabolic response of juvenile Lithognathus lithognathus following gradual acclimation to 5, 25 and 35‰ and, as a result of abrupt change from 35‰ to 5‰ or from 35‰ to 25‰ at 20˚C. The main aim of the study was to establish whether the magnitude of such responses could be used to predict growth of juvenile L. lithognathus under culture conditions. Hence, in addition to the respirometry study, two growth studies were conducted at 5, 10, 25 and 35‰ salinities. The baseline metabolic rates of juvenile L. lithognathus were also determined. Oxygen consumption measurements over 24-hours showed that most fish exhibited a diurnal peak in metabolic rates. The standard and active metabolic rates calculated from juvenile L. lithognathus with a diurnal peak in oxygen consumption were 0.06±0.001mgO2g-1h-1 (mean±SEM, n = 5), and 0.11±0.01mg O2g-1h-1, respectively. The standard and active metabolic rates of juvenile L lithognathus showing a nocturnal peak in metabolic activities were 0.04±0.001mgO2g-1h-1 (n = 1), and 0.12±0.003 mg O2 g-1 h-1, respectively. Routine metabolic rate of these fish calculated over a 3-h measurement period was 0.09±0.005mgO2g-1h-1 (n = 6). Juvenile L. lithognathus showed a relationship between metabolic rate (mo2) and body weight (W) following the equation: mo2 = 0.62 W-0.53. The effect of salinity changes on oxygen consumption rates of juvenile L. lithognathus revealed that abrupt change in salinity from 35‰ to 5‰ was the only treatment in which oxygen consumption was affected by time of measurement, and this response to a change in salinity contributed to the significant interaction between time and treatment (two-way within-subjects ANOVA, F13,18 = 2.60; p = 0.003). The lack of significant difference in oxygen consumption over time with and without salinity acclimation in any of the other treatments may suggest that oxygen consumption of juvenile L. lithognathus may have been influenced by other untested physiological processes in addition to energy required for osmoregulation. In this study, no significant difference in weight gain and specific growth rate was observed between three salinity treatments throughout the 56-day rearing period of experiment 1 or during the 28-day rearing period in experiment 2. Despite these findings, some mortalities were recorded in both growth experiments at 5‰ salinity. Future research should be undertaken to investigate the interdependence of oxygen consumption, behavioural processes and physiological events in juvenile L. ithognathus under various salinities.

Item Type:Thesis (Masters)
Uncontrolled Keywords:Salinity; growth; oxygen consumption; osmoregulation; metabolic response; Lithognathus lithognathus
Subjects:S Agriculture > SH Aquaculture. Fisheries. Angling
Divisions:Faculty > Faculty of Science > Ichthyology & Fisheries Science
Supervisors:Hecht, T. (Prof.) and Kaiser, H. (Prof.)
ID Code:1705
Deposited By: Nicolene Mvinjelwa
Deposited On:22 Jun 2010 10:28
Last Modified:06 Jan 2012 16:21
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