Growth and longevity of Exosphaeroma hylocoetes (Isopoda) under varying conditions of salinity and temperature

Abstract

The effect of temperature (15 and 25°C) and salinity (15 and 35 practical salinity units) combinations on the growth and longevity of the South African estuarine isopod Exosphaeroma hylocoetes was investigated and data analysed using the logistic growth model. No significant differences (P = 0.43 to 0.54) were obtained for the growth rates of male and female E. hylocoetes under the suite of temperature/salinity combinations. Among the variables considered, temperature was identified as the most important in influencing the growth rates of the isopod. Elevated temperatures promoted faster initial growth in both males and females. Salinity had no significant influence on the growth rates of males and females. Males (25.77 ± 3.40 weeks) lived significantly longer (P < 0.001) than females (21.52 ± 3.00 weeks), allowing males (8.08 ± 0.25 mm mean body length) to attain a significantly larger size than females (6.59 ± 0.25 mm) under experimental conditions. Females, however, attained sexual maturity (at 2.5 mm body length) 2–4 weeks earlier than males (5.5 mm in length). It is suggested that the faster growth rates at the higher temperature/salinity combinations allow the isopod to reach sexual maturity at an earlier stage than those at the lower combinations.

Key words:

• Growth
• Longevity
• Estuarine isopod
• Temperature
• Salinity