Metin Kumlu

Effects of temperature and salinity on larval growth, survival and development of Penaeus semisulcatus.

Four temperatures (22°C, 26°C, 30°C and 34°C), and the combined effects of three salinity (25, 30 and 35 ppt) and three temperature (26°C, 30°C and 34°C) levels from protozoea 1 (PZ1) to postlarvae 1 (PL1) stages of Penaeus semisulcatus were studied in two separate experiments. In the first experiment, the PZ1 larvae at the lowest temperature of 22°C showed the highest survival (69%) to PL1 compared to 61% at 26°C, 44% at 30°C and 12% at 34°C. However, 22°C slowed the growth and delayed the larval development by about 2–4 days. Growth rate at 30°C (0.44–0.48 mm day−1) was double of that (0.22–0.25 mm day−1) at 22°C. The results showed that P. semisulcatus is tolerant to low, rather than to high temperatures during the larval development. Hence, a water temperature level of about 30°C is optimal for the larval culture of this species. The second experiment showed that temperature exerted a greater influence than the salinity on the growth and survival during the larval development. The range of temperature in which the larvae showed high survival and growth is relatively narrow as compared to that of salinity. At all salinity levels, survival to PL1 (69–77%) was higher at 26°C as compared to 30°C (44–73%) and 34°C (14–21%). However, daily growth rate at 30°C and 34°C was about 60% higher than at 26°C. Larval development was also 3–4 days faster at 30°C and 34°C. Based on the survival and growth results, the best salinity and temperature combination for the culture of P. semisulcatus was 30 ppt and 30°C.

Off-season maturation and spawning of Penaeus semisulcatus by eyestalk ablation and/or temperature-photoperiod regimes

Abstract In this study, nine different treatments were tested on off-season reproductive performance of Penaeus semisulcatus for 60 days in a recirculating system, in round tanks (1.2-m diameter) situated in a greenhouse. A combination of raised temperature (28 °C) and shortened (10 h) or increased day length (14 h) was not sufficient to induce maturation in unablated females of P. semisulcatus . Unablated females showed no sign of ovarian development at a constant low temperature of 20 °C. Cyclic fluctuation (period of 10 days) of water temperature (20–28 °C) at local winter photoperiod regime (10-h illumination) induced successful maturation and even multiple spawnings within the same moulting period. Natural daylight supplementation (14-h illumination) did not produce any advantage over natural illumination (10 h). Unilateral eyestalk ablation had the most profound effect on the induction of ovarian development and spawning in this species. Even at a temperature of 20 °C, eyestalk-ablated females developed their ovaries up to the 4th stage but with still no spawning. It appears that P. semisulcatus requires not only optimal environmental conditions but also a certain stimulus such as ablation or temperature fluctuation for successful maturation and spawning in captivity during the winter season. Small tank size (1.2 m in diameter) did not inversely affect mating success of P. semisulcatus at the sex ratio of 1:2 male/female and 10 shrimp/m 2 stocking density. The present results have demonstrated that eyestalk ablation or cyclic temperature fluctuation techniques can successfully be applied to obtain off-season spawning from P. semisulcatus broodstock in the sub-tropics.

The effects of salinity and added substrates on growth and survival of Metapenaeus monoceros (Decapoda: Penaeidae) post-larvae

This study was carried out to determine the optimal culture salinity and to investigate the effects of added substrate on growth and survival of Metapenaeus monoceros during its nursery culture in two separate experiments. In Experiment 1, at the end of a 50-day culture period, post-larvae (PLs) reared at 5, 10, 20, 30, 35, 40 and 50 ppt displayed 8, 11, 48, 49, 52, 59 and 36% survivals, respectively. Daily growth rates at salinities above 30 ppt (0.266–0.320 mm day−1) were about 5-fold higher than those obtained at salinities below 10 ppt (0.035–0.056 mm day−1) (P 0.05). Mean wet weights acquired at 30–40 ppt (63–71 mg) were 7–8 times higher than those at 5 and 10 ppt (8.12–9 mg) (P<0.05). A rise in salinity resulted in a drastic increase in biomass (over 50-fold) from 0.018 g at 5 ppt to 0.927 g at 40 ppt. Hence, optimum salinity for the nursery culture of M. monoceros PLs appeared to be between 30 and 40 ppt at 28°C. In experiment 2, Group A received no additional substrate while the other two groups had added substrates consisting of wooden frame with vertical (Group B) or horizontal (Group C) plastic mesh. Additional substrate increased habitable surface area approximately 330%. Percentage survivals in Group A, B and C were 71, 70 and 63%, respectively. TL was significantly lower in Group C (15.65 mm) than in either Group A (17.71 mm) or Group B (17.23 mm) (P<0.05). The PLs in Group A attained a significantly greater mean final weight (62 mg) than those (40–55.14 mg) in both treatments containing artificial substrates. The PLs in Group B and C had 12% and 40% lower biomass than that in Group A. The current results demonstrated that the use of either vertically and horizontally placed substrates do not provide any advantage during the nursery culture of M. monoceros.