Growth rates and survival of western rock lobster (Panulirus cygnus) at two temperatures (ambient and 23 °C) and two feeding frequencies

Wild caught post-pueruli, year one and year two post settlement juvenile western rock lobster, Panulirus cygnus, were held at ambient temperatures (15.6 degrees C to 23.1 degrees C; mean 19.0 +/- 0.07 degrees C) or at 23 degrees C, and fed the same ration of a formulated pellet diet either once per night, or 3 times per night, over 12 months, to determine whether elevated temperatures and multiple feeds per night would stimulate growth through increased metabolism and feed utilisation without significant negative impacts on survival. Survival of post-pueruli (mean 63%) did not differ between ambient and 23 C. Survival of year 1 and 2 juveniles was higher at ambient temperatures (p<0.01 ambient: year 1 juveniles, 68%; year 2 juveniles, 88%; 23 degrees C: 57% and 74%, respectively). Feeding frequency did not affect survival of post-pueruli and year 2 juveniles (mean 63%, 81% respectively), but survival was 9% higher for year 1 juveniles fed three times per night (58% versus 67%; p<0.01). All lobsters grew faster at 23 degrees C than at ambient temperatures (p<0.05), with the growth of post-pueruli almost doubled at 23 degrees C (weight gain at 23 degrees C versus ambient: post-pueruli, 18 438 % versus 9 915 %; year 1 juveniles 259% versus 165%; year 2 juveniles 23% versus 21%). Feed frequency did not influence the growth of year 1 and 2 juveniles. However, there was an interaction effect of temperature and feed frequency on post-pueruli where weight and carapace length were significantly higher at ambient temperatures when post-pueruli were fed three times a day, whereas at 23 degrees C weight and carapace length were significantly greater when fed once per day (p<0.05). Feed intake (g pellet dry matter lobster(-1) day(-1)) of pellet was higher at 23 degrees C for all lobsters (p<0.05), but was the same between lobsters fed 3 times per night versus once per night. This study has shown that increasing temperatures to 23 degrees C significantly improved the growth of P. cygnus post-pueruli without any adverse effects on survival. The faster growth rates exhibited by year 1 and 2 juveniles at 23 degrees C may potentially offset their lower survival by significantly reducing culture period. There is no benefit of feeding P cygnus multiple times at night in terms of growth and survival. The implications for P. cygnus culture are that temperatures should be maintained close to 23 degrees C during the entire growout period, with due care taken to minimise mortalities through adequate provision of food and shelter. Feeding P cygnus once daily to excess just prior to dusk to co-incide with nocturnal feeding behaviour is recommended. (C) 2008 Elsevier B.V. All rights reserved.