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

Abstract

Wild caught post-pueruli, year one and year two post settlement juvenile western rock lobster, Panuliruscygnus, were held at ambient temperatures (15.6 C to 23.1 C; mean 19.00.07 C) or at 23 C, and fed thesame ration of a formulated pellet diet either once per night, or 3 times per night, over 12 months, todetermine whether elevated temperatures and multiple feeds per night would stimulate growth throughincreased metabolism and feed utilisation without significant negative impacts on survival. Survival of postpueruli(mean 63%) did not differ between ambient and 23 C. Survival of year 1 and 2 juveniles was higher atambient temperatures (pb0.01 ambient: year 1 juveniles, 68%; year 2 juveniles, 88%; 23 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%;pb0.01). All lobsters grew faster at 23 C than at ambient temperatures (pb0.05), with the growth ofpost-pueruli almost doubled at 23 C (weight gain at 23 C versus ambient: post-pueruli, 18 438 % versus 9915 %; year 1 juveniles 259% versus 165%; year 2 juveniles 23% versus 21%). Feed frequency did not influencethe growth of year 1 and 2 juveniles. However, there was an interaction effect of temperature and feedfrequency on post-pueruli where weight and carapace length were significantly higher at ambienttemperatures when post-pueruli were fed three times a day, whereas at 23 C weight and carapace lengthwere significantly greater when fed once per day (pb0.05). Feed intake (g pellet dry matter lobster-1 day-1)of pellet was higher at 23 C for all lobsters (pb0.05), but was the same between lobsters fed 3 times pernight versus once per night. This study has shown that increasing temperatures to 23 C significantlyimproved the growth of P. cygnus post-pueruli without any adverse effects on survival. The faster growthrates exhibited by year 1 and 2 juveniles at 23 C may potentially offset their lower survival by significantlyreducing culture period. There is no benefit of feeding P. cygnus multiple times at night in terms of growthand survival. The implications for P. cygnus culture are that temperatures should be maintained close to 23 Cduring the entire growout period, with due care taken to minimise mortalities through adequate provision offood and shelter. Feeding P. cygnus once daily to excess just prior to dusk to co-incide with nocturnal feedingbehaviour is recommended.