Fresh or formulated: a preliminary evaluation of fresh blue mussel (Mytilus galloprovincialis) and formulated experimental feeds with inclusion of fresh blue mussel on the growth performance of hatchery-reared juvenile slipper lobster (Thenus australiensis)

Following recent advances in hatchery technology and large-scale larval rearing of spiny and slipper lobsters, a greater understanding of key nutritional requirements is now imperative to facilitate feed development for juvenile culture. However, there is a lack of relevant information available for the slipper lobsters, particularly Thenus species. This study sought to evaluate the potential requirements for and effects of a fresh ingredient component in a formulated feed on the growth performance of hatchery-reared juvenile Thenus australiensis. This was assessed using six formulated experimental feeds incorporating fresh blue mussel flesh (BM; Mytilus galloprovincialis) in a geometric series (0, 1.6, 3.1, 6.3, 12.5 and 25.0% dry matter) administered continuously over 9 weeks. An additional dietary treatment of blue mussel half shells (BMHS) was included as a reference feed to establish a benchmark of growth potential. Survival and moult frequency were unaffected by feed treatment. Lobsters fed BMHS displayed a clustered or synchronised moulting pattern with two major moulting events lasting several days each during the experiment. In contrast, lobsters provided experimental feeds moulted continuously throughout the experiment. The BMHS produced approximately 2-fold greater growth compared to experimental feeds, while BM incorporated into experimental feeds had no beneficial effect on growth at any inclusion level. Growth mirrored feed intake where it was also found that feed intake on a dry matter basis was approximately 2-fold higher for BMHS compared to experimental feeds, while biological feed conversion ratios were similar for all feeds. Thus, dry matter intake appeared to be primarily responsible for the difference in growth rates achieved. Bulk chemical analysis revealed that BMHS-fed lobsters had significantly lower ash content coupled with higher gross energy, total lipid and polar lipid contents on a proportional basis compared to lobsters fed formulated experimental feeds. Lobster haemolymph Brix values were also significantly higher in the BMHS treatment lobsters. Higher Brix coupled with decreasing feed intake suggests these lobsters were on average at a more advanced stage within the moult cycle and offers a possible explanation for differences in body chemistry. In conclusion, while growth rates were lower in animals fed formulated feeds compared to benchmark growth performance, overall survival, moulting and growth performance revealed the potential of the basal experimental feed formulation as a reference for future nutrition research with this species without a requirement for inclusion of fresh BM. The research highlights that significant opportunities exist to improve slipper lobster growth performance through maximising feed intake.