The inclusion in feed formulations of ingredients that act as attractants and feeding incitants or stimulants has been proposed as a means of increasing feed consumption, and hence growth, of farmed shrimp. Squid, crustacean and krill meals, fish and krill hydrolysates and a betaine product (Finnstim) were examined to assess their relative effectiveness in increasing the feed intake of black tiger shrimp Penaeus monodon. These presumed feeding effectors were added to a base feed at between 5 and 50 g kg−1. Given a choice between the base feed and one containing one of the test ingredients, P. monodon showed a significantly greater preference for the feeds containing crustacean or krill meal. Four of the presumed feeding effectors were further evaluated in a growth response experiment. There was no significant difference in the amount the shrimp consumed of any of the feeds. However, the growth rate of the shrimp was about 20% faster on the feeds containing crustacean meal or krill meal. Although ingredients such as crustacean meal or krill meal can improve feed intake, in practical feed formulations that contain significant amounts of terrestrial protein but relatively low levels of marine ingredients, there does not appear to be need for additional feeding effectors. However, crustacean meal and krill meal do provide a significant nutritional benefit, as seen by the improved growth rates in this study.

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The fast-growing tropical lobster Panulirus ornatus is a good aquaculture candidate generating increased research to develop potential feeds. We conducted a 12-week experiment, assessing growth, survival and tissue carotenoid levels of juvenile P. ornatus. Lobsters were fed either pelleted feeds supplemented with astaxanthin and containing 30, 60, 90 or 120 mg total carotenoid kg )1 ; or one of two fresh mussel reference feeds -blue Mytilus edulis and green-lipped Perna canaliculus. There was no clear dose response, in terms of growth rate, to increasing dietary astaxanthin content; mussel-fed lobsters had inferior growth rates. Twelve-week survival was unaffected by treatment. Whole lobster carotenoid (4.7, 16.7, 27.8 and 32.8 mg kg )1 , dry matter basis) increased with increasing dietary astaxanthin; pre-treatment carotenoid was 22.2 mg kg )1 . Apparent total carotenoid content of the mussel-fed lobsters was unexpectedly high because of interference by other pigments. High-performance liquid chromatographic analysis of free astaxanthin levels varied from a pre-treatment value of 7.3 mg kg )1 to 2.0, 7.6, 12.5 and 23.6 mg kg )1 with increasing dietary astaxanthin, and 3.5 (green-lip) and 5.9 (blue) mg kg )1 for the mussel-fed lobsters. Although dietary astaxanthin, over the investigated range, did not affect growth rate or survival, there was a dose-response increase in tissue carotenoid content and darkening of the exoskeleton pigmentation, which may have important implications for immunocompetency and marketing. These implications are discussed in the context of pelleted feed development for this species. KEY WORDS

Critical to the development of a cost‐effective feed for the tropical spiny lobster Panulirus ornatus is knowledge of its response to the protein and lipid (or energy) content of the feed. An experiment of 12 weeks duration was carried out to examine growth responses of juvenile lobsters to pelleted diets that provided six crude protein (CP) levels [320–600 g kg−1 dry matter (DM)] and two lipid levels (nominally 60 and 100 g kg−1 DM). Lobsters (mean initial weight of 1.8 g) were held in groups of nine or 10 animals in 24 × 350 L tanks, fed twice daily at a restricted level, and maintained at 28 °C. Maximal growth responses occurred at dietary CP contents of 474 g kg−1 for the 60 g kg−1 lipid series and 533 g kg−1 for the 100 g kg−1 lipid series. A second experiment, of 4 weeks duration, compared two dietary treatments: a mixture of two of the best diets from the first experiment, and a commercial shrimp (Penaeus japonicus) feed. Lobsters were held under the same experimental conditions as in the first experiment, but were fed to excess twice daily. Their growth was significantly greater (P < 0.05) on the shrimp feed (0.68 g week−1) than on the laboratory‐pelleted diets used in the main study (0.32 g week−1). The results indicate that the optimal dietary protein and lipid content of the diet for P. ornatus is about 530 and 100 g kg−1, respectively.

The reproductive performance of domesticated Penaeus monodon was assessed when fed on two experimental semi‐moist maturation diets varying in their arachidonic acid content for 21 days before ablation and throughout a 17‐day reproductive assessment. The biochemical composition of the two semi‐moist two diets was similar with the exception of arachidonic acid (ARA) content; the basal diet (BAS) consisting of 0.9 g kg−1 DM ARA (1.1% of total fatty acids) and the supplemented diet (ARA‐SUP) consisting of 5.0 g kg−1 DM ARA (5.8% of total fatty acids). ARA/EPA and ARA/DPA ratios were 0.1 in the BAS diet and 0.5 in the ARA‐SUP diet. Fatty acid composition of the spawned eggs was comparable between diets with the exception of ARA concentration, which was higher in the ARA‐SUP (8.95 ± 0.44 g kg−1 DM) than the BAS (3.23 ± 0.17 g kg−1 DM) (P < 0.0001). The cumulative percentage of females spawning (mean ± SE after 17 days) (31.9 ± 7.0%; 24.1 ± 1.3%), number of spawnings per female (0.48 ± 0.1; 0.29 ± 0.02), and eggs per female (62 520 ± 16 935; 44 521 ± 9914) was significantly (P < 0.0001) higher for the ARA‐SUP than the BAS. Results of this study suggest that arachidonic acid plays a key role in promoting egg development and spawning in P. monodon.