Broodstock conditioning and larval rearing of the marine ornamental white-striped cleaner shrimp, Lysmata amboinensis (de Man, 1888)

Lysmata amboinensis is a protandric simultaneous hermaphrodite (PSH); individuals develop as males (MPs) and then change to simultaneous hermaphrodites (SHs). PSHs exhibit functions of both males and females during each reproductive cycle. There are a number of important physiological reproductive features that have not been previously studies in this species, including male size at sexual maturity, fecundity of SHs based on body size differences and timing of the sex phase change. To answer the former two questions, MPs were paired with SHs to produce various size combinations. It was found that L. amboinensis MPs were sexually mature at a total length (TL) of 34.0 mm and larval production increased with increasing body length, with large SHs displaying 3 times the larval output of small and medium -sized SHs. To answer the latter question, MPs were exposed to different social situations by being paired with either another MP (of similar or larger size) or with an SH. Indeed, the timing of sex phase change was influenced by the social condition, indicating "environmental sex determination" (ESD). The "default" size at change was 37.1 mm (TL) when MPs were reared alone; when MPs were paired with a larger MP it was the larger MP that changed first to SH, while the partner shrimp changed at a larger size than the "default". If MPs were paired with similar-sized MPs or with SHs, phase change occurred at a smaller size than the "default". The observed patterns are discussed in terms of reproductive opportunities for a species occuring in small groups in the wild, referred to as a "low density" spp. Aquaculture production of L. amboinensis has been problematic due to the prolonged duration of larval development, punctuated by periods of high mortality. Broodstock maturation diets have been shown to affect fecundity and offspring quality. The primary aim of this component of the study was to identify a suitable maturation diet for L. amboinensis from a range of commonly available feeds. The six diets were squid, mussel, adult Artemia, a commercial feed, and combinations of the aforementioned and were fed to L. amboinensis over four reproductive cycles. Broodstock fed the squid-mussel diet lost > ½ of the egg mass during incubation, with decreased larval production, the lowest being 22 larvae. By contrast, broodstock fed adult Artemia retained > 80 % of their eggs; however, hatchability was poor, resulting in low numbers per hatch, ranging from 12 to 51 larvae. The commercial feed yielded high fecundity and larval output. In L. amboinensis, a maturation diet consisting of natural feeds alone results in poor reproductive performance; partial, or complete, replacement with an artificial feed is economically feasible. Lipid enrichment of Artemia to boost their highly unsaturated fatty acid (HUFA) content is a standard procedure to improve diet performance and can be taylored to deliver key nutrients to culture animals. Frozen, lipid enriched adult Artemia were fed to L. amboinensis broodstock to investigate their suitability and elucidate the role of essential fatty acids (EFAs) in enhancing reproductive performance. Four lipid enrichment levels, un-enriched ("unenr"), 1/3 enriched ("1/3 enr"), 2/3 enriched ("2/3 enr") and enriched ("enr") Artemia, were fed to L. amboinensis over three reproductive cycles. Spawning was high for all diets. Viable fecundity (meaning the number of viable larvae produced) varied, however, and was significantly greater for broodstock fed the "enr" Artemia, with a mean 529 (± 77) larvae, as opposed to 49 (± 11) recorded for the "unenr". The increased larval production was attributed to better embryo hatchability and was associated with an increase in the docosahexaenoic (DHA) content of the diet (11% of total fatty acids FAs). The roles of other dietary EFAs are also discussed. The best feeding regime for the larvae in order to achieve high growth, survival and metamorphosis rates in culture and, eventually, production of new stock was also considered of prime importance. Therefore, larval prey items of varying shape, size and dietary value (specifically, rotifers, Artemia nauplii and Artemia metanauplii), and in different concentrations, were examined. Larval growth was not affected by any of the independent variables. Larval survival was influenced by absolute food availability rather than food concentration, given that feeding the early larvae 1 Artemia ml⁻¹, 3 Artemia ml⁻¹, 18 rotifers ml⁻¹ or 54 rotifers ml⁻¹ resulted in no difference. All prey types tested were suitable first feeds for zoea 1 (Z1) L. amboinensis, with survival > 90%, verifying the plasticity of Lysmata spp. However, from Z2 onwards Artemia may be a better feeding option than rotifers, since carry-over effects of the diet to the next larval stage were noted. The nutritional value of the prey affects development of L. amboinensis larvae, with those fed Artemia metanauplii enriched with Algamac-3000 showing high developmental rate and low zoeal stage dispersion. Exposing the larvae to starvation (as control for true diet effects), revealed that L. amboinensis larvae are facultative primary lecithotrophs (FPL), meaning they can moult to Z2 using only endogenous reserves. Triplicate samples of the hepatopancreas, ovaries and tail muscle of L. amboinensis broodstock, and of newly hatched larvae and larvae subjected to a period of starvation or feeding (from hatch to Z2), were processed to generate their total lipid content and FA profiles. The hepatopancreas had a high lipid content, confirming its role as a process and storage organ in L. amboinensis. Lipids were also a major component of ovarian dry weight (dw), in agreement with reports on other crustaceans during maturation. The tail muscle, being a functional rather than a storage organ, contained low total lipids, and was the tissue that closely resembled the FA profile of the newly hatched larvae. Saturated fatty acids (SFAs) and HUFAs were the most abundant components of the lipid profile in broodstock tissues and in larvae. Monounsaturated fatty acids (MUFAs) may have been preferentially catabolized to meet energetic and metabolic requirements. It appeared polyunsaturated fatty acid (PUFA) and HUFA requirements were met through the larval diet. DHA and eicosapentaenoic (EPA) were preferentially retained during nutritional stress, confirming their importance for L. amboinensis during early larval development. Mouthparts and alimentary canal were examined in L. amboinensis larvae using scanning electron microscopy and histology. The morphology of mouthparts and digestive tract structures at different larval stages, indicate that ingestive and digestive capabilities are well developed in the species from early on. With increasing age of the larvae, the mouthpart appendages increased in size, the hepatopancreas in tubular density and the midgut in length. The density of setae, and robustness of teeth and spines of individual structures, increased. The most pronounced changes, from early to late stage larvae, involved the formation of pores on the paragnaths and labrum, the transformation of the mandibular spine-like teeth to molar cusps, the development of the filter press in the proventriculus, and of infoldings in the previously straight hindgut. The results suggest that early stage L. amboinensis larvae may benefit from soft, perhaps gelatinous prey, whereas later stages are better equipped to handle large, muscular or fibrous, foods