There is a growing interest in preserving microalgal preparations to maintain constant properties over a long period. The aim is to ensure sufficient delivery of essential fatty acids (and other key nutrients) to mollusc and crustacean larvae and to zooplankton used as live prey in the first feeding of fish larvae. For example, the rotifer Brachionus plicatilis has to be enriched with polyunsaturated fatty acids (PUFA) prior to fish feeding. We used four microalgal species [Isochrysis galbana (T-ISO), Chaetoceros muelleri (CHGRA), Pavlova lutheri (MONO), and Nannochloropsis sp.] both as fresh culture or in a frozenconcentrated form to enrich rotifers. Overall, rotifers had similar relative fatty acid levels when fed the frozen-concentrated or fresh microalgal diets. The levels of 20:4n-6, 22:6n-3, and 20:5n-3 between B. plicatilis and the microalgal diets were linearly correlated. The fatty acid 20:4n-6 was the most readily assimilated: the content found in rotifers reached half the level measured in the microalgal diets. Our results indicate that both the fresh and frozen-concentrated forms of the four microalgal species can be used to enrich PUFA levels in rotifers. Further experiments should be conducted to test if assimilation differs when rotifers are enriched with mono-or multispecific microalgal preparations. KEY WORDS

The proliferation of bacteria in intensive aquaculture systems may be responsible for poor growth and mass mortality of marine fish larvae. Essential fatty acids provided in the diet could protect larvae by modulation of the immune response via arachidonic acid (AA) and eicosapentaenoic acid (EPA). Winter flounder Pseudopleuronectes americanus larvae were fed rotifers Brachionus plicatilis enriched with three commercial diets containing different fatty acid profiles. Bacterial colonization on the gills and skin and in the intestinal lumen was evaluated at the end of the rotifer feeding period (day 26), and growth was surveyed until metamorphosis. At 26 days post hatching, larvae fed rotifers containing the higher AA content and with a higher docosahexaenoic acid (DHA) to EPA ratio showed better growth and the lowest bacterial colonization of the intestinal lumen compared to larvae fed rotifers with the lowest AA and DHA : EPA levels. AA had been selectively incorporated into the polar lipids of larvae fed the rotifers enriched with the three diets. This is the first study in winter flounder larvae to report a link between different commercial rotifer enrichments and bacterial density in intestinal lumen.

The nematode Panagrolaimus sp. was tested as live feed to replace Artemia nauplii during first larval stages of whiteleg shrimp Litopenaeus vannamei. In Trial 1, shrimp larvae were fed one of four diets from Zoea 2 to Postlarva 1 (PL1): (A) Artemia nauplii, control treatment; (NC) nematodes enriched in docosahexaenoic acid (DHA) provided by the dinoflagellate Crypthecodinium cohnii; (N) non-enriched nematodes; and (Algae) a mixture of microalgae supplemented in C. cohnii cells. In Trial 2, shrimp were fed (A), (NC) and a different treatment (NS) with nematodes enriched in polyunsaturated fatty acids (PUFAs) provided by the commercial product S.presso ® , until Postlarva 6 (PL6). Mysis 1 larvae fed nematodes of the three dietary treatments were 300 μm longer (3.2 ± 0.3 mm) than control larvae. At PL1, control shrimp were 300 μm longer (4.5 ± 0.3 mm) than those fed DHA-enriched or PUFAs-enriched nematodes. No differences were observed in length and survival at PL6 between control larvae and those fed DHA-enriched nematodes (5.1 ± 0.5 mm; 33.1%-44.4%). Shrimp fed microalgae showed a delay in development at PL1. This work is the first demonstration of Panagrolaimus sp. suitability as a complete substitute for Artemia in rearing shrimp from Zoea 2 to PL6. K E Y W O R D S Crypthecodinium cohnii, docosahexaenoic acid enrichment, Litopenaeus vannamei, nematode, Panagrolaimus sp., shrimp feeding How to cite this article: Seychelles LH, Happe S, Palacios E, et al. Successful rearing of whiteleg shrimp Litopenaeus vannamei larvae fed a desiccation-tolerant nematode to replace Artemia. Aquacult Nutr. 2018;24:903-910. https://doi.

Rotifers (Brachionus plicatilis), commonly used at first feeding in commercial fish hatcheries, carry a large bacteria load. Because they are relatively poor in essential fatty acids, it is common practice to enrich them with fatty acids, including arachidonic acid (AA). This study aims to determine whether prey enrichment with AA may act as a prebiotic and modify the microbial community composition either in AA-enriched rotifer cultures or in larval-rearing water using winter flounder (Pseudopleuronectes americanus) as a larval fish model. AA enrichment modified the bacterial community composition in both the rotifer culture tanks and the larval-rearing tanks. We observed an increase in the number of cultivable bacteria on TCBS (thiosulfate-citrate-bile salts-sucrose) agar, used as a proxy for the abundance of Vibrio sp. The results suggest that AA may also play an indirect role in larval health.

Life cycle analysis data of the free-living, bacterial-feeding Panagrolaimus sp. strain NFS 24-5 were assessed at different temperatures using a hanging drop method with single male and female individuals and a food density of 3 x 10^ Escherichia coli cells ml"'. Lifespan at the moment when the first egg was laid was 5.7 days at 21°C and 4 days at 25, 27 and 29°C. The intrinsic rate of natural increase (rm) was 0.53 at 2rC, 0.81 at 25°C, 0.93 at 27°C and 0.81 at 29°C, corresponding to population doubling times (PDT = \n2/rm) of 1.3, 0.9, 0.7 and 0.9 days, respectively. Over 200 offspring per female were produced at 27°C. All other temperatures yielded fewer offspring. When females were kept without males, the life span was 49 days, whereas the last reproductive female (banging drop with male individual) died after 16.5 days. These data will contribute to the interpretation of nematode population dynamics recorded in liquid eulture.Keywords -aquaculture, fecundity, generation time, intrinsic rate of natural increase, life history trait analysis, lifespan, offspring production, population doubling time.As catches of marine fish have decreased during the past decades, aquaculture production is gaining importance. Future production of crustaceans and fish species depends on increasing demands for high quality food. During the early stages of development, marine crustacean and fish larvae rely on iive food. Feeding of iarvai stages of the brine shrimp Artemia is standard feed for crustacean larvae all over the worid. However, natural resources are limited (Focken et al, 2006). A possible alternative to Artemia are free-living, bacterial-feeding nematodes (Rhabditida). Biedenbach et al (1989) used Panagrellus redivivus L. with aigae as a larvai diet for the white shrimp Litopenaeus vannamei Boone and found significantly better results compared to the typical Artemia diet. However, this nematode cannot be desiccated. Therefore, Honnens & Ehiers (2013) proposed to use the free-living nematode Panagrolaimus sp. (strain NFS 24-5) as a potential food organism as it can easily survive desiccation and thus facilitate the development of a product formulation that is stable during stor-, but precise knowledge on the biology of this nematode is scarce. A cost-efficient production process demands maximum yields and short process time (Ehlers, 2001;Hirao & Ehlers, 2009). Optimum temperature is an important factor for improving a mass production process. Knowledge on iife history traits and growth parameters of a nematode can possibly improve the mass production process. Life cycle analysis data provides detailed information to understand the biological approach of a nematode species, i.e., the nematode's age at sexuai maturity, iifespan, net reproductive rate, totai fertiiity rate, generation time, intrinsic rate of natural increase, population doubling time and somatic growth rate. This study analysed the life cycle of the free-iiving, bacterial-feeding Panagrolaimus sp. strain NFS 24-5 at different temperatures by a recently ...