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Studies on social control of functional sex in crustaceans are scarce and focused on hermaphroditic species. Hence, the objective of this study was to determine whether adult sex ratio affects juvenile sexual differentiation in a gonochoristic caridean shrimp, Neocaridina davidi (Bouvier 1904). We tested two alternative hypotheses: (1) that undifferentiated juveniles become males when reared in the presence of adult females and vice versa; and (2) that the presence of adult males affects juvenile sexual differentiation through androgenic gland secretions. Newly hatched juveniles were maintained with adult males or adult females during a 50-day period, after which they were sexed. In both treatments, juvenile sex ratios showed no deviations from the expected 1:1 relationship. This suggests that adult sex ratio is not a selective force determining juvenile phenotypic sex, even though mating opportunities may be null for juveniles differentiating into the sex of surrounding adults. The 1:1 sex ratio observed in broods reared with adult males and adult females also suggests that the potential chemical cues released by adults have neither masculinizing nor feminizing effects on undifferentiated juveniles. Present results reject our initial hypotheses and are consistent with a strong genetic basis of juvenile sexual differentiation in caridean shrimps. Les études sur le contrôle qu’exerce l’environnement social sur le sexe fonctionnel chez les crustacés sont rares et portent sur des espèces hermaphrodites. L’objectif de la présente étude consistait donc à déterminer si le rapport de masculinité des adultes a une incidence sur la différenciation sexuelle des juvéniles chez la crevette cerise (Neocaridina davidi (Bouvier, 1904)) (Decapoda, Caridea) gonochoriste. Nous avons testé les deux hypothèses suivantes : (1) les juvéniles non différenciés deviennent des mâles quand ils sont élevés en présence de femelles adultes et vice versa; (2) la présence de mâles adultes influence la différenciation sexuelle des juvéniles par l’entremise de sécrétions des glandes androgènes. Des juvéniles nouvellement éclos ont été maintenus en présence de mâles adultes ou de femelles adultes pendant 50 jours, après quoi leur sexe a été déterminé. Pour les deux traitements, les rapports de masculinité ne présentaient aucun écart par rapport à la relation de 1:1 attendue. Cela porte à croire que le rapport de masculinité des adultes n’est pas une force de sélection déterminante du sexe phénotypique des juvéniles, même si les occasions d’accouplement peuvent être inexistantes pour les juvéniles qui prennent le sexe des adultes qui les entourent. Le rapport de masculinité de 1:1 observé pour les pontes élevées en présence de mâles adultes ou de femelles adultes donne aussi à penser que d’éventuels signaux chimiques émis par les adultes n’ont pas d’effet masculinisant ni féminisant sur les juvéniles non différenciés. Les résultats de l’étude infirment nos hypothèses initiales et concordent avec l’interprétation d’une forte base génétique de la différenciation sexuelle des juvéniles chez les crevettes caridines. Fil: Tropea, Carolina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Biodiversidad y Biología Experimental y Aplicada. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biodiversidad y Biología Experimental y Aplicada; Argentina Fil: López Greco, Laura Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Biodiversidad y Biología Experimental y Aplicada. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biodiversidad y Biología Experimental y Aplicada; Argentina

This study aims to analyze the functional anatomy of the male reproductive system in Neocaridina davidi, a very popular ornamental species of caridean shrimp. Mature males were cold-anaesthetized and their reproductive systems were dissected for histological and histochemical analysis, while the spermatozoa and spermatophore wall ultrastructure were analyzed under transmission electron microscopy. The male reproductive system consisted of two coiled testes, which were continuous with the vasa deferentia. Testes were positioned on the dorsal side of the cephalothorax above the hepatopancreas, and comprised seminiferous tubules where spermatogenesis occurred. Each vas deferens (VD) was a long tube dorsolaterally positioned with respect to the hepatopancreas, and increased in diameter at the distal end. Three regions could be recognized in the VD: proximal, middle, and distal. The proximal region had a cylindrical epithelium with secretory cells. The middle region (or typhlosole) had a dorsal fold (or typhlosole) with a thick columnar epithelium and high secretory activity. The spermatophore was a continuous cord with three acellular layers, which were mainly characterized by the presence of neutral glycoconjugates and proteins. The sperm morphology was distinct from the inverted cup-shaped spermatozoa observed in the majority of caridean shrimps. The spermatozoa in specimens of N. davidi were spherical in shape, with a cross-striated, single, short spike, and arranged in clusters of three or four sperm cells. The composition of the spermatophore, and the arrangement and form of the spermatozoa, seem to be unique in comparison to other species of Caridea. © 2019, The American Microscopical Society, Inc.

The relationship between parental mass and female reproductive output, as well as offspring quality, was studied in the red cherry shrimp (Neocaridina davidi (Bouvier, 1904)) under controlled laboratory conditions. Adult males and females of the same age were paired combining different shrimp masses. The number of hatched juveniles from large females was higher than that from small ones, but no influence of paternal mass was detected on this variable. Both the mass of newly hatched juveniles and their growth increment during a 60-day period were similar for all parental masses. Shrimps reached sexual maturity at the end of the growth period in all treatments, and their biochemical reserves (glycogen, lipid, and protein concentrations) were not associated with maternal and paternal masses. However, lipid concentration was higher in female offspring than in male offspring. The present results show that, unlike maternal mass, paternal mass had no effect on female reproductive output and offspring quality, suggesting that the contribution of males to offspring development was adequate regardless of male size.

This study was conducted to evaluate dietary inclusion effects of Arthrospira (Spirulina) platensis (SP) meal on the growth, survival, biochemical composition, and particularly reproductive performance during eight successive spawning events in the caridean red cherry shrimp, Neocaridina davidi, for 11 months. Juveniles were fed with six diets containing 0 (control), 1, 3, 5, 8, and 10% of SP levels. Most growth indicators in terms of final weight, specific growth rate, and average daily growth rate were significantly higher in the shrimp fed with SP10. The highest survival of females (75–81%) was recorded in shrimp fed SP8–10, being different from the other groups (25–73%). No changes were observed in lipid and moisture contents, and protein content showed an increasing trend with dietary Spirulina levels up to 10%. Absolute fecundity (eggs per female) was significantly affected in order of the highest to lowest viz. 45, 39, 30, 28, 27, and 24 with different incorporations. The relative fecundity (eggs per female’s body weight) of shrimp fed SP8–10 showed differences with the other groups. Except for the control, all Spirulina-fed females of SP1–5 showed hatching percentages of 78–84% compared with those of 91–94% for SP8–10. Relative fecundity in females fed SP8–10 showed differences from the fourth to the sixth spawning events compared with the other groups; this trend decreased non-significantly until the eighth spawning. The results obtained suggest that dietary inclusion of S. platensis meal at a level of 8–10% can improve the growth, survival and, in particular, reproductive performance of red cherry shrimp in commercial aquaria during maturity only up to the sixth spawning event.

Meiofauna serves as a link between microbial production and higher trophic levels, such as macroinvertebrates and juvenile fish. However, the role of meiofauna in the freshwater food web has not been accurately evaluated, and the influence of shrimp predation on freshwater meiofaunal assemblages is unknown. In this study, the predation effects of Neocaridina davidi, an ornamental freshwater shrimp native to inland water bodies in Asia, on meiofaunal density, biomass, structure, and secondary production were examined using model ecosystems (microcosms) that were sampled repeatedly over 42 days. Shrimp predation altered the structure of the meiofaunal community over the course of the experiment, in particular the density, biomass, and secondary production of nematodes, microcrustaceans, and oligochaetes. An analysis of the stomach contents of N. davidi indicated a high degree of omnivory and the frequent consumption of meiofaunal organisms. The results indicated that predation by the freshwater shrimp N. davidi depresses the overall abundance, biomass, and secondary production of meiofaunal assemblages. Moreover, they also provide insights into food-web ecology and the first evidence of freshwater shrimp predation on meiofaunal assemblages. (C) 2016 Elsevier GmbH. All rights reserved.

The ‘Red Cherry shrimp’, Neocaridina davidi is a small freshwater caridean shrimp living, originally, in various kinds of inland water bodies around Asian countries. This shrimp has reached several countries for ornamental use; however, basic information on the biology of the species is still scarce in the literature. Its early post embryonic development morphology has not yet been described. This paper focused on the production and the development of early post-hatching stages of N. davidi, its male secondary sexual features, observation of the gonads and the presence of females with embryos. The larval development of N. davidi was almost suppressed as noted by the presence of relatively large-sized eggs, first stage hatching as a decapodid; and the tail fans were present only from the 2nd post-hatching stage. A biological important consequence of the presence of this Red Cherry shrimp species in the Neotropics is its potential release into nature, which could cause its rapid dispersion affecting populations of other indigenous caridean freshwater shrimps. Fil: Pantaleão, João A F.. Universidade Estadual Paulista Julio de Mesquita Filho; Brasil Fil: Gregati, Rafael A.. Universidade Estadual Paulista Julio de Mesquita Filho; Brasil. Universidade Estadual do Centro‐Oeste; Brasil Fil: da Costa, Rogério C.. Universidade Estadual Paulista Julio de Mesquita Filho; Brasil Fil: Lopez, Laura Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Biodiversidad y Biología Experimental y Aplicada. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biodiversidad y Biología Experimental y Aplicada; Argentina Fil: Negreiros Fransozo, María Lucía. Universidade Estadual Paulista Julio de Mesquita Filho; Brasil

The effect of density on growth, sex ratio, survival, and biochemical composition of the red cherry shrimp, Neocaridina davidi Bouvier, 1904, was studied to determine optimum rearing conditions in this ornamental species. It was tested whether gender segregation affected growth and survival of the species. To test the effect of density (Experiment 1), hatched juvenile shrimp were kept at three different densities: 2.5, 5, and 10 individuals l-1 (D2.5, D5 and D10, respectively). To test the effect of gender segregation (Experiment 2), 30-day juveniles were reared in three conditions: culture with only females, culture with only males, and mixed culture (females: males 1:1) at 5 individuals l-1 density. Experiments lasted 90 days, and shrimp were weighted either every 30 days (Experiment 1) or 15 days (Experiment 2). At day 90, females kept at D2.5 weighted 45% more than females stocked at D10 (P < 0.05), whereas females from D5 0.05). Males at D2.5 weighted 29% more than D510 (P < 0.05). Survival was high and unaffected by treatment. Sexual differentiation did not differ among treatments. Females from D2.5 had the lowest lipid and protein content, which would occur if they had a higher spawning. Males from D2.5 had higher content of proteins, probably due to their larger size. Gender segregation had no effect over growth and survival; females grew up to a larger size than males both in monosex and mixed culture. It was shown that given to their non-aggressive behavior, N. davidi is tolerant to a highdensity condition, which makes it feasible as an ornamental species., Instituto de Limnología "Dr. Raul A. Ringuelet"