Getting ready for mating: The importance of male touching as an accelerator of ovarian growth in a caridean shrimp

Development and testing of a sedation protocol for Neocaridina davidi

Neocaridina davidi, a small freshwater shrimp native to Asia, specifically China, Japan, Korea, and Vietnam, possesses remarkable resistance to poor water quality and offers various advantages over other invertebrate species to examine crucial issues in neuroscience and other related areas. These advantages include robustness, ease of maintenance, and transparency, making them useful for in vivo studies with optical imaging techniques. Despite its suitability for research purposes, particularly in the fields of imaging and fluorescent techniques, the lack of attention given to this species has resulted in the absence of a robust and replicable sedation protocol for immobilization and safe manipulation. Consequently, researchers face challenges in performing experimental procedures while minimizing harm to this specimen. In this study, we have developed and evaluated a simple sedation protocol specifically designed for Neocaridina davidi, assessing its effectiveness using light microscopy and image processing.

Long-Term Exposure of the Red Cherry Shrimp Neocaridina davidi to Diclofenac: Impact on Survival, Growth, and Reproductive Potential

The current study was aimed at studying the long-term effects of diclofenac on the freshwater shrimp Neocaridina davidi, concerning survival, somatic growth, and reproduction. In this study, both ovigerous females and males of this species were exposed for 63 d to 0 (control), 0.1, or 1 mg/L of diclofenac. At the highest concentration, significant mortality was detected, and the somatic growth of females was significantly decreased. The percentage of females with a second spawn, observable from day 45, significantly increased at 1 mg/L, while the time between spawns was significantly reduced at both concentrations assayed. However, the gonadal analysis made at the end of the assay in the surviving females showed a significantly lower proportion of advanced oocytes in females exposed to 1 mg/L, as compared to control. Concerning hatching, the percentage of ovigerous females that could have successful hatching was reduced at 1 mg/L of diclofenac, especially for the first spawn. For the second spawn, the low number of juveniles hatched from females exposed to 1 mg/L also showed a significantly higher incidence of morphological abnormalities, such as hydropsy and underdeveloped appendages. Taken together, these results showed that even when diclofenac was able to produce earlier spawns, the reproductive output of each spawn was reduced.

Effect of social environment on sexual differentiation in the highly gregarious red cherry shrimp (Neocaridina davidi)

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 the gonochoristic red cherry shrimp (Neocaridina davidi (Bouvier, 1904)) (Decapoda, Caridea). We tested two alternative hypotheses: (1) that undifferentiated juveniles become males when reared in the presence of adult females and vice versa; (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.