page_title: Caprella mutica
section_title: Reproduction and life history
hierarchical_section_title: Caprella mutica / Ecology and biology / Reproduction and life history
caption_attribution_description: English: Gnathopod anatomy of Caprella mutica (Amphipoda: Caprellidae)
context_page_description: Caprella mutica, commonly known as the Japanese skeleton shrimp, is a species of skeleton shrimp. They are relatively large caprellids, reaching a maximum length of 50 mm. They are sexually dimorphic, with the males usually being much larger than the females. They are characterized by their "hairy" first and second thoracic segments and the rows of spines on their bodies. Body color ranges from green to red to blue, depending on the environment. They are omnivorous highly adaptable opportunistic feeders. In turn, they provide a valuable food source for fish, crabs, and other larger predators. They are usually found in dense colonies attached to submerged man-made structures, floating seaweed, and other organisms.
  C. mutica are native to shallow protected bodies of water in the Sea of Japan. In as little as 40 years, they have become an invasive species in the North Atlantic, North Pacific, and along the coasts of New Zealand. They are believed to have been accidentally introduced to these areas through the global maritime traffic and aquaculture.
context_section_description: Wild populations of Caprella mutica show a higher number of females than males. This may be related to the fact that females are aggressively defended by males from competing males, resulting in high male mortality. The larger sizes and greater visibility of males also make them more vulnerable targets for predators that rely on eyesight like fish. C. mutica are r-strategists. They reproduce all throughout the year, with peak seasons in the summer (March to July).
  Males exhibit sexual competition and courting behavior. They aggressively engage in "boxing matches" using their large second pair of gnathopods in the presence of receptive females. These encounters often have lethal results, as the gnathopods and their poison teeth can be used to impale or slice an opponent in half. Males will also repeatedly touch the exoskeletons of the females with their antennae to detect signs of moulting (ecdysis). Like all crustaceans, females are only capable of mating shortly after shedding their old hardened exoskeletons.
  Amplexus lasts for 10 to 15 minutes. Once mated, the males will defend the females for a short period (around 15 minutes). After this period, the females begin to exhibit aggressive behavior and will drive off the males. They will then bend their fourth and fifth pereonites at a 90-degree angle. Once their genital openings (located on the fifth pereonite) are aligned with the opening of the brood pouches, they quickly deposit fertilized eggs into them. Females carrying fertilized eggs remain highly aggressive towards males throughout the brooding period, indicating maternal behavior intended to protect the developing embryo from male aggression.
  A brood pouch of a female can contain 3 to 363 eggs, averaging at 74 eggs. Larger females tend to produce more eggs. The eggs are incubated inside the brood pouch for 30 to 40 days before hatching. Like all amphipods, caprellids lack a planktonic larval stage and the hatchlings resemble miniature adults. The juveniles may cling to their mothers upon hatching and the females continue to protect their offspring that remain close. Hatchlings measure around 1.3 to 1.8 mm (0.051 to 0.071 in) and grow to an average of 0.4 to 0.9 mm (0.016 to 0.035 in) per instar.
  C. mutica mature rapidly, moulting at an average of once each week until they enter the "premature stage", becoming sexually differentiated at the fifth instar. The durations between moulting cycles then become longer in their seventh to ninth instars, averaging at once every two weeks until sexual maturity. This can occur in as early as 21 days and not later than 46 days after hatching, depending on environmental conditions. In wild populations, however, this can take as much as six months when the juveniles are hatched in the late summer.
  Males begin to increase in size at a faster rate with each successive moult after the seventh instar. Females, on the other hand, produce their first brood at the seventh instar. They may moult several times as adults, becoming sexually receptive each time until death. The average lifespan of C. mutica in laboratory conditions is 68.8 days for males and 82 days for females.
caption: The gnathopods of Caprella mutica males are used in aggressive "boxing matches" that can often be lethal.[28]
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