罗氏沼虾的特征有哪些，市场上如何分别---This image does not contain any questions, options, mathematical formulas, chemical equations, or tables. It is a photograph. **Image Description:** * **Type:** Photograph of biological specimens. * **Main Elements:** The image displays a collection of multiple large freshwater prawns (likely Giant River Prawns, *Macrobrachium rosenbergii*) resting in a dark-colored container, partially submerged in clear water. * **Prawns:** There are at least five to seven prawns visible, lying in various orientations, with some overlapping. * **Size:** They appear to be of significant size, characteristic of mature prawns. * **Coloration:** Their bodies exhibit a range of colors, from a pale greenish-blue or grey to light brown/orange, particularly on the cephalothorax (head and thorax region). The segmented abdominal sections often show banding of these colors. * **Claws (Chelipeds):** Many prawns feature prominent, elongated claws (chelipeds), which are a striking blue, greenish-blue, or brownish-orange. These claws are typically much longer in males. * **Rostrum and Eyes:** Each prawn has a distinctive rostrum (a spiked projection from the head) and stalked, black compound eyes. * **Antennae:** Numerous long, thin, filamentous antennae, mostly brownish-orange, extend in various directions from the prawns' heads. * **Tail Fan:** The posterior end of the prawns shows a well-defined tail fan, comprising the telson and uropods, which are typically fan-shaped and often retain a greenish or bluish hue. * **Container:** The prawns are held within a dark grey or black container, possibly a plastic tub or basin, which appears to have a slightly rough or worn surface. * **Water:** A shallow layer of clear water is present at the bottom of the container, partially submerging the prawns. Some small air bubbles are visible on the water's surface, particularly in the lower right and left corners. * **Relative Position and Direction:** The prawns are scattered and overlapping, filling most of the frame. Two prominent prawns are visible in the foreground: one in the center with a more golden-brown cephalothorax, and another to its right with a paler, greenish-blue cephalothorax. Their heads are generally pointed towards the top or upper-right of the image. The numerous antennae create a complex network of lines throughout the image. **Image Description:** **Type:** Photograph **Main Elements:** The image depicts a close-up view of a human hand holding three large freshwater prawns (likely giant river prawns or Macrobrachium rosenbergii) within a dark-colored bucket filled with water. Numerous other similar prawns are visible submerged in the water inside the bucket, surrounding the hand. * **Prawns:** * There are at least three large prawns held by the hand, and many more are partially visible in the water, suggesting a significant quantity. * They have elongated, segmented bodies. The overall coloration is a mix of light greenish-blue, greyish, and brownish tones, with some parts of their carapaces and abdomens showing subtle banding or color variations. * Their prominent features include very long, thin antennae (whiskers) extending from their heads, compound eyes (dark, bulbous), and a rostrum (a spiky projection from the head). * Some of the claws (chelipeds) of the prawns, particularly the larger ones, exhibit a distinct bright blue coloration, which is characteristic of male giant river prawns. * The prawns appear fresh and are partially submerged in clear water, suggesting they are alive or freshly harvested. * **Hand:** A human hand, with fingers clearly visible, is holding the three prawns firmly. The hand appears to belong to an adult. Part of a dark, possibly purple or brown, long-sleeved garment (shirt or jacket) is visible on the right side of the image, covering the wrist and lower arm. * **Bucket:** A large, dark-colored (likely black or dark grey) bucket forms the background, containing the water and the prawns. The rim of the bucket is visible in some areas. * **Water:** Clear water fills the bucket, reflecting some light and showing ripples from the movement of the prawns and the hand. The water level appears to be high enough to cover most of the prawns. **Relative Position and Direction:** The human hand is positioned in the lower-middle to right part of the frame, holding the three largest prawns horizontally across the image. The heads of these prawns are generally oriented towards the left. The remaining prawns in the bucket are positioned below and around the hand, in various orientations, some partially submerged. The perspective is looking down into the bucket. **Chart/Diagram Description:** * **Type:** Photograph of live aquatic animals. * **Main Elements:** The image displays a close-up, overhead view of approximately 10-12 large, live freshwater prawns, likely Giant River Prawns (*Macrobrachium rosenbergii*), submerged in a shallow layer of clear water within a dark, possibly black or very dark grey, circular container (such as a bucket or basin). * **Prawns:** * **Count:** Multiple prawns are visible, overlapping and filling most of the container's area. * **Coloration:** Their bodies exhibit a varied coloration, predominantly shades of greenish-grey, blue-grey, and brownish-orange. The cephalothorax (head and thorax region) tends to be darker brown or orange-tinged, while the segmented abdomen is more bluish-green. Some individuals display vibrant blue coloration on their large chelipeds (claws) and walking legs. * **Appendages:** Each prawn possesses a distinct, spiky rostrum extending from its head. Numerous long, slender antennae, typically light brown or translucent, are splayed out in different directions, some extending beyond the visible water surface. Dark, prominent compound eyes are visible on stalks on their heads. Many walking legs are discernible beneath their bodies. The tail fans (telson and uropods) are visible on several prawns, showing a mix of greenish-blue and yellowish-orange. * **Condition:** The prawns appear fresh and are in water, suggesting they are alive. Small air bubbles are visible on the surface of the water and adhering to the carapaces of some prawns. * **Water:** The bottom of the container is filled with a clear liquid, presumably water, which partially submerges the prawns. Light reflections are visible on the water's surface. * **Container:** The background is the interior of a dark, smooth-sided container, which provides a contrasting backdrop to the lighter-colored prawns. The container's surface is generally uniform in color, with some subtle variations due to water and lighting. * **Arrangement:** The prawns are loosely arranged and overlap each other, facing various directions without a specific pattern.