The giant freshwater prawn, Macrobrachium rosenbergii, is a large shrimp extensively used in aquaculture whose grooming behaviors were analyzed in this study. Macrobrachium rosenbergii exhibits three unique male morphotypes that differ in their behavior, morphology and physiology: small-clawed males (SM), orange-clawed males (OC) and blue-clawed males (BC). The largest and most dominant males, BC males, are predicted to have significantly different grooming behaviors compared to females and the other two male morphotypes. These BC males may be too large and bulky to efficiently groom and may dedicate more time to mating and agonistic interactions than grooming behaviors. Observations were conducted to look at the prevalence of grooming behaviors in the absence and presence of conspecifics and to determine if any differences in grooming behavior exist among the sexes and male morphotypes. Significant differences in the grooming behaviors of all individuals (females and male morphotypes) were found. BC males tended to have the highest grooming time budget (percent of time spent grooming) while SM males had a relatively low grooming time budget. The grooming behaviors of the male morphotypes differed, indicating while these males play distinct, separate roles in the social hierarchy, they also have different grooming priorities. The conditions in which Macrobrachium rosenbergii are cultured may result in increased body fouling, which may vary, depending on the grooming efficiencies and priorities of these male morphotypes. Overall, grooming behaviors were found to be a secondary behavior which only occurred when primary behaviors such as mating, feeding or fighting were not present.
Setae are vital in grooming activities and aiding in the removal of epibionts and sedimentary fouling from the body surfaces of decapod crustaceans. Thus, the setal structures and their arrangement on the grooming appendages and sensory structures of the commercially important shrimp, Macrobrachium rosenbergii, were examined using scanning electron microscopy. Macrobrachium rosenbergii is extensively grown in aquaculture and exhibits unique male morphological forms, termed morphotypes. The three male morphotypes are termed blue-clawed males, orange-clawed males, and small-clawed or undifferentiated males and all three differ in their dominance, behavior, body morphology, and reproductive success. Seven setal types, two of which have never been described in the literature, are identified on the grooming appendages (third maxillipeds, first, second, and fifth pereopods) and antennae: simple, serrate, serrulate, spiniform, pappose, crinoid, and spinulate. The latter two setae are newly identified. Certain setal types, such as serrate and serrulate setae were located and associated with specific grooming appendages such as the first pereopods. The types of setae on the grooming appendages varied among females and male morphotypes and the novel setal types (crinoid and spinulate) were found only on two of the male morphotypes. A literature review of terminology related to the structure of setae and setal types in decapod crustaceans is offered as the usage of various terms is ambiguous and conflicting in the literature. The intention of this review is to provide future authors with a comprehensive collection of terms and images that can be used to describe various aspects of setal morphology in decapods.
The giant freshwater prawn, Macrobrachium rosenbergii (De Man, 1879), lives in freshwater environments of the Indo-West Pacific region and is commonly farmed. Males transition into three male morphotypes that differ in behavior and morphology. Small-clawed males (SM) molt into orange-clawed males (OC) that molt into the harvested and largest blue-clawed males (BC). Grooming behaviors can remove fouling such as sediment particles, bacteria, and other organisms, all of which are commonly found in the natural environment as well as in aquaculture environments. Because individuals of this species groom their bodies frequently, especially the gills, the objective of the study was to observe gills of male morphotypes and females and evaluate their fouling levels and types using light microscopy, bacterial counts, and scanning electron microscopy. The male morphotypes and females are fouled differently, with grooming behaviors being effective in removing sedimentary and bacterial fouling from the gills. Although their relative efficiencies in removing fouling materials from the gills were not statistically significant, OC and BC exhibited contrasting gill fouling patterns with higher bacterial than sedimentary fouling in the former but the opposite in the latter. This difference may be attributed to differential levels of fouling related to variation in behavioral priorities, grooming behaviors, and morphology. Control of bacterial and sedimentary fouling in aquaculture could have large implications on the quality and survival of harvested individuals.
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