The gastric sieve of penaeid shrimp species is a sub-micron nutrient filter

Abstract

Unlike vertebrates, the penaeid shrimp stomach is of ectodermic origin and is thus covered by a cuticle that is sloughed upon molting. It is composed of two chambers, here called the anterior and posterior stomach chambers, ASC and PSC respectively. The PSC contains a filtration structure variously called a pyloric filter, filter press, gastric filter or gastric sieve (GS) and the latter will be used here. The GS resembles an elongated, inverted-V, dome-like, chitinous structure with a midline ridge that is integral to the ventral base of the PSC. The dome surface is covered with a carpet-like layer of minute, comb-like setae bearing laterally-branching setulae. This carpet serves as a selective filter that excludes large partially-digested food particles but allows smaller particles and soluble materials to enter hepatopancreatic ducts that conduct them into the shrimp hepatopancreas (HP) where further digestion and absorption of nutrients takes place. Although the GS function is well known, its exclusion limit for particulate material has not been clearly defined. Using histological and ultra-structure analysis, we show that the GS sieve pore diameter is approximately 0.2-0.7 μm in size, indicating a size exclusion limit (SEL) of substantially less than 1 μm. Using fluorescent microbeads we show that particles of 1 μm diameter could not pass the GS but that those 0.1 μm diameter did pass through to accumulate in longitudinal grooves and move onto the HP where some were internalized by tubule epithelial cells. We found no significant differences in these sizes between the species Penaeus monodon and Penaeus vannamei or between juveniles and adults in P. vannamei. This information will be of value for design of particulate feed ingredients such as nutrients, therapeutic drugs and toxin-absorbing materials that may selectively target the stomach, intestine or HP of cultivated shrimp.