Abstract
Our investigation is focused on ontogenesis of the digestive system in Litopenaeus vannamei. The results reveal that in non-feeding stages the yolk mass is the indigenous source of food and until the fifth nauplius (N5) stage retained in foregut cavity, absorption is gradual in nauplius (N) stages while disappearance occurs at N6 stage. The anterior midgut caecum is discrete at N3 and it reaches maximum size in Z3; thereafter in successive stages it reduces in size and becomes a single structure in post-larval stage (P3–P4), named the anterior diverticulum. The lateral midgut caecum first appears at N6 stage and lengthens along both sides of the midgut and then ramifies to form lobes as larval development. Finally, these lobes become a compact structure, the hepatopancreas. The midgut lumen is quite apparent in N stages and only becomes wider in successive stages; it is without a cuticle lining and there is no difference among all investigated stages. The foregut in N stages is a simple tube and pyloric and cardiac chamber occurs in the third mysis (M3) stage. In the cardiac chamber of post-larval stages, folds were noted to increase gradually. The gastric mill is absent in all investigated larval stages (P1–P10). The pyloric chamber is smaller than the cardiac chamber and possesses a gland filter, which first appears in M3 stage and forms a more complete shape in forthcoming stages. The hindgut gland first appears in P2 and in successive stages it shows more protuberance and complexity. The hindgut or rectum is a simple tube. Cells of the digestive system in all feeding stages show the presence of acid mucins and general protein, while the inner margins of the foregut and connective tissues of the gland filter are positive for collagen.
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