Ontogenetic development of
the digestive system in California halibut (Paralichthys californicus)
with notes on feeding practices
E. Gisbert, R.H. Piedrahita, D.E. Conklin-2004
Aquaculture, 232(1-4): 455-470
Abstract:
The development of the digestive tract and accessory
glands in California halibut (Paralichthys californicus) is described
from hatching to metamorphosis (42 days post-hatch, dph) at 18 °C.
Differentiation of the alimentary canal into the buccopharynx, esophagus,
pre- and postvalvular intestine, and rectum was complete by 3 dph (2.7±0.1
mm standard length, SL) coinciding with the time of first feeding. Zymogen
granules (pancreatic enzyme precursors) were detected in the exocrine
pancreas 1 day before the onset of exogenous feeding and their number
increased after first feeding, confirming the importance of pancreatic
secretions during the agastric period of larval development and their
genetically rather than dietarily induced secretion. The stomach was
morphologically differentiated at 27–30 dph (7.2–7.5 mm SL) coinciding
with the onset of eye migration. At this stage, gastric glands were abundant
in the fundic region and cardiac and pyloric regions were also clearly
distinguishable. Supranuclear bodies were observed in the postvalvular
intestine throughout the study period, although the number decreased as the
stomach differentiated and extracellular digestion took place. The reduction
of supranuclear bodies might be due to a change in the protein digestion
mechanism. Histological observations showed that Artemia-fed larvae
had almost intact nauplii in the postvalvular intestinal lumen and rectum,
suggesting a fast intestinal transit in California halibut larvae, and a
limited availability of nutrients from brine shrimp nauplii. Special
attention might be required in rearing tanks during the first week of
exogenous feeding, since the desquamation of the esophageal epithelium and
the absence of mucous secretion due to the lack of functional goblet cells
may promote bacterial infections under poor water quality conditions.