Ontogeny of digestive and immune system organs of larval and juvenile kelp grouper Epinephelus bruneus reared in the laboratory

ABSTRACT:   A histological examination was made of the ontogenetic development of the digestive and immune systems of the larval and juvenile kelp grouper Epinephelus bruneus reared in the laboratory. The liver, gall bladder, pancreas and the demarcating region between the intestines and rectum were formed within 3 days post-hatch (dph). During the preflexion phase (within 16 dph), revolution of the intestine concluded, and pharyngeal teeth and the mucous cells of the esophagus were differentiated. In the transitional period to the juvenile stage (25 dph), the blind sac of the stomach, gastric glands and pyloric caeca began to form. From the viewpoint of the differentiation phase of the adult-type digestive system, the kelp grouper is similar to Heterosomata, hitherto reported. The primordial thymus, kidney and spleen were present at 12, 1 and 6 dph, and the small lymphocytes in these lymphoid organs appeared at 21, 30 and 33 dph, respectively. The developmental sequence of the lymphoid organs and the appearance ages of the lymphoid organs and small lymphocytes in the lymphoid organs in the kelp grouper are similar to those of other marine fish previously reported, except for the Pacific bluefin tuna Thunnus orientalis .     

Gustatory receptor responses in marbled rockfish Sebastiscus marmoratus

Gustatory response of marbled rockfish Sebastiscus marmoratus was recorded from the facial nerve supplying the anterior palate. In amino acids, the lowest threshold was for L -proline at 10⁻⁶–10⁻⁵ M; in ATP-related substances, the value for inosine was approximately 10⁻⁵ M and in organic acids, the value for L -lactic acid was approximately 10⁻⁶ M. An almost complete self-adaptation was observed for stimulants after 5 s application. While a weak solution of L -lactic acid as adapting stimulus depressed the response to it completely, it did not appreciably affect the response to 10-times or more concentrated L -lactic acid solution. In contrast to a weak solution, a moderate solution caused a severe depression of the response to stronger solutions, resulting in a shift of the dose–response curve towards a high concentration range. Time for recovery from adaptation differed depending on chemicals and stimulus duration: for 10⁻⁴ M L -lactic acid, it took about 2.3 and 4.5 s for 1/2 recovery of response magnitude under unadapted condition from the adaptation after 1 s- and 5 s-stimulation, respectively. L -Lactic acid and L -alanine strongly depressed the response to each other, yielding a rightward shift of the dose–response curve. A similar profound cross-adaptation was also observed between inosine and 5'-inosinic acid. The possible role of gustation is discussed.