Now showing items 1-4 of 4

    • Article

      Development of the digestive tract of milkfish, Chanos chanos (Forsskal): Histology and histochemistry 

      RP Ferraris, JD Tan & MC de la Cruz - Aquaculture, 1987 - Elsevier
      The digestive tract of the newly hatched milkfish larva is a simple undifferentiated tube. Three days after hatching, differentiation of the esophagus begins with development of mucous-secreting cells. At this time, the intestine can be distinguished from the anterior portion of the digestive tract by its tall columnar cells with centrally located nuclei and brush border with cytoplasmic projections. After 14 days, mucosal folds develop in the esophagus. In 21-day-old larvae, the stomach differentiates into the cardiac and pyloric regions while goblet cells start to develop in the intestine. In fish undergoing metamorphosis (≥ 42 days old), the mucosal cells of the cardiac stomach develop into two distinct cell types: the columnar cells which make up the folds nearest the lumen, and the cuboidal cells which constitute the gastric glands. The cardiac stomach is the only region in the digestive tract where mucus secretion is not acidic. From 3-day-old larvae up to the older stages, alkaline phosphatase is localized only at the brush border of the intestinal epithelial cells. Aminopeptidase is also found only in the brush border of enterocytes, but only in 21-day and older milkfish. Intestinal esterases are present not only in the brush border but are also diffusely distributed in the cytoplasm of enterocytes of 3-day or older fish. Esterase is also found in both the columnar and gland cells of the cardiac stomach, but only in postmetamorphic (60-day or older) fish. These morphological and histochemical changes of the gut seem to parallel dietary and habitat shifts throughout development, which encompasses life stages spent in pelagic, coastal or inland waters.
    • Article

      A histological study of the hypophysial-gonadal system during sexual maturation and spawning in the milkfish, Chanos chanos (Forskal) 

      JD Tan - Journal of Fish Biology, 1985 - Wiley-Blackwell
      The pituitary gland of the milkfish, Chanos chanos, was studied at different stages of sexual maturation and spawning. Consecutive median sagittal sections were treated with a range of stains to demonstrate the different cell types and regions. The milkfish pituitary consists of a neural component, the neurohypophysis, and an epithelial component, the adenohypophysis, which in turn consists of three regions: the rostral pars distalis (RPD), proximal pars distalis (PPD), and pars intermedia (PI). However, unlike most teleosts, the pituitary gland of the milkfish is encased in a bony chamber, has dorsal and ventral lobes and extends anteriorly from its point of origin at the base of the brain. PAS (+) basophils are found in all regions of the adenohypophysis, but mostly in the proximal pars distalis. These cells undergo hypertrophy and hyperplasia during sexual maturation, shrinkage and degranulation during spawning.
    • Article

      The in vitro effects of cyclic nucleotides, cyanoketone, and cycloheximide on the production of estradiol-17β by vitellogenic ovarian follicles of goldfish (Carassius auratus) 

      JD Tan, S Adachi & Y Nagahama - General and Comparative Endocrinology, 1986 - Academic Press
      The effects of human chorionic gonadotropin (HCG), forskolin, cyclic nucleotides, the phosphodiesterase inhibitors IBMX and theophylline, cyanoketone, and cycloheximide on the production of estradiol-17β by isolated ovarian follicles of vitellogenic goldfish (Carassius auratus) were examined using 18-hr incubations. HCG and all test agents which are known to increase intracellular concentrations of cAMP significantly stimulated the production of estradiol-17β. However, dibutyryl cGMP was unable to stimulate estradiol-17β production at any concentration used (1–10 mM). Cyanoketone at a concentration of 1 μg/ml completely blocked forskolin-induced estradiol-17β production. Even in the presence of cyanoketone, however, forskolin stimulated conversion of exogenous testosterone to estradiol-17β in a dose-dependent manner, suggesting the involvement of an adenylate-cyclase system in the induction of aromatase activation by vitellogenic follicles of goldfish. Cycloheximide also completely abolished HCG-induced estradiol-17β production when this inhibitor was added within the first 1 hr after the addition of HCG. These results provide evidence that the stimulation of estradiol-17β by goldfish vitellogenic follicles in response to HCG is dependent upon the synthesis of new protein.
    • Article

      Shift in steroidogenesis in the ovarian follicles of the goldfish (Carassius auratus) during gonadotropin-induced oocyte maturation 

      Y Nagahama, FW Goetz & JD Tan - Development, Growth and Differentiation, 1986 - Japanese Society of Developmental Biologists
      Both partially purified chum salmon gonadotropin and 17α-hydroxyprogesterone stimulated in vitro production of testosterone by postvitellogenic follicles of goldfish (Carassius auratus). Chum salmon gonadotropin further enhanced the conversion of exogenously supplied 17α-hydroxyprogesterone to 17α, 20β-dihydroxy-4-pregnen-3-one. The increased medium concentrations of 17α, 20β-dihydroxy-4-pregnen-3-one were associated with the induction of final oocyte maturation.

      The capacity of postvitellogenic follicles to produce steroids in response to exogenous 17α-hydroxyprogesterone was examined in females at various stages of final oocyte maturation following the administration of human chorionic gonadotropin in vivo combined with elevation of holding temperature. The maximum production of testosterone in response to 17α-hydroxyprogesterone was obtained in follicles from initial controls. In contrast, 17α 20β-diOHprog production was very low in initial controls and markedly increased during oocyte maturation (3–6 hr following injection), followed by a significant decrease in follicles collected at 15 hr. Estradiol-17β production by the follicles was very low at any stages of gonadotropin-induced oocyte maturation. These results suggest that gonadotropin-induced shift in the biosynthetic pathway in the follicle from the secretion of predominantly testosterone to 17α, 20β-dihydroxy-4-pregnen-3-one secretion is a prerequisite step for the induction of oocyte maturation in goldfish.