George Delahunty

Diurnal variations in the physiology of the goldfish, Carassius auratus

Abstract Liver glycogen, liver lipid, liver triglycerides, plasma glucose, plasma total lipid, plasma cholesterol, plasma corticoids, hypothalamic serotonin and pituitary pro‐lactin levels were assayed at five times over a 24‐h period in Carassius auratus maintained under a specific photoperiod regime at various times throughout the year. Diurnal variations were observed in all parameters monitored. Daily variations of liver glycogen, plasma glucose, plasma lipid, plasma corticoids and hypothalamic serotonin were affected by time of feeding. Liver glycogen, plasma lipid and plasma corticoid levels were also affected by time of feeding. Diurnal variations of liver glycogen, plasma glucose and plasma lipid were influenced by light‐dark cycles. These data illustrate that feeding time, photoperiod and time of sacrifice are important considerations in the study of metabolic and hormonal parameters in fishes.

Effects of pinealectomy and melatonin treatment on liver and plasma metabolites in the goldfish, Carassius auratus

Abstract The effects of pineal removal on daily variations and levels of some liver and plasma metabolites were examined in the goldfish, Carassius auratus . Pinealectomy abolishes the liver glycogen daily variation and decreases hepatic glycogen levels in goldfish maintained on specific photoperiod regimes during spring and summer. Neither the daily variation nor the levels of hepatic glycogen are affected by pinealectomy during the fall. Pinealectomy alters the plasma glucose daily variation and increases the levels of this metabolite in fishes maintained on long photoperiods during the summer. During the fall the daily variation of plasma glucose is abolished by pinealectomy and blood sugar levels are decreased. The diurnal fluctuation of plasma lipid is altered by pinealectomy during the summer. Plasma lipid levels are elevated in pinealectomized fishes during winter, spring, and summer. The daily variation of liver lipid levels is altered by pinealectomy during the autumn. Melatonin treatment increases liver glycogen reserves in goldfish maintained on a long, but not a short, photoperiod during the spring. Plasma glucose levels are also elevated by melatonin treatment. Therefore, the pineal organ participates in regulating levels and daily variations of some metabolites. The influence of the pineal on metabolites varies with season and day length.

The effects of light reception on circulating estrogen levels in female goldfish, Carassius auratus: Importance of retinal pathways versus the pineal ☆

Abstract The effects of pinealectomy, optic tract section, or exposure to continuous darkness on serum estradiol-17β levels in the goldfish were examined during the spring and fall. Pineal removal had no effect on serum estrogen levels or GSI in either fall or spring. Optic tract section decreased serum estrogen levels in both spring and fall experiments. Ovarian regression was initiated in fish exposed to continuous darkness and optic tract-sectioned fish during the spring, but fish maintained in darkness exhibited no change in serum estrogen levels. Our data imply that it is primarily retinal pathways which mediate the effects of increasing daylength on goldfish ovarian development during the spring.

The effects of blinding, pinealectomy and exposure to constant dark conditions on gonadal activity in the female goldfish, Carassius auratus

SynopsisThe effects of pinealectomy, blinding, and exposure to constant darkness were examined in female goldfish during different seasons. Neither blinding nor pinealectomy under short or decreasing photoperiod conditions, nor exposure to constant darkness had an effect on ovarian activity in goldfish during fall and winter. In spring, constant darkness has an inhibitory effect on ovarian activity. Pinealectomy under increasing photoperiod conditions partially inhibits reproductive activity, but not to the extent of constant darkness. Blinding, under the same regime also inhibited to some extent the ovarian response to increasing photoperiod. Our data suggest that retinal pathways and the pineal organ are involved in the photosexual response to increasing day lengths.

Photoperiod-temperature interactions on liver and plasma metabolites in the goldfish, Carassius auratus

Abstract 1. 1. Plasma and liver metabolites were measured in goldfish after 3 weeks acclimation to one of four different photoperiod-temperature regimes (16L/8D-22°C; 16L/8D-13°C; 8L/16D-22°C; 8L/16D-13°C) during September and April. Samples were taken at the mid-light and mid-dark point of each photoregime. 2. 2. Photoperiod altered levels of plasma protein and plasma cholesterol. 3. 3. Temperature affected the levels of liver glycogen, plasma glucose, organic bound phosphorus and protein. 4. 4. Time of sampling was important in assessing both photoperiod and temperature effects on metabolites. 5. 5. Interaction between photoperiod and temperature was observed in the levels of liver glycogen and plasma glucose. The interaction was dependent on sampling time. 6. 6. Seasonal differences were noted in the day-night variation of specific metabolites and of the photoperiod effects on plasma cholesterol levels.

Effects of photoperiod on plasma corticoid levels in the goldfish, Carassius auratus—role of the pineal

Abstract 1. 1. The effects of photoperiod and pinealectomy on plasma corticoid levels in the goldfish (Carassius auratus) were examined. 2. 2. Plasma corticoid levels differed in goldfish maintained under different photoperiod regimes, but this response varied seasonally. 3. 3. Pinealectomy altered the effects of photoperiod on plasma corticoid levels but this effect varied with season. 4. 4. Plasma corticoid levels were correlated with ovarian activity. The effects of photoperiod on plasma corticoid levels appear to be related to the influence of light on reproduction. 5. 5. The alteration of plasma corticoid levels in pinealectomized fish may be due to the role this organ plays in mediating photoperiod effects on gonadal activity.

Does pinealectomy, anopsia or exposure to constant darkness affect pituitary prolactin levels in the goldfish,Carassius auratus L.?

SynopsisThe ef fects of exposure to constant darkness, anopsia and pinealectomy on pituitary prolactin levels in the goldfish were examined. Determination of prolactin was made in a polyacrylamide microelectrophoretic system coupled with densitometry. Neither pinealectomy nor anopsia had an effect on pituitary prolactin content in the fall. Exposure to constant darkness in the fall was without obvious effect, whereas such treatment in the spring resulted in significantly elevated pituitary prolactin content. Pinealectomy in the spring did not alter pituitary content, suggesting that the response to constant darkness is independent of the pineal organ, perhaps involving retinal or extra-retinal photoreception.