Pineal control of ultradian rhythms and short-term activity in a cyprinid fish, the lake chub, Couesius plumbeus

Diel activity patterns of lake chubs and other fishes in a temperate stream

Baited and unbaited minnow traps were set in Catamaran Brook and the Little Southwest Miramichi River, New Brunswick, and checked every 4 h to determine the diel activity pattern of four species of stream-dwelling fish (threespine stickleback (Gasterosteus aculeatus), juvenile white sucker (Catostomus commersoni), blacknose dace (Rhinichthys atratulus), and lake chub (Couesius plumbeus)). Secondary goals were to determine whether the presence of bait inside minnow traps affected the diel patterns of captures and to compare patterns of lake chub captures in minnow traps with movement through a nearby fish-counting fence. All fish except lake chubs were diurnal, although strict diurnality was less obvious when bait was present in the traps. Lake chubs, which are normally diurnal in the laboratory, were captured mostly near dawn or dusk in unbaited traps, throughout the day in baited traps, and mostly at night at the fish-counting fence. We infer that chubs are active mostly at dawn or dusk, except (i) when strong food cues are present, in which case their activity may extend into the day, and (ii) during the spawning migration, when they move mostly at night. Relative inactivity by chubs during the day may be caused by the presence of piscivorous birds such as kingfishers and common mergansers, whose hunting efficiency may be higher under brighter light.

Day-night rhythms of shoaling behavior in goldfish: opioid and pineal involvement

Intracerebroventricular (ICV) administration of the opioid peptide, beta-endorphin (5.0 pg/g) to goldfish, Carassius auratus, significantly increased the cohesiveness and duration of shoaling ('bout' length) in shoals of five fish, as well as decreasing the latency of shoal formation in response to an external disturbance, while a higher dose of beta-endorphin (15 pg/g) decreased shoaling. There were day-night rhythms in shoaling and in the extent of the facilitatory effects of beta-endorphin (5.0 pg/g) on shoaling behavior, the fish displaying significantly greater shoaling responses in the day than during the night. The facilitatory effects of the low dose of beta-endorphin were blocked by systemic administration of naloxone (1.0 mg/kg), while ICV administrations of naloxone (1.0 pg/g) decreased daytime shoaling behavior. Removal of the pineal gland disrupted the day-night rhythm of shoaling, reducing daytime levels of shoaling. In addition, pinealectomy reduced the stimulatory effects of beta-endorphin (5.0 pg/g) on shoaling, and attenuated the day-night rhythms in the effects on beta-endorphin on shoaling. These results suggest that both opioid systems and the pineal gland influence shoaling behavior and the expression of its day-night rhythm in goldfish.

The effects of constant light and constant darkness on daily changes in the morphology of the pineal organ in the goldfish, Carassius auratus

The fine structure of photoreceptor cells in the pineal organ of the goldfish was found to vary quantitatively over a 24-hour period. Stereological analysis revealed significant daily changes in the volume of the cell and inner segment, nuclear volume and nucleolar diameter, volume of endoplasmic reticulum and Golgi bodies, area of both rough and smooth endoplasmic reticulum, and number of vesicles associated with each Golgi body. Peak values of these variables occurred either during the dark phase or latter part of the light phase. These findings agree closely with those reported in higher vertebrates, and suggest that metabolic activities, and possible secretory functions, of the pineal organ of fishes are synchronized to the light:dark cycle. Daily changes in these variables generally persisted in fish exposed to constant darkness for seven days, with the peak in these rhythms coinciding closely with those observed in fish exposed to a light:dark cycle. In contrast, the rhythms in all variables were abolished in fish kept in continual light for seven days. Photoreceptor cells from fish exposed to continuous light had larger nucleoli and greater amounts of rough endoplasmic reticulum indicating a further effect of light on pineal metabolism in lower vertebrates.