Teresa A. Noeske

Effects of Photoperiod and Feeding Schedule on Diel Variations of Locomotor Activity, Cortisol, and Thyroxine in Goldfish

Abstract Goldfish Carassius auratus held on a 14L:10D (14-hour-light:10-hour-dark) photoperiod and fed once daily at unscheduled times during light and darkness had a diurnal activity pattern beginning about light onset; this rhythm lasted at least 3 days when fish subsequently were held in constant light or constant darkness. When goldfish were fed once daily at scheduled times during a 12L:12D photoperiod (the schedule varying among treatments with respect to light and darkness), their activity was entrained by the feeding time, and the activity cycle persisted through 3–10 days of starvation. Serum-cortisol concentrations also were entrained by feeding regimen, peaking 0–6 (often 4) hours before feeding, and mean daily titers were unaffected by the time of day feeding occurred. Serum-thyroxine concentrations, in contrast, were entrained by photoperiod, though daily mean titers were affected by feeding time. Thus, feeding schedule, when it provides a consistent cue, overrides photoperiod to entrain cycl...

Circadian Feeding Time Affects Growth of Fish

Abstract Goldfish Carassius auratus were maintained on a 12L:12D (12-hour-light:12-hour-dark) photoperiod at 14 C and fed 1% of body weight once daily for 3 weeks. The fish had differences in growth depending on the feeding time relative to the light-dark cycle: Fish fed 18 hours after light onset (6 hours into darkness) grew more than others. Common carp Cyprinus carpio were maintained on a 16L:8D photoperiod at 15 C and fed 2% of body weight at one of six feeding times for 5 months. There were no consistent growth differences among treatments, nor any apparent debilitating effects of long-term enforced feeding times on common carp. The feeding time most conducive to body-weight gain appears to vary with the season and among cultured fish species. Timing the daily meal may be a valuable tool for aquaculture.

Timing of a single daily meal and diel variations of serum thyroxine, triiodothyronine and cortisol in goldfish carassius auratus

Two groups of goldfish were maintained on a 12L:12D photoperiod at 19°C and fed either at 0800 (light onset) or 1600 h daily. After 3 weeks, blood samples were taken at one of six times of day and the serum was analyzed for thyroxine, triiodothyronine, and cortisol by radioimmunoassay. Fish fed in the morning had significant diel variations in circulating titers of thyroxine and cortisol, those fed in the afternoon had significant variations of thyroxine and triiodothyronine. Meal feeding appeared to entrain, and phase shift, the cortisol rhythm but not the rhythms of thyroid hormones. These results are briefly discussed in light of the effects of timing the daily meal on weight gain in fish.

Effects of Thermocycles on Body Weight Gain and Gonadal Growth in the Goldfish, Carassius auratus

Abstract Goldfish subjected to increased temperatures at one of six different times of day had significant differences in weight gain and testicular growth depending on the time of treatment. Depending on the time of day the thermocycle was initiated, weight gain and testicular growth could be either stimulated, inhibited, or equal to that in fishes subjected to constant heat or constant cold. Heat applied during the last 4 h of darkness was particularly conducive to weight gain and testicular growth. The results of this study may have important implications for aquaculture.

Diel Variations in Sensitivity of Fishes to Potentially Lethal Stimuli

Abstract Fathead minnows (Pimephales promelas) and golden shiners (Notemigonus crysoleucas) exhibited differences in sensitivity to potentially lethal levels of chlorine, formalin, or heat, depending on the time of day of treatment.

The Influence of Ambient Temperature on the Daily Variation of Serum Cortisol in the Banded Killifish, Fundulus diaphanus

Abstract Separate groups of banded killifish, Fundulus diaphanus, were maintained on a LD 12:12 photoregime at either 5° or 20°C for a total duration of 16 days. Following this acclimation period, blood samples were taken by cardiac puncture at six different times of day and analyzed for serum cortisol by radioimmunoassay. Fish acclimated to 20°C had a unimodal daily pattern of serum cortisol with the peak concentration occurring during the four hour period before the onset of light. The daily pattern of cortisol of the fish acclimated to 5°C was bimodal with peak cortisol values measured at the onset and the offset of light. These thermally induced changes in cortisol hormone patterns may be related to other temperature dependent seasonal changes such as the annual cycle of reproductive development or changes in the time of daily locomotor activity.