F.J. Sánchez-Vázquez

A blind circadian clock in cavefish reveals that opsins mediate peripheral clock photoreception

Evolution during millions of years in perpetual darkness leads to mutations in non-visual opsin genes (Melanopsin and TMT opsin) and an aberrant, blind circadian clock in cavefish.

Effect of three feeding strategies (automatic, ad libitum demand-feeding and time-restricted demand-feeding) on feeding rhythms and growth in European sea bass (Dicentrarchus labrax L.)

Abstract We studied the effect of automatic-feeding (A), ad libitum demand-feeding (D) and time-restricted demand-feeding (RD) on the feeding rhythm and growth performance of European sea bass maintained under natural summer conditions. RD and A had access to feed during three meals a day of 1 h duration each (08:00–09:00, 16:00–17:00 and 00:00–01:00). Feeding demands in D showed daily rhythms that varied according to both water temperature and photoperiod. When submitted to system RD, their feeding patterns were strongly associated with periods of feed availability. Feeding strategies affected both biomass increase and feed efficiency ratio, the worst results being obtained in A. On the other hand, the feeding system had no effect on body composition nor on weight homogeneity of the different groups. These results showed that sea bass can adapt to different feeding strategies, although for maximum benefit to be gained from the diet, these strategies should reflect the feeding rhythms of the fish.

Annual Rhythms of Demand-Feeding Activity in Sea Bass: Evidence of a Seasonal Phase Inversion of the Diel Feeding Pattern

Seasonal changes in the phasing of diel feeding rhythms were investigated in sea bass held under natural conditions. Demand-feeding behavior was continuously monitored over a complete annual cycle in 10 groups of 15 fish maintained in an outdoors laboratory subjected to natural fluctuations of photoperiod (from 9.5h to 15h) and water temperature (from 13.2 degrees C to 27.4 degrees C). A double seasonal phase inversion was detected in all groups: fish that were diurnal in summer and in autumn changed to nocturnal in winter and returned to being diurnal in spring. Diurnal sea bass displayed a positive and stable phase relationship between the peak of the feeding phase and the daily acrophase of water temperature (phi l = 0.72h +/- 0.33h) and between the peak of the feeding phase and sunset (phi s = 2.94h +/- 0.53h), but both phi l and phi s became negative when sea bass shifted to nocturnalism in winter. The percentage of diurnal feeding behavior peaked in June (94.1%) and dropped in February (29.1%), following a cyclic dynamic modulated by both monthly photoperiod and water temperature. These results contribute to better understanding of the dual phasing behavior of sea bass, which exhibits diurnal or nocturnal behavior according to the time of the year so that flexibility in phasing may be advantageous for the fish to cope with seasonal changes in their environment.

Light-dark and food restriction cycles in sea bass: Effect of conflicting zeitgebers on demand-feeding rhythms

Sea bass, a fish species characterized by its dualistic feeding pattern, was investigated to study the synchronizing effect of light and food on the demand-feeding rhythm. Nocturnal and diurnal sea bass, both in groups and individually, were exposed to restricted-feeding (RF) and light-dark (LD) cycles of different periods. The phase relationship between both zeitgebers was also studied. The results show that food-demand rhythms synchronize to periodic food availability under constant light conditions (DD) and that there is a partial coupling between food-entrained and light-entrained activity under conflicting zeitgebers (LD 13:13 h and RF 4:20 h), suggesting the existence of a feeding entrainable oscillator (FEO) in addition to the master light entrainable oscillator (LEO). In some cases, food availability restricted to the light or dark phase contrary to that of the previous feeding phase changed a diurnal feeding pattern into nocturnal and viceversa, suggesting that food can be one of the switching factors that decides whether the circadian system of sea bass is nocturnal or diurnal. However, the fact that the feeding pattern of some fish was unrelated with the phase in which food was available suggests that other internal and/or external factors could be involved in the temporal flexibility of sea bass.

Demand feeding and locomotor circadian rhythms in the goldfish, Carassius auratus: Dual and independent phasing

In contrast to the common diurnal and nocturnal ways of life, some fish species have been shown to have a dual phasing behaviour. Therefore, the daily pattern of behaviour is not always rigidly confined to the light or dark phase and a diurnal fish may become nocturnal and vice versa. In the present study, the locomotor and feeding activities of single goldfish were simultaneously investigated to examine the existence of such dual behaviour. Nineteen goldfish weighing 97.2 g on average were placed individually in 35-1 glass tanks equipped with an infrared sensor and a newly developed self-feeding device. Fish were exposed to a light:dark (LD) 12:12 h cycle, constant darkness (DD), and 45:45 min LD pulses to study endogenous rhythmicity. Under LD 12:12, the daily pattern of behaviour differed between individual fish; some goldfish were diurnal and others were nocturnal. Furthermore, some of them displayed an extraordinary flexibility in phasing because they were light active but dark feeding, and vice versa. Generally, goldfish tended to be day active, although their feeding habits appeared equally distributed between light and dark phases. Under DD, goldfish showed free-running rhythms that averaged 25.3 +/- 1.8 h and 24.4 +/- 1.7 h for locomotor activity and feeding, respectively, but that were slightly shorter under LD pulses. These results indicate that the type of phasing of locomotor activity did not necessarily decide the feeding phase; much of this is explained by the fact that goldfish were self-fed. Flexibility in phasing and a certain degree of independence between locomotor and feeding activities could be seen as an adaptative response of the highly adaptable circadian system of fish.

Feeding entrainment of locomotor activity rhythms, digestive enzymes and neuroendocrine factors in goldfish.

The existence of food anticipatory activity (FAA) in animals subjected to daily feeding schedules seems to be mediated by a feeding-entrainable oscillator (FEO). Such an FEO may help in anticipating meal time and so optimizing food acquisition and nutrient utilization. In this study we investigated the existence of FAA and whether digestive enzymes, plasma cortisol, hypothalamic NPY and gastrointestinal tract (GIT) and plasma melatonin were entrained by periodic feeding in goldfish. We observed that periodically fed goldfish showed FAA in locomotor activity as well as in amylase and NPY. Alkaline protease and GIT melatonin were higher after feeding, whereas plasma cortisol levels were reduced. Plasma melatonin remained unmodified before and after meal time. These results suggested that scheduled feeding entrained both behavioral and certain physiological patterns in goldfish, FAA being of adaptive value to anticipate a meal and prepare the digestive physiology of fish.

Feeding entrainment of locomotor activity rhythms in the goldfish is mediated by a feeding-entrainable circadian oscillator

Abstract Periodic food availability can act as a potent zeitgeber capable of synchronizing many biological rhythms in fishes, including locomotor activity rhythms. In the present paper we investigated entrainment of locomotor rhythms to scheduled feeding under different light and feeding regimes. In experiment 1, fish were exposed to a 12:12 h light/dark cycle and fed one single daily meal in the middle of the light phase. In experiment 2, we tested the effect of random versus scheduled feeding on the daily distribution of activity. During random feeding, meals were randomly scheduled with intervals ranging from 12 to 36 h, while scheduled feeding consisted of one single daily meal set in the middle of the light or dark phase. Finally, in experiment 3, we studied the synchronization of activity rhythms to feeding under constant darkness (DD) and after shifting the feeding cycle by either advancing or delaying the feeding cycle by 9 h. The results revealed that goldfish synchronized to feeding, overcame light entrainment and significantly changed their daily distribution of activity according to their feeding schedule. In addition, the daily activity pattern modulated by feeding differed between layers: a peak of activity being noticeable directly after feeding at the bottom, while an anticipatory behaviour was obvious at the surface of the tank. Under DD and no food, free-running rhythms averaging 25.5 ± 1.9 h (mean ± SD) were detected. In conclusion, some properties of feeding entrainment (e.g. anticipation of the feeding time, free-running rhythms following termination of periodic feeding, and the stability of ø after shifting the feeding cycle) suggested that goldfish have (a) separate but tightly coupled light- and food-entrainable oscillators, or (b) a single oscillator that is entrainable by both light and food (one synchronizer being eventually stronger than the other).

Daily locomotor activity and melatonin rhythms in Senegal sole (Solea senegalensis).

The daily locomotor and melatonin rhythms of the Senegal sole, a benthonic species of increasing interest in aquaculture, are still unknown, despite the fact that such knowledge is of prime importance for optimising its production. The aim of the present research was therefore to investigate the daily rhythms of locomotor activity and melatonin in the Senegal sole. For this purpose, the individual locomotor activity rhythms of fish were registered using a photocell. Plasma and ocular melatonin rhythms were studied in animals reared in circular tanks placed in earth under an LD 12:12 light regime and 16-18 degrees C temperature range (spring equinox). Blood and eye samples were taken every 3 h during a complete 24-h cycle. The impact of a light pulse in the middle of the dark period (MD) on plasma melatonin was also studied. Locomotor activity was mainly nocturnal, with 84.3% of the total activity occurring during darkness. The levels of plasma melatonin were higher at night (55 pg/ml) than during the day (2 pg/ml), while ocular melatonin levels appeared to be arrhythmic. Both weight and melatonin content were found to be significantly higher in the left eye in relation to the right eye. A light pulse in MD provoked a significant decrease in plasma melatonin levels. In summary, photoperiod is a key factor in synchronizing locomotor activity and melatonin rhythms in the Senegal sole, whose nocturnal habits should be taken into account for their rearing by aquaculture.

The influence of nocturnal vs. diurnal feeding under winter conditions on growth and feed conversion of European sea bass (Dicentrarchus labrax, L.).

Abstract European sea bass display predominantly nocturnal self-feeding patterns in winter and early spring, and this has been further examined by comparing the effect of night and day feeding on growth and feed conversion. To this end, three feeding regimes were compared: nocturnal automatic-feeding (NF), diurnal automatic-feeding (DF) and free access to self-feeders (SF). Under NF, feed was supplied in two meals differing in size (pre-dawn and post-dusk, 33.33: 66.67% of daily feed ration, respectively). In DF feed was supplied in three equally-sized meals (morning, afternoon and evening, 33.33: 33.33: 33.33% of daily feed ration). The experiment was carried out from January to April. Under SF, sea bass showed a phase inversion of daily feeding rhythms, which changed from an initial nocturnal to diurnal by the end of the experiment. Feeding strategies affected specific growth rate (SGR) and feed conversion ratio (FCR), the highest SGR and the lowest FCR being obtained with SF and NF treatments (SGR: 0.26±0.01 in NF vs. 0.19±0.01 in DF; FCR: 2.65±0.08 in NF vs. 3.73±0.17 in DF). The results demonstrate that feeding sea bass by night in winter, when they show nocturnal behaviour, may improve their growth and feed efficiency.

Effect of meal size modulation on growth performance and feeding rhythms in European sea bass (Dicentrarchus labrax, L.)

Abstract The combined effect of feeding time and meal size on the growth performance and feeding rhythms were studied in European sea bass maintained under natural summer–autumn conditions. Three feeding strategies were compared: a modulated automatic-feeding (MF), a fixed automatic-feeding (FF) and a free access to self-feeders (SF). Under MF, feed was supplied in meals of different size, three times a day (morning, afternoon and evening, 33.33:16.67:50% of daily feed ration, respectively) during the first (31 days) and second (35 days) period of the experiment, and twice a day (morning and evening, 33.33:66.67% of daily feed ration, respectively) during the third period (27 days). In FF feed was supplied in equally-sized meals, three times a day (morning, afternoon and evening, 33.33:33.33:33.33% of daily feed ration) in all three periods of the experiment. Under SF, fish showed a diurnal self-feeding pattern, with the greatest percentage of self-feeding activity concentrated in the evening. In MF and FF, although feed was delivered automatically, the trigger was left in the tank to register activations as an indicator of feeding activity. The trigger activation of both treatments MF and FF was associated with the time of feed delivery. Feeding strategies affected biomass increase, specific growth rate (SGR) and feed conversion ratio (FCR), the greatest biomass increase and highest SGR being obtained with MF and the poorest FCR with FF. The results demonstrate that automatic-feeding systems, in which the quantity of feed supplied is modulated in accordance with the natural feeding rhythms of sea bass, may improve growth and feed efficiency.