Effect of light intensity on the shoaling behaviour of the guppy (Poecilia reticulata)

It has been shown that the tendency of fish to shoal decreases as night falls. Much is known about shoaling in the daytime, however, little is known about the social behaviour of fish at night. Although the nocturnal disintegration of shoal structure is the conventional expectation for most diurnal marine fish, it has not yet been investigated for diurnal freshwater fish. This possibility has been investigated using guppies (Poecilia reticulata), collected from the wild, as an experimental model. Three preference tanks were used, one of which permitted only visual cues, another only olfactory cues and the other both visual and olfactory cues. Shoaling tendency was observed at four different light intensities (8 wt/m, 0·05 wt/m, 0·025 wt/m, 0·003 wt/m). These light intensities were chosen to mimic daylight, dawn/dusk, clear night and cloudy night conditions, respectively. Trials were carried out on randomly selected male guppies. Results indicated that with both modalities present fish significantly preferred the stimulus shoal at all light intensities. However with only one modality to indicate the presence of the shoal, fish showed no significant shoaling tendency at any of the diminished light intensities. A test of shoal cohesion at the four different light intensities was carried out on freely interacting fish. This test condition was chosen to mimic the situation of guppies in the wild. The results to date suggest that guppies continue to shoal during dusk (at low light intensities) but not during the night. These findings make an important contribution to our understanding of the social behaviour of fish at night and deserve further investigation.     

Shoaling behaviour in a surface-dwelling and a cave-dwelling population of a barb <Emphasis Type="Italic">Garra barreimiae</Emphasis> (Cyprinidae,Teleostei)

We studied shoaling behaviour in a species of fish (Garra barreimiae) from Oman. We compared two populations (a surface-dwelling and a cave-dwelling population) with different theoretical costs and benefits of shoaling. We measured the tendency to associate with a shoal of conspecifics. The stimulus shoal was confined to (1) clear Plexiglas cylinders in light, (2) wire-mesh cylinders in light, or (3) wire-mesh cylinders in darkness. The surface form exhibited a strong preference for the stimulus shoal during the experiments in light, but also in darkness, when only non-visual cues from the shoal could be perceived. The cave form did not show a preference when solely visual cues were available (Plexiglas cylinder). When non-visual cues from the shoal could be perceived (wire-mesh), the cave form did show a preference to associate with the shoal, but the shoaling tendency was considerably weaker than in the surface form. The shoaling tendency has probably been genetically reduced in the cave form.     

Shoaling in juvenile guppies: the effects of body size and shoal size

While factors affecting shoal mate choice have been examined extensively in adult guppies (Poecilia reticulata), few studies have focused on the shoaling behavior of juveniles. In this study, juvenile guppies were tested for their ability to shoal as well as their response to shoal mates of different body size and to shoals with different numbers of individuals. In dichotomous choice tests, 10-day-old guppies (mean body length=8.83 mm), 30-day-old guppies (13.17 mm) and 50-day-old guppies (18.6mm) were given the opportunity to swim near shoals of five fish or an empty chamber. In most cases, the juvenile fish demonstrated shoaling behavior, swimming near a group of fish rather than an empty chamber, regardless of the age of the stimulus shoal. When presented with two shoals, one of similar age and body size and one of dissimilar age and body size, only the 50-day-old guppies showed a significant preference for the age-matched shoal. Similarly, when choosing between a large shoal and a small shoal, only the 50-day-old guppies spent significantly more time near the larger shoal. Thus, while juveniles at each age shoaled, only 50-day-old fish demonstrated the shoal mate discrimination seen in adult fish.     

Size‐Assortative Shoaling in the Guppy (Poecilia reticulata): The Role of Active Choice

Many fish species exhibit size‐assortative shoaling, which is often thought to be driven by predation risk. Recent fieldwork has revealed that guppies (Poecilia reticulata) are more size assorted in high‐predation populations than in low‐predation ones. However, size assortment does nonetheless occur in some low‐predation populations, suggesting that predation is unlikely the sole driving force behind size‐assortment. Here, we investigated in the laboratory the potential role of active choice in size‐assortative shoaling in wild‐caught female guppies originating from two populations of the same river system in Trinidad. Small or large focal females from each population were offered a binary choice of shoaling with either four small female conspecifics or four large ones. Observed shoaling preferences depended on the body size of the focal fish, suggesting phenotype‐mediated conflict over group composition. Large focal fish preferred to shoal with the size‐matched stimulus shoal of large fish. In contrast, small focal fish did not shoal assortatively but also preferred to shoal with larger females. Our results suggest that size‐assortative shoaling in female guppies is likely to be due to factors other than active choice, such as habitat segregation and sexual harassment.     

Interpopulation Differences in Shoaling Behaviour in Guppies (Poecilia reticulata): Roles of Social Environment and Population Origin

In Trinidad, guppies (Poecilia reticulata) in high‐predation localities show more cohesive shoaling behaviour than those living with less dangerous predators in low‐predation sites. We evaluated the relative contributions of population origin (i.e. genetic and/or maternal effects) and social environment on the expression of shoaling by assessing the behaviour of juveniles reared in a range of social conditions. Focal individuals, offspring of guppies from populations from high‐ or low‐predation localities, were reared in a multifactorial experiment; we created four different social conditions by manipulating the source and demography of the conspecific residents with whom focal individuals interacted. We found that high‐predation fish displayed a stronger propensity to shoal than low‐predation ones. Our results also suggest a role for interactions between the source of the focal individuals, the demography of the group in which they were reared and the origin of the guppies with whom they were reared. Depending on their origin (high‐ vs. low‐ predation) and rearing density, our focal fish were more likely to shoal if they were reared with high‐predation residents. Learning from high‐predation residents, aggressive interactions with low‐predation residents and/or phenotype matching could have played a role in driving this effect of social environment. This effect of the phenotype of conspecifics on shoaling development would enhance heritable differences in shoaling propensity such that both could contribute to the well‐documented difference in shoaling behaviour of high‐ and low‐predation guppies in natural populations.     

The costs of becoming nocturnal: feeding efficiency in relation to light intensity in juvenile Atlantic Salmon

1. Most animals are active by day or by night, but not both; juvenile salmonids are unusual in that they switch from being predominantly diurnal for most of the year to being nocturnal in winter. They are visual foragers, and adaptations for high visual acuity at daytime light intensities are generally incompatible with sensitive night vision. Here we test whether juvenile Atlantic Salmon Salmo salar are able to maintain their efficiency of prey capture when switching between diurnal and nocturnal foraging.
2. By testing the ability of the fish to acquire drifting food items under a range of manipulated light intensities, we show that the foraging efficiency of juvenile salmon is high at light intensities down to those equivalent to dawn or dusk, but drops markedly at lower levels of illumination: even under the best night condition (full moon and clear sky), the feeding efficiency is only 35% of their diurnal efficiency, and fish will usually be feeding at less than 10% (whenever the moon is not full, skies are overcast or when in the shade of bankside trees). Fish were unable to feed on drifting prey when in complete darkness.
3. The ability of juvenile salmon to detect prey under different light intensities is similar to that of other planktivorous or drift-feeding species of fish; they thus appear to have no special adaptations for nocturnal foraging.
4. While winter drift abundance is slightly higher by night than by day, the difference is not enough to compensate for the loss in foraging efficiency. We suggest that juvenile salmon can nonetheless switch to nocturnal foraging in winter because their food requirements are low, many individuals adopting a strategy in which intake is suppressed to the minimum that ensures survival.     

UV matters in shoaling decisions

Shoaling behaviour in fish is influenced by numerous factors, such as familiarity, kinship, group size and shoal composition. Grouping decisions are based on both olfactory and visual cues. The visual system of many vertebrates is extended into the ultraviolet (UV) wave range as in three-spined sticklebacks (Gasterosteus aculeatus, L.). We investigated whether the presence or absence of UV wavelengths has an influence on shoaling behaviour in this species. Reproductively non-active three-spined sticklebacks were given the choice between two shoals, equal in numbers of individuals, which could be seen either through a UV-transmitting [UV(+)] or a UV-blocking [UV(-)] filter. Test fish preferred to join the shoal seen under UV(+) conditions. Due to differences in quantal flux between the UV(+) and UV(-) filters used, control experiments with neutral-density optical filters were performed in order to clarify the role of luminance. Here, test fish spent significantly more time near shoals that were seen in a darker environment, suggesting a potential trade-off between UV radiation and lower brightness during shoal choice.To our knowledge, these results demonstrate for the first time that shoaling decisions are influenced by UV wavelengths.     

Light intensity, prey detection and foraging mechanisms of age 0 year yellow perch

The ability of age‐0 year yellow perch Perca flavescans to detect prey using visual and mechano‐sensory input was examined during laboratory feeding trials at varying light intensities. Perch were highly effective predators and captured Daphnia pulicaria with 94% overall foraging success at light levels ranging from 0 to 3400 lx. Maximum average reaction distances (5·0 ± 0·8 cm, mean ±  s . e .) occurred in front of the fish at 3000 lx and significantly decreased as light intensities fell to <2 lx, with minimum reaction distances (2·8 ± 0·1 cm) observed in the dark. Following chemical ablation of the lateral line, yellow perch showed a significant reduction in reaction distance when compared to the untreated fish at 3000 lx, suggesting that the lateral line may augment visual prey detection at high light levels. A model was created to predict reaction distances for fish feeding with multiple sensory systems that can be applied to a variety of photic environments. This study provides a better understanding of the contribution of vision and the lateral line to prey detection, and relates the reaction distance of age‐0 year yellow perch to light intensities similar to those experienced in nature.     

The influence of light on the diel vertical migration of young-of-the-year burbot Lota lota in Lake Constance

The diel vertical distribution of young-of-the-year (YOY) burbot Lota lota in the pelagic zone of Lake Constance was compared to light intensity at the surface and to the light intensity at their mean depth. Lota lota larvae inhabited the pelagic zone of Lake Constance from the beginning of May until the end of August. From early June, after the stratification of the water column, fish performed diel vertical migrations (DVM) between the hypolimnion and epilimnion. The amplitude of DVM increased constantly during the summer and reached 70 m by the end of August. Lota lota started their ascent to the surface after sunset and descended into the hypolimnion after sunrise. As the YOY fish grew from May to August, they experienced decreasing diel maximum light intensities: in May and early June L. lota spent the day at light intensities >40 W m⁻², but they never experienced light intensities >0·1 W m⁻² after the end of June. From this time, L. lota experienced the brightest light intensities during dusk and dawn, suggesting feeding opportunities at crepuscular hours. The present study implies, that YOY L. lota in the pelagic zone of Lake Constance increased their DVM amplitude during the summer to counteract a perceived predation risk related to body size and pigmentation.     

Sex differences in dogfish behaviour: alternative activity patterns and habitat choice

Guppies are highly sexually dimorphic and females have been shown to mate preferentially with males with various visible traits. Guppies, however, have been shown to respond behaviourally to odour cues from conspecifics. Using a specially designed olfactory choice tank, we tested whether females (1) could detect other guppies on the basis of their olfactory cues alone, (2) preferred to associate with males or with females and (3) could distinguish between different males. Female guppies were found to associate preferentially with other guppies when given a choice between water containing cues from another fish and water containing no cues. When females were presented with olfactory cues from a male or a female, they preferred the female initially but most then reversed their decision and swam to the male. Females associated preferentially with certain males based upon olfactory cues alone. Males, however, preferred on the basis of olfactory cues were the least preferred for visual cues.     

Female preferences based on olfactory cues in the guppy (Poecilia reticulata)

Guppies are highly sexually dimorphic and females have been shown to mate preferentially with males with various visible traits. Guppies, however, have been shown to respond behaviourally to odour cues from conspecifics. Using a specially designed olfactory choice tank, we tested whether females (1) could detect other guppies on the basis of their olfactory cues alone, (2) preferred to associate with males or with females and (3) could distinguish between different males. Female guppies were found to associate preferentially with other guppies when given a choice between water containing cues from another fish and water containing no cues. When females were presented with olfactory cues from a male or a female, they preferred the female initially but most then reversed their decision and swam to the male. Females associated preferentially with certain males based upon olfactory cues alone. Males, however, preferred on the basis of olfactory cues were the least preferred for visual cues.     

Drift dispersal of mayfly nymphs in the presence of chemical and visual cues from diurnal drift- and nocturnal benthic-foraging fishes

1. The drift of Baetis thermicus nymphs in the presence of chemical, visual and hydrodynamic cues, considered individually and in combination, produced by different predatory fishes was examined experimentally in laboratory streams. Masu salmon ( Oncorhynchus masou ) and freshwater sculpin ( Cottus nozawae ) are typical drift- and benthic-foraging fishes, respectively.
2. Observations of fish swimming in the streams revealed differing diel periodicity between the species; sculpin were nocturnal foragers and salmon diurnal.
3. The drift rate of Baetis by night increased in the presence of chemical cues from sculpin, with other cues having no interactive effects. In contrast, the drift rate increased primarily in the presence of both chemical and, particularly, visual cues from salmon, although no additional effects were found for any non-visual cues. Visual cues could enable Baetis to assess precisely the predation risk from foraging salmon by day, whereas Baetis could not use visual cues to detect sculpin either at night, because of the low light intensity, or during the day, because of the low activity of sculpin at that time.
4. In natural streams, which are often inhabited by several predatory fish employing different modes of foraging, invertebrates may be able to precisely assess the risk and effectively to avoid predators by using cues unique to each.     

Does light intensity affect self‐feeding and food wastage in group‐held rainbow trout and white‐spotted charr?

The self‐feeding rhythms of rainbow trout Oncorhynchus mykiss and white‐spotted charr Salvelinus leucomaenis were studied when group‐held fishes ( n  = 10 per group) were fed using self‐feeders under two different light intensities (50 lx, 16 μW cm⁻² and 700 lx, 215 μW cm⁻²) during the light phase of the light‐dark cycle. Food wastage was also measured. At 50 lx, all groups of rainbow trout learned to operate the self‐feeder within 4 days, whereas it took up to 25 days for all groups at 700 lx. In contrast, all groups of white‐spotted charr learned self‐feeding within 17 days, irrespective of light intensity. These results, although non‐significant, suggest that lower light intensities can stimulate instrumental learning in rainbow trout, but not white‐spotted charr. In rainbow trout, the total number of trigger actuations for the entire experimental period was significantly higher at 50 rather than 700 lx, although this may have been related to delayed learning at 700 lx. There was no significant effect in white‐spotted charr. Growth rate (assessed using the thermal growth coefficient) was also higher in rainbow trout but not white‐spotted charr at 50 rather than 700 lx, although this difference was non‐significant. Light intensity had no significant effect on food wastage in either rainbow trout or white‐spotted charr, and it did not appear to affect the proportion of trigger actuations during the light phase. Clear diurnal feeding rhythms were observed in both species and these were classified into four categories: uniform, dawn, dusk and crepuscular. At 50 lx, fish from both species generally fed in temporally localized periods at either dawn and dusk, whilst feeding was predominantly uniform during the light phase at 700 lx.     

Ontogeny of numerical abilities in fish

Background

It has been hypothesised that human adults, infants, and non-human primates share two non-verbal systems for enumerating objects, one for representing precisely small quantities (up to 3–4 items) and one for representing approximately larger quantities. Recent studies exploiting fish''s spontaneous tendency to join the larger group showed that their ability in numerical discrimination closely resembles that of primates but little is known as to whether these capacities are innate or acquired.

Methodology/Principal Findings

We used the spontaneous tendency to join the larger shoal to study the limits of the quantity discrimination of newborn and juvenile guppies. One-day old fish chose the larger shoal when the choice was between numbers in the small quantity range, 2 vs. 3 fish, but not when they had to choose between large numbers, 4 vs. 8 or 4 vs. 12, although the numerical ratio was larger in the latter case. To investigate the relative role of maturation and experience in large number discrimination, fish were raised in pairs (with no numerical experience) or in large social groups and tested at three ages. Forty-day old guppies from both treatments were able to discriminate 4 vs. 8 fish while at 20 days this was only observed in fish grown in groups. Control experiments showed that these capacities were maintained after guppies were prevented from using non numerical perceptual variables that co-vary with numerosity.

Conclusions/Significance

Overall, our results suggest the ability of guppies to discriminate small numbers is innate and is displayed immediately at birth while discrimination of large numbers emerges later as a result of both maturation and social experience. This developmental dissociation suggests that fish like primates might have separate systems for small and large number representation.     

The effect of sex and shoal size on shoaling behaviour in Danio rerio

Male and female zebra fish Danio rerio were given choices of shoals that differed in sex and size. Male zebra fish preferred to associate with female shoals over male shoals, but had no preference when given a choice between a mixed‐sex shoal and either a male or female shoal. Female zebra fish showed no significant preference when given a choice between male and females shoals, nor between mixed‐sex shoals and either male or female shoals. When given choices between shoals of differing size, females preferred to associate with the larger shoal, whether or not they were composed of males or females. Males, however, had no preference for larger shoals over smaller shoals, whether or not they were composed of males or females. These results showed that male zebra fish were capable of distinguishing between males and females solely on the basis of visual cues. Furthermore, these results demonstrated a significant difference between the shoaling choices of male and female zebra fish, which may indicate a difference in the function of shoaling for the two sexes.     

Shoaling Decisions in Angelfish: The Roles of Social Status and Familiarity

Abstract Past research has shown that angelfish, Pterophyllum scalare , are capable of discriminating between shoals composed of familiar dominant and subordinate companions, whereas they show no preference for shoals of unfamiliar conspecifics. In this study, the relative importance of familiarity and social status (shoal factors) on the shoaling decision of juvenile angelfish, which also differed in social status (individual factor), was investigated as very little is known about such tradeoffs in fishes. Dominant and subordinate individuals were given the choice to shoal with a group of conspecifics composed of familiar dominants vs. unfamiliar dominants and composed of familiar subordinates vs. unfamiliar subordinates. The findings demonstrate that fish with different social status differed in their shoaling preference. Subordinate test fish showed a preferential association with familiar subordinates over unfamiliar subordinates, but preferred the unfamiliar shoal over the familiar one when both shoals were constituted by dominant individuals. The shoaling behaviour shown by dominant test fish, on the other hand, indicated no significant preference for any of the shoals regardless of their composition. A replicate preference test carried out 2 h 30 min after the first one indicated that the association pattern was relatively consistent. Results suggest that angelfish are able to differentiate between the stimulus shoals and demonstrate that the pervasive influence of familiarity on the shoaling decision may be restrained or overridden by the composition of the familiar shoals and the social status of the test fish.     

Diel distribution patterns of fishes in a temperate large lowland river

During the day, juveniles and typical inshore species in the lower Oder River, Germany, inhabited the littoral (0·05–1·50 m deep) while potamal species inhabited the mid‐channel (40–100 m from the banks). During the night, two behavioural groups were distinguished: 1) potamal species and large individuals of other species, moved from offshore to the littoral, and 2) nocturnal foraging species, became active and increased in inshore and offshore habitats. Inshore, the most significant differences at night was the increasing density of silver bream Blicca bjoerkna increasing both total biomass and total length of fishes caught. Offshore, the increasing density of whitefin gudgeon Gobio albipinnatus at night was most significant. Additional night electrofishing improved the assessment of the abundance, age and size structure of typical potamal fish species. It should be incorporated in large river fish monitoring programmes.     

Shoaling behaviour of sticklebacks infected with the microsporidian parasite, <Emphasis Type="Italic">Glugea anomala</Emphasis>

We compared the shoaling behaviour of three-spined sticklebacks, Gasterosteus aculeatus, infected with the microsporidian, Glugea anomala, to that of non-infected conspecifics. Infected fish lost significantly more weight than non-infected fish during a period of food deprivation, suggesting a metabolic cost to parasitism. In binary shoal choice tests, non-infected test fish showed an association preference for a shoal of non-infected over a shoal of infected conspecifics; infected test fish displayed no preference. Infected fish, however, showed a higher overall tendency to shoal than non-parasitised fish. Furthermore, infected fish occupied front positions within a mixed school. We consider the behavioural differences between infected and uninfected fish in the context of their potential benefits to the fish hosts and the parasites.     

Isolation and the development of shoaling in two populations of the guppy

Socially reared guppies Poecilia reticulata derived from two wild populations (Upper and Lower Aripo River, Trinidad) showed a significant relationship between body size and shoaling tendency, measured as the proportion of time spent in proximity to a bottle containing conspecifics. Larger females shoaled significantly more than smaller females. Fish from the high-shoaling population (Lower Aripo) showed significantly less shoaling behaviour when reared in isolation. In contrast, low-shoaling fish (Upper Aripo) demonstrated no significant change in their shoaling behaviour in response to social isolation.     

Juvenile convict cichlids shoaling decisions in relation to shoal size and age

Many animals form groups and socialize in response to evolutionary pressures such as predation, food availability, and mate acquisition. Evidence of social choice based on various phenotypic characters (Group Phenotypic Composition [GPC]) has been observed in several animal species. In addition to the physical characteristics of the social group, it is also interesting to consider how decisions of who to socialize with might be expected to change for an individual over time. Younger individuals with limited life experience may discriminate differently between social groups than older conspecifics who have had the opportunity to learn and who may be faced with different ecological or environmental pressures. Here, we used a traditional two‐choice design to explore the shoaling behavior of juvenile convict cichlids and determine whether the number of fish and/or the size/life stage of the individuals within a shoal influenced social choices. We found that juvenile convict cichlids spent more time shoaling with similarly sized juvenile individuals and also preferred to shoal with larger shoals, but not when shoals were comprised of adult fish. The size of the individuals in a shoal was a more influential factor than the size of the shoal itself. Size of individual juveniles was correlated with tendency to visit shoals, but was not correlated with overall time spent shoaling, regardless of shoal composition. As juveniles, convict cichlids can make discriminatory choices that are influenced by specific aspects of shoal composition.