Loss of shoaling preference for familiar individuals in captive-reared crimson spotted rainbowfish Melanotaenia duboulayi

Captive-reared rainbowfish Melanotonia duboulayi showed no preference for familiar individuals in an experiment examining shoaling preferences. Fortnightly re-examination of the shoaling preferences of the captive-reared population showed that the lack of preference for familiar individuals did not alter over an 8 week period. The same experiment performed on laboratory-reared offspring raised in isolated groups for 8 months since hatching also showed no preference for shoals consisting of familiar individuals. In contrast, trials performed on a wild population of M. duboulayi found a strong preference for familiar shoalmates, a result that is consistent with previous studies. The lack of shoaling preferences in captive-reared populations is probably the result of relaxed selection and inbreeding in the captive environment. The consequences of captive breeding for fish social behaviour are discussed with particular reference to hatchery production.     

A re-evaluation of the effect of shoalmate familiarity on the proliferation of alarm substance cells in ostariophysan fishes

A re-examination of data from Wisenden & Smith Journal of Fish Biology 50 , 799–808) suggests that fathead minnows Pimephales promelas adjust investment into epidermal alarm substance cells (ASC) facultatively based upon the level of perceived risk. When placed into a container with non-familiar shoalmates (relatively high risk) ASC production increased. This allows these individuals to attract a secondary predator better. When placed into a container with familiar shoalmates (relatively low risk) ASC production decreased. This may reflect increased effectiveness of a group antipredator response by familiar individuals, and/or the cost to inclusive fitness of attracting additional predators to the vicinity of their kin.     

Social familiarity and shoal formation in juvenile fishes

The potential influence of social familiarity in shoal‐choice decisions was investigated in two sympatric species of north temperate fishes, juvenile banded killifish Fundulus diaphanus and juvenile bluegill sunfish Lepomis macrochirus. Groups of socially familiar and unfamiliar conspecifics were formed in the laboratory using wild‐caught fishes. Juvenile F. diaphanus demonstrated a strong preference for familiar conspecific shoalmates, whereas juvenile L. macrochirus exhibited no preference for either unfamiliar or familiar conspecific shoalmates. The differential influence of familiarity on shoalmate choice in juveniles of these two species could be due to their different ecologies, local population densities and life histories.     

Preferences for familiar fish do not vary with predation risk in the European minnow

In the near-natural conditions of a fluvarium in the River Frome, U.K., European minnows Phoxinus phoxinus displayed schooling preferences for familiar conspecifics. Schools were composed of 75% familiar fish. The minnows in this river co-occur with many piscivores, the most notable being the pike Esox Iucius . The preference for familiar shoalmates was not increased by the threat of predatory attack from a model pike, despite the antipredator benefits afforded to individual members of schools of familiar fish.     

Can a minority of informed leaders determine the foraging movements of a fish shoal?

There is no information on whether the daily foraging movements of fish shoals are the result of chance, the collective will of all shoalmates, or the leadership of a few individuals. This study tested the latter possibility. Shoals of 12 golden shiners, Notemigonus crysoleucas, were trained to expect food around midday in one of the brightly lit corners of their tank. They displayed daily food-anticipatory activity by leaving the shady area of their tank and spending more and more time in the food corner up to the normal time of feeding. Past this normal time they remained in the shade, even on test days when no food was delivered. Most of these experienced individuals were then replaced by na?ve ones. The resulting ratio of experienced:na?ve fish could be 5:7, 3:9 or 1:11. On their own, na?ve individuals would normally spend the whole day in the shade, but in all tests the experienced individual(s) were able to entrain these more numerous na?ve fish out of the shade and into the brightly lit food corner at the right time of day. Entrainment was stronger in the 5:7 than in the 1:11 experiment. The test shoals never split up and were always led by the same fish, presumably the experienced individuals. These results indicate that in a strongly gregarious species, such as the golden shiner, a minority of informed individuals can lead a shoal to food, either through social facilitation of foraging movements or by eliciting following behaviour. Copyright 2000 The Association for the Study of Animal Behaviour.     

The Effect of Hunger on Shoal Choice in Golden Shiners (Pisces: Cyprinidae,Notemigonus crysoleucas)

When an animal has a choice of joining one group over another, its decision may depend on its relative vulnerabilities to predation and starvation. For example, a well-fed animal may choose a large group of individuals with body size matching its own because this gives good protection against predators, but a hungry animal may prefer smaller groups made up of smaller individuals because this decreases food competition. To test this idea, a choice between various shoals was given to golden shiners, Notemigonus crysoleucas, that were either well fed or deprived of food for 48 h. In a choice of 10 vs. 3 shoalmates, both well-fed and hungry shiners spent more time near the shoal of 10. In a choice of 20 vs. 3 shoalmates, both well-fed and hungry shiners again preferred the larger shoal, but in one replicate this preference was significantly weaker in the hungry fish. This reduced preference did not appear to be an artefact of increased mobility by hungry fish searching for food. In a choice between shoals of small vs. large conspecifics, small well-fed shiners, small hungry shiners, and large well-fed shiners preferred shoalmates with body size matching their own, but large hungry shiners preferred smaller individuals. These results are consistent with the hypothesis that hungry fish sacrifice safety from predation in their shoaling behaviour (by avoiding larger groups to a certain extent and by risking the oddity effect) so as to decrease food competition.     

The effect of physical condition and shoalmate familiarity on proliferation of alarm substance cells in the epidermis of fathead minnows

Ostariophysan fishes have specialized epidermal alarm substance cells (ASCs). In this study, metabolic cost to the production and maintenance of these cells was demonstrated. Fathead minnows Pimephales promelas were maintained on high or low food rations and, to test for the effect of social context on the number of ASCs, they were held with either zero or two shoalmates. Shoalmates were familiar (from the focal fish's shoal), or unfamiliar (from a shoal separated by 1 km from the focal fish's shoal). After 16 days, epidermal thickness, number of mucus cells and number of ASCs were all significantly greater for minnows on the high ration than for those on the low ration. Within the high ration group, physical condition was positively correlated with epidermal thickness and ASC number. The shoalmate treatment had no measurable effect on the epidermis. It was concluded that food availability determines investment into ASCs, inferring a trade-off between the cost of ASCs and the fitness benefits they accrue.     

Social Context Influences the Antipredator Behaviour of Fathead Minnows to Chemical Alarm Cues

Prey fishes, like many organisms under fluctuating predation threat, rely on multiple sources of information to accurately gauge current risk. This includes the use of chemical cues such as alarm cues from damaged conspecifics or familiar heterospecifics, as well as the odour of known predators. While each fish is well equipped with its own array of sensory abilities, they should also be alert to the behaviours of nearby neighbours who may have information they lack. In the present study, we tested the ability of fathead minnows to use social cues in combination with the odour of damaged conspecifics and heterospecifics to mediate the assessment of predation risk. Specifically, we tested whether the presence of a shoal of conspecifics or familiar heterospecifics would significantly change a minnow's antipredator behaviour when exposed to the odour of a damage‐release cue from a conspecific or ecologically similar heterospecific. The results of our study showed a significant interaction between the damage‐release cues to which the minnows were exposed and the presence/absence of shoalmates. These findings have important implications for the design of future investigations of antipredator responses because most studies of group‐living prey have been conducted on solitary subjects.     

Evolution of acoustic signals in Cyprinella: degree of similarity in sister species

Signal structure and behavioural context were examined in two sister species, the Tallapoosa shiner Cyprinella gibbsi and the tricolor shiner Cyprinella trichroistia , with two more distantly related species, the Ocmulgee shiner Cyprinella callisema and the whitetail shiner Cyprinella galactura , in order to test the hypothesis that more closely related species would share components of signals not shared with more distant relatives, and to look at the degree of divergence. The species examined differed in number and type of signal components, contexts and frequency under which calls were produced. While all species produced pulses arranged into pulse bursts, C. gibbsi and C. trichroistia shared unique call types, chirps and rattles, and C. galactura and C. callisema both produced the knock call type. The sister species shared more components of their call repertoire with each other than with the more distantly related C. galactura and C. callisema and clustered together based on courtship call similarity.     

Innate and Learned Shoaling Preferences Based on Body Coloration in Juvenile Mollies,Poecilia latipinna

Shoaling offers fish enhanced protection from predators through a phenomenon known as the confusion effect. This phenomenon depends on a high degree of phenotypic homogeneity within a shoal, which may confuse predators that have difficulty in targeting a single individual as prey. Accordingly, fish typically choose shoalmates with similar phenotypic characteristics to themselves. In the molly (Poecilia latipinna), dramatic differences in body coloration have been shown to affect shoalmate choice in adults. Here, we show that juvenile mollies (50 d old) were capable of shoaling and that early experience impacted shoalmate choice. When raised in isolation, mollies chose shoalmates with similar body coloration to their own. When raised with other juvenile mollies, test fish chose to associate with individuals of the same coloration as the fish with whom they had been reared. These results show that P. latipinna are capable of the behavioral plasticity that has been demonstrated in other fish species, and that early experience affects the impact of body coloration on shoaling decisions in this species.     

Red shiner invasion and hybridization with blacktail shiner in the upper Coosa River,USA

Human disturbance increases the invasibility of lotic ecosystems and the likelihood of hybridization between invasive and native species. We investigated whether disturbance contributed to the invasion of red shiner (Cyprinella lutrensis) and their hybridization with native blacktail shiner (C. venusta stigmatura) in the Upper Coosa River System (UCRS). Historical records indicated that red shiners and hybrids rapidly dispersed in the UCRS via large, mainstem rivers since the mid to late 1990s. We measured the occurrence and abundance of parental species and hybrids near tributary-mainstem confluences and characterized populations at these incipient contact zones by examining variation across morphological traits and molecular markers. Red shiners represented only 1.2% of total catch in tributaries yet introgression was widespread with hybrids accounting for 34% of total catch. Occurrence of red shiners and hybrids was highly correlated with occurrence of blacktail shiners, indicating that streams with native populations are preferentially colonized early in the invasion and that hybridization is a key process in the establishment of red shiners and their genome in new habitats. Tributary invasion was driven by post-F1 hybrids with proportionately greater genomic contributions from blacktail shiner. Occurrence of red shiners and hybrids and the relative abundance of hybrids significantly increased with measures of human disturbance including turbidity, catchment agricultural land use, and low dissolved oxygen concentration. Red shiners are a significant threat to Southeast Cyprinella diversity, given that 41% of these species hybridize with red shiner, that five southeastern drainages are invaded, and that these drainages are increasingly disturbed by urbanization.     

Familiarity-biased patterns of association shift with time among European minnows

Replicated, naturalistic mesocosms were used to investigate whether pre-existing preferences for familiar individuals decay when opportunities to form new alliances arise. In each trial, two groups of wild European minnows Phoxinus phoxinus were introduced to a common environment, and their association patterns monitored continuously over a 3 week period using passive integrated transponder (PIT) tags. Individuals within a group were familiar, but had no previous experience of the other group. European minnows associated initially with previously familiar individuals more frequently than expected by chance. This preference then diminished over a period of 2 weeks following their encounter with the unfamiliar group of fish and was not detectable by the third week. Instead, new association patterns resulting from non-random re-assortment of individuals over time were evident. The results show that new alliances between individuals form when wild shoals coalesce.     

Geographic independence and phylogenetic diversity of red shiner introductions

Identifying areas at risk of invasion can be difficult when the distribution of a non-native species encompasses geographically disjunct regions. Understanding genealogical relationships among native and non-native populations can clarify the origins of fragmented distributions, which in turn can clarify how fast and far a non-native species may spread. We evaluated genetic variation across the native and invasive ranges of red shiner (Cyprinella lutrensis), a minnow known to displace and hybridize with native species, to reconstruct invasion pathways across the United States (USA). Examination of mitochondrial cytochrome-b variation found that native range populations of red shiner fall into four highly divergent lineages that likely warrant species recognition. Introduced red shiner populations in the eastern and western USA are derived from only two of these lineages. Western USA populations originate from the mid-western and western genetic lineages, whereas eastern introductions derive only from the mid-western lineage. Western USA invasive populations exhibit fewer, but more diverse haplotypes compared to eastern USA invasive populations. We also recovered an undescribed, divergent lineage of Cyprinella that has been cryptically introduced into the western USA, which raises the possibility that hybridization has proceeded following secondary contact between previously allopatric lineages. Approximate Bayesian Computation modeling suggests that the disjunct distribution of red shiner across North America is an agglomeration of independent regional invasions with distinct origins, rather than stepwise advance of an invasion front or secondary introductions across regions. Thus localized control may be effective in managing non-native red shiner, including further spread to areas of conservation concern.     

Tendency to inspect predators predicts mortality risk in the guppy (Poecilia reticulata)

Although predator inspection behavior in fishes has become amodel system for examining game theoretical strategies suchas Tit for Tat, the direct costs of inspection behavior havenot been quantified. To begin quantifying such costs, I conductedan experiment that examined mortality due to predation as afunction of predator inspection in the guppy (Poecilia reticulata).Before being subjected to a "survivorship" experiment, guppieswere assayed for their tendency to inspect a predator. Groupswere then composed of six guppies that differed in their tendencyto inspect. These groups were placed into a pool containinga predator, and survivorship of guppies with different inspectiontendencies was noted 36 and 60 h later. Results indicate thatindividuals that display high degrees of inspection behaviorsuffer greater mortality than their noninspecting shoalmates.     

Cross-modal individual recognition in domestic horses (Equus caballus) extends to familiar humans

It has recently been shown that some non-human animals can cross-modally recognize members of their own taxon. What is unclear is just how plastic this recognition system can be. In this study, we investigate whether an animal, the domestic horse, is capable of spontaneous cross-modal recognition of individuals from a morphologically very different species. We also provide the first insights into how cross-modal identity information is processed by examining whether there are hemispheric biases in this important social skill. In our preferential looking paradigm, subjects were presented with two people and playbacks of their voices to determine whether they were able to match the voice with the person. When presented with familiar handlers subjects could match the specific familiar person with the correct familiar voice. Horses were significantly better at performing the matching task when the congruent person was standing on their right, indicating marked hemispheric specialization (left hemisphere bias) in this ability. These results are the first to demonstrate that cross-modal recognition in animals can extend to individuals from phylogenetically very distant species. They also indicate that processes governed by the left hemisphere are central to the cross-modal matching of visual and auditory information from familiar individuals in a naturalistic setting.     

Replication of four aquatic reoviruses in experimentally infected golden shiners (Notemigonus crysoleucas).

Golden shiners (Notemigonus crysoleucas) experimentally infected with four reoviruses supported replication of golden shiner virus as well as chum salmon virus, reovirus 13p2 and catfish reovirus at temperatures of 23 and 28 C. All four reoviruses replicated in golden shiners in this study. Natural infections of the golden shiner virus are known only in golden shiners.     

The longevity of actinosporean spores from oligochaetes of Lake Sasajewun, Algonquin Park, Ontario, and their reaction to fish mucus

The longevity of 7 forms of actinosporean spores and the reaction of 6 forms of actinosporeans to fish mucus were investigated. The maximum longevity of actinosporean spores kept at ambient laboratory temperatures was 14 days. Spore longevity ranged from 11 to 14 days among actinosporeans. The reaction of spores to fish mucus varied among the actinosporeans. Triactinomyxon F of Xiao and Desser, 1998 reacted only to the mucus of the common shiner Luxilus cornutus, and golden shiner Notemigonus crysoleucas, whereas the aurantiactinomyxon form of Xiao and Desser, 1998, and raabeia B of Xiao and Desser, 1998 reacted readily to mucus of all fish species tested. The differences in reaction to fish mucus among actinosporeans may indicate their different host range. These results indicate that actinosporean spores are short-lived and that actinosporeans respond to their hosts by chemodetection.     

Shape analysis of the jaws between two minnow species over ontogeny

This study compares sand shiner (Notropis stramineus ) and silverjaw (Ericymba buccata ) minnows, in terms of the morphological shape changes of the upper, lower, and pharyngeal jaws over ontogeny. These two species of minnows initially feed on midge larvae and undergo an ontogenic prey shift. The traditional morphometrics measured—total length, snout‐to‐vent length, eye diameter, premaxilla length, lower jaw length, gape—were regressed onto total length to test for allometry. Digital pictures were processed with tpsDig and further analyzed with MorphoJ utilizing a regular geometric morphometrics procedure using principle component analyses. We examined gut contents for 16 fish of each species. For the silverjaw minnows, we found all jaw variables to exhibit positive allometric growth with increasing total length, while most of the jaw variables for the sand shiner exhibited negative allometric growth with increasing total length. This correlates with an ontogenic prey shift for both species. Sand shiner minnows have been found to be more omnivorous, feeding on algae later in life, while silverjaw minnows undergo a prey shift to larger invertebrates. These species lack oral dentition causing an increased reliance on the pharyngeal apparatus. Principle component analyses revealed elongation of pharyngeal jaw elements in the silverjaw minnows and a relative shortening and bulking of pharyngeal jaws in the sand shiner minnows. The ontogenic dietary shifts observed in these two species provide possible explanation for the morphological changes over ontogeny in jaw elements, which are likely enabling these species to occupy the same habitat with little niche overlap.     

Understanding complex reproductive ecology in fishes: the importance of individual and population-scale information

Many riverine cyprinids native to the Great Plains of North America are members of a reproductive guild that broadcast spawns pelagic, semi-buoyant ova. The task of fully understanding and appreciating the complexity of the reproductive ecology of this guild has been difficult. Although various efforts to understand their reproductive ecology have been conducted over the last 60 years, the results of these studies and the conclusions drawn from them have been inconsistent and oftentimes seemingly contradictory. The result has been varied and ill-informed conservation and management strategies based on an incomplete understanding of the reproductive ecology of these fish. We used gonadosomatic index, oocyte development, oocyte size distribution, and histological techniques to assess the reproductive ecology of sharpnose shiner Notropis oxyrhynchus in the upper Brazos River, Texas, between April 2003 and March 2005. Histological analyses of ovarian tissue revealed that reproduction occurred over a six-month period between April and September during which individual fish spawned multiple times. Patterns in gonadosomatic index, oocyte development, and oocyte size distribution indicated that sharpnose shiner spawn asynchronously except during periods of increased streamflow when spawning is synchronized within populations. Reproductive ecology of the sharpnose shiner reported in this study appears to be nearly identical to that recently reported for two other broadcast spawning cyprinids in the Great Plains, indicating that a more complete and consistent understanding of their reproductive ecology is beginning to emerge. We attribute this to the inclusion of both individual and population-scale analyses used in the most recent studies.