Coho Salmon (Oncorhynchus kisutch) Prefer and Are Less Aggressive in Darker Environments

Fish are capable of excellent vision and can be profoundly influenced by the visual properties of their environment. Ambient colours have been found to affect growth, survival, aggression and reproduction, but the effect of background darkness (i.e., the darkness vs. lightness of the background) on preference and aggression has not been evaluated systematically. One-hundred Coho salmon (Oncorhynchus kisutch), a species that is increasing in popularity in aquaculture, were randomly assigned to 10 tanks. Using a Latin-square design, every tank was bisected to allow fish in each tank to choose between all the following colour choices (8 choices in total): black vs. white, light grey, dark grey, and a mixed dark grey/black pattern, as well as industry-standard blue vs. white, light grey, dark grey, and black. Fish showed a strong preference for black backgrounds over all other options (p < 0.01). Across tests, preference strength increased with background darkness (p < 0.0001). Moreover, having darker backgrounds in the environment resulted in less aggressive behaviour throughout the tank (p < 0.0001). These results provide the first evidence that darker tanks are preferred by and decrease aggression in salmonids, which points to the welfare benefits of housing farmed salmon in enclosures containing dark backgrounds.     

ADAPTIVE COLORATION AND GENE FLOW AS A CONSTRAINT TO LOCAL ADAPTATION IN THE STREAMSIDE SALAMANDER,AMBYSTOMA BARBOURI

Predation is an important selective force that influences animal color patterns. Some larval populations of the streamside salamander, Ambystoma barbouri, inhabit streams with fish predators. Other larval salamanders are found in shallow, ephemeral streams that are predator-free. Quantitative melanophore cell counts and estimates of percent body area pigmented indicated that larval coloration is strongly correlated with stream type. Larvae that coexist with fish tend to be lighter than larvae from streams that are Ashless and ephemeral. Two approaches demonstrated that lightly pigmented salamander larvae better match the common background in relatively permanent streams and are less conspicuous to fish than dark larvae. First, using a model based on the spectral sensitivity of the fish and reflectance properties of salamanders and natural stream backgrounds, we showed that light larvae are three times more cryptic than dark larvae on rocks. Second, lighter larvae had higher survival than darker salamanders on rocks in a predator- choice experiment. It is not clear why larvae in ephemeral streams are darker. Larvae in ephemeral streams should be active to feed and develop rapidly and reach sufficient size to metamorphose before seasonal drying. Several hypotheses may explain why larvae tend to be darker in ephemeral streams, such as increased thermoregulatory ability, better screening of ultraviolet radiation (in these shallower streams), or better background matching to terrestrial predators. Among populations where salamander larvae coexist with fish, there are differences in relative crypsis. Larvae from populations with fish and relatively high gene flow from ephemeral populations (where larvae are dark) tend to be darker (with more melanophores) and more conspicuous to predators than those from more genetically isolated populations, where larvae are lighter and more cryptic. These differences illustrate the role of gene flow as a constraint to adaptive evolution.     

Active background choice facilitates crypsis in a tropical crab

Animals can evade predators in multiple ways, one of the most effective of which is to avoid detection in the first place. We know much about the evolution of color patterns that match the visual background to avoid detection (i.e., crypsis), yet we know surprisingly less about the specific behaviors that have co‐evolved with these morphological traits to enhance or maintain crypsis. We here explore whether the match between body color and background in a seemingly well‐camouflaged tropical shore crab is a result of active background choice. Taking advantage of a coastal area in the Solomon Islands with variable sand color and a population of the pallid ghost crab Ocypode pallidula with varying carapace color, we experimentally tested whether individuals actively choose specific substrate that best matches their color patterns. We found that individuals taken from extreme sand colors chose substrate that maintained crypsis, with relatively darker crabs typically choosing dark sand and lighter crabs choosing light sand. Crabs of intermediate color pattern, in contrast, showed no clear preference for dark or light sand. Our results suggest that potential prey can actively choose specific backgrounds to enhance and maintain crypsis, providing insights into how behavior interacts with morphological traits to avoid predator detection.     

The roles of colour change and behaviour in the hygrothermal balance of a littoral isopod,Ligia oceanica

Summary Ligia oceanica can change its colour using melanophores, the animal's reflectance varying between about 2 and 10%. Darker individuals heat up more quickly, and to higher body temperatures, than do pale ones. Colour change shows an underlying circadian rhythm, though the pattern of this rhythm varies with temperature, humidity, background and time of year. In general the rhythm is such as to ensure maximum camouflage at the critical dusk period, but in some conditions hygrothermal needs are overriding and the animals are paler (to stay cool) or darker (to warm up). In addition, animals show short term colour modification; when transferred to differing backgrounds and temperatures their colours initially reflect background matching, but after 30–45 min are modified into thermally appropriate shades, dark at 5° C and pale at 20° C. Field-caught specimens showed body temperatures that varied with colouration, and modification of colour in relation to thermal needs, particularly by being paler than expected when forced into the open by daytime high tides, and darker than expected when active prior to dusk. Animals invariably selected dark backgrounds in choice chambers. However, choice of humidity depended on previous experience; saturated air was normally preferred, but warm animals chose drier air (to allow evaporative cooling) unless also water-stressed. They also tended to disperse to facilitate cooling, whereas aggregation increased with increasing RH and with decreasing temperature. The interactions of colour changes, behavioural choices, and activity patterns in controlling the hygrothermal belance of Ligia in the intertidal environment are discussed in the light of these results.     

Color change and color-dependent behavior in response to predation risk in the salamander sister species<Emphasis Type="Italic"> Ambystoma barbouri</Emphasis> and<Emphasis Type="Italic"> Ambystoma texanum</Emphasis>

Although many organisms show multiple types of trait responses to predation risk (e.g., shifts in behavior, morphology, color, chemistry or life history), relatively few studies have examined how prey integrate these multiple responses. We studied the joint expression of color and behavioral responses to predation risk in two sister species of salamander larvae that live in habitats with different selection pressures. We examined responses to predation risk in three situations that differed in availability of refuge and substrate color heterogeneity, and thus availability of behavioral options for reducing risk. Relative to Ambystoma texanum, A. barbouri larvae were darker in color and showed a greater range of color change. With no variation in background color or refuge available, both species exhibited color change to better match the available background. The degree of color change showed by both species, however, did not depend on predation risk. Given the option to choose between light and dark substrates, A. texanum exhibited behavioral background matching (i.e., they preferred substrates that matched their own body color), while A. barbouri's substrate preferences did not depend on their initial body color. Instead, A. barbouri responded to risk by showing a strong preference for dark substrates, followed by a change to a darker body color. With refuge available, A. texanum's refuge use was color-dependent; larvae that were well camouflaged spent less time in refuge. In contrast, A. barbouri showed strong refuge use in response to risk, regardless of their body color. Overall, these results reflect how conflicting selection pressures (predation risk, habitat ephemerality, risk of UV damage) and species differences in mean color and ability to change color can govern the interplay of complementary and compensatory behavioral and color responses to predation risk.     

Effects of substrate color on intraspecific body color variation in the toad‐headed lizard,Phrynocephalus versicolor

Diversity in animal coloration is generally associated with adaptation to their living habitats, ranging from territorial display and sexual selection to predation or predation avoidance, and thermoregulation. However, the mechanism underlying color variation in toad‐headed Phrynocephalus lizards remains poorly understood. In this study, we investigated the population color variation of Phrynocephalus versicolor. We found that lizards distributed in dark substrate have darker dorsal coloration (melanic lizards) than populations living in light substrates. This characteristic may improve their camouflage effectiveness. A reciprocal substrate translocation experiment was conducted to clarify the potential role of morphological adaptation and physiological plasticity of this variation. Spectrometry technology and digital photography were used to quantify the color variation of the above‐mentioned melanic and nonmelanic P. versicolor populations and their native substrate. Additionally, substrate color preference in both populations was investigated with choice experiments. Our results indicate that the melanic and nonmelanic populations with remarkable habitat color difference were significantly different on measured reflectance, luminance, and RGB values. Twenty‐four hours, 30 days, and 60 days of substrate translocation treatment had little effects on dorsal color change. We also found that melanic lizards choose to live in dark substrate, while nonmelanic lizards have no preference for substrate color. In conclusion, our results support that the dorsal coloration of P. versicolor, associated with substrate color, is likely a morphological adaptation rather than phenotypic plasticity.     

Background choice as an anti-predator strategy: the roles of background matching and visual complexity in the habitat choice of the least killifish

Because background matching improves concealment, prey animals have traditionally been expected to prefer parts of the habitat that match their visual appearance. However, empirical support for this is scarce. Moreover, this idea has recently been challenged by an alternative hypothesis: visual complexity of the background impedes prey detection, and hence prey could instead prefer complex parts of the habitat. We used the least killifish to test, with and without predation threat, for the importance of the visual similarity between the fish and the background, and the level of visual complexity of the background. We observed their choice between backgrounds patterned with elements based on the longitudinal black stripe of the fish. Predation risk was important under some circumstances, and induced a preference for a background of matching horizontal stripes compared with mismatching vertical stripes. Interestingly, females under predation threat showed a preference for a complex background of randomly oriented and overlapping stripes compared with matching stripes, whereas males did not discriminate between these two. Additionally, males showed a preference for matching stripes compared with complex shapes, whereas females did not discriminate between these backgrounds. We conclude that matching is important in the choice for safe habitat, but some aspects of visual complexity may override or act together with background matching.     

Crypsis in a heterogeneous environment: relationships between changeable polymorphic colour patterns and behaviour in a galaxiid fish

1. The ability to achieve optimal camouflage varies between microhabitats in heterogeneous environments, potentially restricting individuals to a single habitat or imposing a compromise on crypsis to match several habitats. However, animals may exhibit morphological and behavioural attributes that enhance crypsis in different habitats. 2. We used an undescribed fish species, Galaxias‘nebula’, to investigate two objectives. First, we examined two potential methods of enhancing crypsis: change in colour pattern and selection of a suitable background. Second, we characterised the colour pattern of this unstudied fish and assessed its capacity for crypsis. 3. No background selection was apparent but the area of dark pigment expressed varied between backgrounds, which may negate the requirement to be choosy about habitats. The capacity to change colour and selection of a background that maximises crypsis are most likely separate, non‐mutually exclusive strategies. 4. Galaxias‘nebula’ exhibits polymorphic, non‐interchangeable colour patterns that have elements of both background pattern matching and disruptive colouration. This, coupled with habitat characteristics, suggests a combination of generalist and specialist strategies of habitat use. The fish’s camouflage strategy and air‐breathing ability may be key to survival under increasing pressure from habitat degradation and invasive predators.     

Colour preference and potato cultivar oviposition choice by onion thrips,Thrips tabaci (Thysanoptera: Thripidae)

Thrips tabaci (Lindeman) is an important polyphagous pest, and vector of Tomato spotted wilt virus responsible for sporadic, but devastating epidemics in potato. T. tabaci shows significant preferential differences between potato cultivars that may be important for field resistance. To investigate the role of visual cues in host choice we tested colour preference using two-choice assays. Thrips tabaci showed a significant preference for mid-green over red, blue, and white coloured cards, a preference for both light-green and mid-green over dark-green, and light-green over yellow, but no preferential difference between mid-green and yellow, and between light-green and mid-green. Analysis of the spectral reflectance of potato cultivars differing in thrips preference, revealed significant differences within the 400–700 nm wavelengths. In most cases cultivars preferred by T. tabaci had lighter green foliage and higher reflectance at 552 nm, and thus colour preference may be important for host selection. Oviposition choice of T. tabaci for potato cultivars was determined from counts of larvae and unhatched eggs from leaf disks under choice and no-choice conditions. In contrast to the colour choice experiments, onion thrips showed oviposition preference for cultivars with darker green foliage and lower reflectance at 552 nm.     

Phenotypic plasticity in a generalist insect herbivore with the combined use of direct and indirect cues

Ultimate causes of phenotypic plasticity in visual appearance are frequently related to increasing the degree of crypsis in a way specific to the environment. The cues used to elicit such plastic responses may be both direct (i.e. straightforward background matching) as well as indirect. In the latter case, cues other than the visual signals from of the environment are used to predict the phenotype best corresponding to the particular situation. On the basis of a series of laboratory experiments we show that the remarkable variability in the visual appearance of the larvae of the geometrid moth Ematurga atomaria, though genetically based in part, involves a substantial environmental component. Using multiple correspondence analysis, we transformed the multidimensional variation in colour and pattern into two dimensions interpretable as patterning and darkness. Plastic changes in the darkness of the larvae were elicited by direct cues: the larvae were darker when reared on dark host‐plants. Host‐specific degree of patterning was also induced in absolute darkness which indicates the use of an indirect cue. This was unexpected because the study species is broadly polyphagous, and thus not likely to have evolved adaptations specific to particular host‐plant species. Indeed, the larvae of E. atomaria originating from geographic populations using different host‐plants showed analogous plastic responses which indicates that the link between the indirect cue and visual appearance of the host needs not to be specific to plant species. In an additional experiment, we showed that surface roughness is a likely candidate to serve as the proximate cue for determination of some pattern elements, a case not reported for insect larvae earlier.     

Common Wall Lizard Females (Podarcis muralis) do not Actively Choose Males Based on their Colour Morph

Identifying the processes that lead to the evolution and maintenance of links between colour morphs and behavioural strategies has implications for the evolution of reproductive isolation and sympatric speciation. Sexual selection may play a significant role in the evolution of colour pattern complexity in reptiles, particularly when there are fitness consequences associated with mating with males of different colour morphs. In this article, we explored if common wall lizard females (Podarcis muralis) actively select males according to their morph in a colour‐assortative pattern using a multiple‐choice experiment with both visual and chemical cues. We failed to identify female active mate choice, as females did not choose males based on male colouration or femoral pore secretions. Indeed, females equally entered the three preference compartments and spent nearly the same amount of time within them, irrespective of both colour and odour of males. Consequently, our results do not support the hypothesis that colour polymorphism in this species may be driven by colour‐assortative mating promoted by females. However, we cannot exclude the possibility that females may choose males according to their colour following a flexible choice strategy, nor the possibility that females actively discriminate among males according to qualities that are not directly related to morph‐specific strategies.     

Fruit Colour Preferences of Redwings (Turdus iliacus): Experiments with Hand-Raised Juveniles and Wild-Caught Adults

Certain fruit colours and their contrast with the background coloration are suggested to attract frugivorous birds. To test the attractiveness of different colours, we performed three experiments in laboratory with controlled light conditions. In the first two experiments, we studied the fruit colour preferences of naive juvenile redwings. In the third experiment, we continued to investigate whether the contrast of the fruit colour with the background coloration affects the preference of both naive juveniles and experienced adult redwings. In the first experiment, juvenile birds preferred black, UV‐blue and red berries, to white ones. In pairwise trials, a new set of juveniles still preferred red berries to white ones. When testing the effect of contrasts on their choice, juveniles preferred UV‐blue berries to red ones on a UV‐blue background. However, no preference was found, when the background was either red or green. Adult redwings preferred UV‐blue berries to red ones on all backgrounds. According to these results, juveniles seem to have an innate avoidance of white berries. Furthermore, the foraging decisions of fruit‐eating birds are affected more by fruit colour than its contrast with background coloration, at least when contrasting displays are encountered from relatively short distances. Differences in preferences of adult and juvenile birds also indicate that learning seems to play a role in fruit choices.     

Can snakes hide in plain view? Chromatic and achromatic crypsis of two colour forms of the Western Terrestrial Garter Snake (Thamnophis elegans)

Colours influence numerous aspects of an animal's ecology. One possibility is that colour helps make an animal cryptic against the background on which it is resting. We test this hypothesis for two different, geographically separated colour forms (dark forms and light forms) of the Western Terrestrial Garter Snake, Thamnophis elegans. We quantified crypsis of snakes, in terms of colour (chromatic crypsis) and brightness (achromatic crypsis), by using objective measures of spectral reflectance of snakes and the surrounding habitat. These data were visually modelled from the perspective of potential snake predators and human researchers. Overall, snakes of both colour forms selected basking sites that increased chromatic crypsis over that which would have been achievable on random backgrounds. Both colour forms of T. elegans appear to exhibit similar achromatic and chromatic crypsis when viewed by potential predators, such as mammals and birds. From the perspective of the human visual model, dark T. elegans were generally more chromatically cryptic than light T. elegans, contrary to our a priori subjective impression. The main contribution of the present study is that we provide one of the first objective comparisons of snakes and their backgrounds as a measure of crypsis. Although we found some evidence for crypsis as a factor in choice of basking sites for snakes, other factors (e.g. thermoregulatory opportunities) undoubtedly play important roles as well. We also have not addressed whether snakes involved in other activities are cryptic or whether there are differences between the sexes or between reproductive and nonreproductive females. The adaptive significance of colour variation has been studied in diverse taxonomic groups. Although the mechanisms are not straightforward, the opportunities to carry out further work in this area are enhanced by the availability of objective approaches. © 2013 The Linnean Society of London,     

Rockpool Gobies Change Colour for Camouflage

Camouflage is found in a wide range of species living in numerous habitat types, offering protection from visually guided predators. This includes many species from the intertidal zone, which must cope with background types diverse in appearance and with multiple predator groups foraging at high and low tide. Many animals are capable of either relatively slow (hours, days, weeks) or rapid (seconds and minutes) colour change in order to better resemble the background against which they are found, but most work has been restricted to a few species or taxa. It is often suggested that many small intertidal fish are capable of colour change for camouflage, yet little experimental work has addressed this. Here, we test rock gobies (Gobius paganellus) for colour change abilities, and whether they can tune their appearance to match the background. In two experiments, we place gobies on backgrounds of different brightness (black or white), and of different colours (red and blue) and use digital image analysis and modelling of predator (avian) vision to quantify colour and luminance (perceived lightness) changes and camouflage. We find that gobies are capable of rapid colour change (occurring within one minute), and that they can change their luminance on lighter or darker backgrounds. When presented on backgrounds of different colours, gobies also change their colour (hue and saturation) while keeping luminance the same. These changes lead to predicted improvements in camouflage match to the background. Our study shows that small rockpool fish are capable of rapid visual change for concealment, and that this may be an important mechanism in many species to avoid predation, especially in complex heterogeneous environments.     

Fonction chromatrope de la pars intercerebralis chez l'acridien Oedipoda coerulescens

The median neurosecretory cells of the protocerebrum of fifth instar larvae and 1- or 2-day-old adults of Oedipoda coerulescens produced more fuchsinophilic material when reared on dark backgrounds than on pale ones. In the latter case, the neurosecretory cell bodies were almost completely devoid of neurosecretion. The same differences were found in the anterior lobes of the corpora cardiaca. Individuals implanted with pars intercerebralis from donors reared on a dark background showed dark pigmentation no matter what their own background colour (and conversely). Black or red pigmentation appeared on absorbent grounds whereas a pale one was produced on reflecting grounds with high levels of incident light predominantly between 576 and 588 mμ. The significance of these results is discussed. A possible scheme for the interaction of environmental factors and pigmentation is suggested.     

RESEARCH PAPER: Multiple Sexual Ornamentation Signals Male Quality and Predicts Female Preference in Minnows

Sexual ornamentation often consists of multiple components. Different sexual signals may indicate different aspects of mate quality or reflect quality in different time scales. On the other hand, same signals can have a dual function and are used both in male–male competition and courtship. Many fish species are capable of rapidly altering their colouration (ephemeral colour changes), but this capability is usually ignored in sexual selection studies. Here, we used experimentally manipulated social environments to study the ephemeral colour changes in multicomponent sexual signals of male minnows (Phoxinus phoxinus) during male–male competition and female choice. We found that the dominant males courted the females more actively and had redder and/or darker skin colouration than the subordinate males. Furthermore, darkness difference between subordinate and dominant males increased in the presence of female, which suggests that the male–male competition may increase the honesty of signalling and thus facilitate female choice. In support of this hypothesis, females had a strong behavioural preference towards the more colourful males, which may indicate female choice. As colourful males often had a higher social status than paler individuals, it is possible that females base their preference on male status, not only the colouration per se. In any case, our results suggest that sexual ornamentation of male minnows may signal status, courting activity and superior quality of the males and that these signals may have a dual function in both male–male competition and female choice. Females preferred different ornamental traits (dark and red colour patterns) relatively equally, indicating that mate choice is based on multiple cues.     

Sphagnum mosses as a microhabitat for invertebrates in acidified lakes and the colour adaptation and substrate preference in Leucorrhinia dubia (Odonata, Anisoptera)

The increase of peat mosses. Sphagnum spp, in acidified lakes leads to a changed microhabitat structure for benthic invertebrates The importance of this change was investigated for some benthic invertebrates Comparisons between quantitative samples of Sphagnum and debris within the acidified Lake Stora Hastevatten, in the Lake Gårdsjon catchment of SW Sweden, showed significantly higher abundances of Chironomidae, Ceratopogonidae, Odonata, Trichoptera, Cladocera and Argyroneta aquatica (Araneae) in Sphagnum For Chironomidae and Cladocera the differences were tenfold Special reference was made to the libellulid Leucorrhinia dubia which is common in acid lakes In a laboratory test, late instar larvae of L dubia were shown to be able to change colour to correspond to the brown and green colour of Sphagnum This result was completed with a field test where larvae of L dubia were significantly more common in Sphagnum of the same colour as the larvae The ability to change colour may have an adaptive value when coexisting with visual predators Small larvae, 4-5 mm, were significantly more prevalent in Sphagnum and they also showed significant preference for this substrate in the laboratory test For medium-sized larvae, 12-14 mm, a tendency to prefer Sphagnum was found in the laboratory test Larvae of L dubia were shown to be more successful as predators on Asellus aquaticus in Sphagnum substrate than in debris in the laboratory test Laboratory predation tests with Notonecta glauca, Corixa dentipes, Acilius sulcatus, Hyphydrus ovatus and L dubia showed that they could all feed on larvae of L dubia The complex habitat structure of Sphagnum is probably the reason for the high abundance of invertebrates since it may serve as both shelter against predation and as foraging sites It is probably important as a key habitat for young instars of, for example, L dubia In lakes with large Sphagnum mats, L dubia can coexist with fish The expansion of Sphagnum due to acidification will probably benefit many acid-tolerant invertebrate species     

Threshold determination for olfactory receptors of the spiny lobster

The shallow water caridean shrimps Heptacarpus pictus and H. paludicola are polymorphic in colour pattern. Populations of these species collected over colour‐variable substrates showed the greatest degree of coloration in terms of the proportion of individuals displaying a distinct colour pattern. The frequencies of H. Pictus colour morphs varied significantly between most sampling periods. Apostatic selection by fish predators is suggested as one hypothesis which could explain these changes in morph frequency.

Experiments with Heptacarpus pictus on rapid colour change showed that, although some pigment migration did occur in the chromatosomes studied, the macroscopic appearance of the colour patterns was not altered when shrimps were shifted from black to white backgrounds or vice versa. The results of background choice experiments with H. pictus suggest that these shrimp do not seek out colour backgrounds that would seem to be a matching background in a concealing coloration. This behaviour is consistent with the morphology of the colour patterns which appears to be a disruptive coloration rather than a concealing coloration that closely matches a particular substrate.     

Influence of previous experience on the mate selection of two colour morphs of the convict cichlid, Cichlasoma nigrofasciatum (Pisces,Cichlidae)

In a pilot test, individuals of two colour morphs of Cichlasoma nigrofasciatum showed colour preferences in their schooling behaviour according to previous experience. Two further experiments were undertaken to investigate if such experientially induced preferences could reflect on the choice of mate. In one experiment white males who had been reared differently with regard to the colour morph of parents and siblings were given females of the different colour morphs (white and normal) to choose from, the females being successively removed after pairing to induce further choices. In this test, however, the males predominantly chose normal females, probably because of dominance relationships among the females, which masked a possible colour preference. Instead, a free choice test was devised, where 74 white and 74 normal fishes were allowed to pair off freely in a large tank. Here, a statistically significant sexual preference for the previously experienced colour morph was found. These results, as well as the possible evolutionary consequences, are discussed.     

Habitat choice and recruitment of tropical fishes on temperate coasts of Japan

Tropical reef corals are expanding on Japanese temperate coasts in response to rising sea surface temperatures, and many tropical fish juveniles have been observed routinely in these coral habitats. The present study explored how offshore tropical fish larvae locate coral habitat on the temperate coasts of Japan. Settlement-stage larvae were sampled between July and October 2009–2011 with light traps anchored on coral-replete and coral-free habitats (rocky habitats) at two-level distance (distance between each habitat type was 6 km and 500 m, respectively). Larval abundance was significantly higher on the coral-dominated habitat than that on the rocky habitat at both short and long distance sites, suggesting that coral habitats attract offshore tropical fish larvae. In underwater visual survey, Chaetodontidae and Pomacentridae juveniles were more abundant in coral habitats than in rocky habitats at both the sites, and a laboratory habitat choice experiment demonstrated that these larvae showed a preference for corals rather than rocks. In contrast, densities of juvenile Mullidae did not differ between the coral and rocky habitats, and the larvae did not show a substrate preference in the habitat choice experiment. These observations suggest that habitat choice at settlement possibly accounts for the differences in settlement patterns of tropical fishes between the two habitats. Taken together, our results showed that most tropical fish larvae colonize their settlement coast at a scale of ~0.5 km, and that they may locate coral habitats after reaching a reef. Moreover, the results suggest that coral habitat expansion on temperate coasts will lead to an increase in coral-associated tropical fishes and will change assemblage structures of fishes on temperate coasts.