Shut up or shout loudly: Predation threat and sound production in fishes

Predation is a major ecological constraint shaping behaviour and communication in animals. Several fish species are known to modify their foraging, agonistic and reproductive behaviour in the presence of predators. However, close to nothing is known about how predators affect sound production in fishes. This paper reviews how vocal fish increase their chance of survival by modifying intraspecific acoustic communication and by producing sounds directed towards predators. Field studies showed that toadfish, drums and squirrelfish reduced the number and loudness of calls when dolphin sounds were played back. These studies lack behavioural observations, leaving the question open how individual fish respond to predation threat. Croaking gouramis (Trichopsis vittata, Osphronemidae) reduced acoustic and visual signalling during dyadic contests and refrained from escalated behaviour when detecting a predator in an adjacent tank. This indicates that gouramis increase their vigilance by reducing agonistic behaviour. Vocal fish have been observed to emit sounds when predators approach or when being caught. However, none of the predators (or even conspecifics nearby) responded to these calls. Therefore, the term “predator-related” sound has been introduced in this paper to avoid implying unproven functions (alarm, startling, warning, distress and disturbance). Interestingly, the readiness of numerous taxa (e.g. catfishes) to vocalize when hand-held or netted was frequently exploited to investigate sound production in fish in relation to weight, sex, sonic organs, temperature or phylogeny. Increasing levels of noise in aquatic habitats call for more research on predator–prey interactions because of potential negative effects on detection of sounds produced by predators or prey.     

Acoustic communication in fishes: Temperature plays a role

Temperature affects peripheral and central mechanisms of signal production and detection in ectothermic animals. This study reviews for the first time the effects of temperature on acoustic communication in fishes and analyses whether changes in sound properties are coupled to changes in auditory sensitivities. Effects of temperature on sound production have been studied in approximately one dozen families of teleosts. Calling activity increased or was unaffected by temperature, in the latter case probably because seasonal, daily and lunar rhythms also influence mating behaviour and calling. Sound characteristics (pulse repetition rate, fundamental frequency) are positively correlated with temperature if pulses are directly based on sonic muscle contractions. In fishes possessing other sonic mechanisms, the dominant frequency of their pulsatile pectoral sounds may increase as well. Auditory sensitivities were mainly determined in otophysines, which possess enhanced hearing abilities. Studies revealed that hearing increased with temperature, in particular at higher frequencies. We know close to nothing about whether temperature‐dependent changes in sound characteristics are coupled to changes in auditory sensitivity or mate choice. Female midshipman toadfish appear to choose males based on call frequency, which varies with temperature. Future studies need to address several topics: (i) temperature effects on sound production have to be separated from other sources of variation; (ii) effects on hearing need to be studied in many more taxa; (iii) potential negative effects of global warming on acoustic communication (because of temperature coupling) need to be investigated because fish constitute a major source of protein for humans.     

Population‐level consequences of seismic surveys on fishes: An interdisciplinary challenge

Offshore activities elevate ambient sound levels at sea, which may affect marine fauna. We reviewed the literature about impact of airgun acoustic exposure on fish in terms of damage, disturbance and detection and explored the nature of impact assessment at population level. We provided a conceptual framework for how to address this interdisciplinary challenge, and we listed potential tools for investigation. We focused on limitations in data currently available, and we stressed the potential benefits from cross‐species comparisons. Well‐replicated and controlled studies do not exist for hearing thresholds and dose–response curves for airgun acoustic exposure. We especially lack insight into behavioural changes for free‐ranging fish to actual seismic surveys and on lasting effects of behavioural changes in terms of time and energy budgets, missed feeding or mating opportunities, decreased performance in predator‐prey interactions, and chronic stress effects on growth, development and reproduction. We also lack insight into whether any of these effects could have population‐level consequences. General “population consequences of acoustic disturbance” (PCAD) models have been developed for marine mammals, but there has been little progress so far in other taxa. The acoustic world of fishes is quite different from human perception and imagination as fish perceive particle motion and sound pressure. Progress is therefore also required in understanding the nature and extent to which fishes extract acoustic information from their environment. We addressed the challenges and opportunities for upscaling individual impact to the population, community and ecosystem level and provided a guide to critical gaps in our knowledge.     

玻璃钢水槽内大黄鱼养殖环境噪声测量与分析

利用水下声音测量系统,分别记录了开放式圆形玻璃钢水槽内养殖环境噪声和大黄鱼(Larimichthys crocea)摄食过程声音,并进行声压级(sound pressure levels,SPL)计算和频谱特征分析。结果表明:(1)养殖环境噪声SPL约为110.27 d B(d B re:1μPa),包括主频率峰值为100 Hz的养殖工作设备与水槽内壁的低频共振噪声、1 250 Hz的表层水体气泡噪声、1 600~2 500 Hz的曝气石、增氧机、空气压缩机工作噪声;(2)增氧机和曝气关闭时,大黄鱼摄食过程声音SPL约为92.65 d B,高于背景噪声SPL,主要为游泳声音70~500Hz、吞食产生的水体表面搅动与气泡破裂的声音1 000~2 000 Hz、咀嚼颗粒饵料声音2 000~4 500 Hz;(3)增氧机和曝气开启时,背景噪声SPL略高于摄食声音约17.62 d B,且摄食声音无法区别于背景噪声,但并未影响鱼类摄食行为。     

Spatial avoidance of tu‐fish Schizopygopsis younghusbandi for different sounds may inform behavioural deterrence strategies

Water diversions for hydropower and other applications can potentially affect wild fish populations. Although some evidence indicates that acoustic barriers can prevent fish from entrainment into such infrastructures, few studies have been conducted on filtering candidate sound stimuli. Here, the effectiveness of three types of sounds acting as acoustic barriers to prohibit the movement of tu‐fish Schizopygopsis younghusbandi (Regan) was evaluated. The phonotaxic response of the fish to recordings of hissing sound (sound of Chinese alligator Alligator sinensis hissing), outboard motorboat and pile driving noise, compared to control conditions (recordings of ambient riverine noise), was investigated using playback approaches in a fibreglass tank. The tu‐fish reacted to the hissing sound at relatively low sound intensity by exhibiting negative phonotaxis with significantly more responses (F_3,79 = 49.590, p < 0.01) and faster swimming (F_3,219 = 310.086, p < 0.01) away from the sound source during the 10‐min trials than to control conditions. However, the fish were relatively impervious to the outboard motorboat and pile driving noise even when the sound intensities were increased. These results indicate that the potential use of the hissing sound to manipulate fish behaviour and to help protect them from water diversion structures.     

He leaps,she beats: The role of social interactions on the overland movements of an Amazonian amphibious killifish

Amphibious habits are present in a variety of fish and are allowed by a set of physiological, morphological and behavioural adaptations. The most intriguing question, however, is what motivates an aquatic organism to venture into the land? Unfavourable abiotic and biotic conditions in the aquatic environment have been reported as main stimuli for fish to emerge from water. However, few attempts have been made to disentangle the effects of different social contexts on the propensity of amphibious fishes to leave the water. Trying to separate the effects of predator threat, intraspecific competition and mate searching on overland movement of amphibious fish, we ran a mesocosm experiment with the Amazonian killifish Anablepsoides micropus. Overland movement was quantified based on fish leaps between artificial pools set in enclosures in a primary forest area. Males moved overland more frequently than females and their movement depended on the social context, being higher in the presence of predators and lower in the presence of females. Females, instead, showed context‐independent movement rates. This suggests that males move between pools searching for mates, stopping when successful in this search. On the other hand, occasional encounters with predators may force males to abandon the pool as a defence mechanism. Female aggressiveness towards the predator may influence its low movement in the presence of the predator. Such differential responses may play important ecological and evolutionary roles, allowing A. micropus to occupy a wide range of environmental conditions under varied ecological and social contexts.     

Predator and prey events at the entrance of a surface-oriented fish collector at North Fork Dam,Oregon

Quantifiable estimates of predator–prey interactions and relationships in aquatic habitats are difficult to obtain and rare, especially when individuals cannot be readily observed. To overcome this observational impediment, imaging sonar was used to assess the cooccurrence of predator-size fish and juvenile salmonids, Oncorhynchus spp., at the entrance to a floating surface collector (FSC) in the forebay of North Fork Dam on the Clackamas River, Oregon (USA). Imaging sonar can be used to transform active sound waves into visual data, making it possible to obtain continuous underwater observations on the presence and interspecific interactions between predator-size fish and prey (juvenile salmonids). Hourly counts of smolt-size fish tracks, diel phase, water clarity and river discharge were used as covariates within a zero-inflated Poisson model to determine how these factors may influence the number of predators in front of the FSC. Both the number of smolt-size fish tracks and diel phase had the strongest effects on the number of predator-size fish tracks, with more predator-size fish tracks observed during the daytime, and as the number of smolt-size fish tracks increased. Additionally, the presence of predator-size fish may affect the abundance and direction of travel of juvenile salmonids, as fewer smolt-size fish were observed when predators were present, and a greater proportion of smolt-size fish were observed travelling away from the FSC when predator-size fish were present. This study provides estimates of predator and prey fish abundance in the vicinity of surface collection systems at moderate-sized hydropower projects and could help resource managers better understand mechanisms that can influence the survival and passage behaviour of juvenile salmonids using surface collection structures at dams.     

Spotlined sardine Sardinops melanostictus listensto 1-kHz sound by using its gas bladder

ABSTRACT:   The auditory characteristics of pelagic fish have received lessattention compared to those of benthic or freshwater fish species,even though underwater sounds are considered to affect their behavior.Audiograms of five spotlined sardines were obtained using the auditorybrainstem response technique in which the evoked potential on theskin covering the head of the fish was measured. The auditory brainstemresponse is a non-invasive electrophysiological method that enablesthe auditory threshold level of fragile species, such as spotlinedsardines, to be measured. The gas bladder of the spotlined sardinehas been considered as possibly contributing to an enhancement intheir hearing. In the test, the sound absorption profile of sardineswas also measured. The frequency at the lowest auditory thresholdlevel (i.e. the most sensitive frequency) and absorption were foundat 1024 Hz and 1040 Hz, respectively. The spotlinedsardine was found to be sensitive to sounds at relatively higherfrequency ranges compared to other seawater fishes and the gas bladderis seen to play a significant role in detecting sound.     

草鱼敏感的负趋音筛选

声学屏障是一种阻拦鱼类进入危险区域进而保护鱼类资源的重要手段,为筛选鱼类敏感的负趋音作为声学屏障,本研究采用6种单频音 (500~3 000 Hz)和1种宽频音 (扬子鳄吼叫声)作为实验用音对草鱼幼鱼进行负趋音的筛选研究,通过在水槽两端交替播音来对比草鱼幼鱼对不同声音的行为反应。结果显示,大多数实验鱼对声音有反应,扬子鳄吼叫声与其他声音组的差异显著。单频音实验组中播放500 Hz单频音时平均反应次数最大,为 (1.7±0.6)次,而播放扬子鳄吼叫声时平均反应次数高达 (5.0±0.9)次,显著高于其他实验音。在总平均速度中,宽频音组中草鱼的总平均速度显著高于其他组,表明草鱼对扬子鳄吼叫声敏感,产生逃窜行为。研究表明,草鱼对扬子鳄吼叫声具有负趋音性,扬子鳄吼叫声是一种对草鱼具有驱赶、威慑作用的声音。本研究可为过鱼设施中辅助诱驱鱼手段及水利结构中避免鱼类的夹带提供参考依据。     

Ecological processes influencing mortality of juvenile pink salmon (Oncorhynchus gorbuscha) in Prince William Sound,Alaska

Our collaborative work focused on understanding the system of mechanisms influencing the mortality of juvenile pink salmon (Oncorhynchus gorbuscha) in Prince William Sound, Alaska. Coordinated field studies, data analysis and numerical modelling projects were used to identify and explain the mechanisms and their roles in juvenile mortality. In particular, project studies addressed the identification of major fish and bird predators consuming juvenile salmon and the evaluation of three hypotheses linking these losses to (i) alternative prey for predators (prey‐switching hypothesis); (ii) salmon foraging behaviour (refuge‐dispersion hypothesis); and (iii) salmon size and growth (size‐refuge hypothesis). Two facultative planktivorous fishes, Pacific herring (Clupea pallasi) and walleye pollock (Theragra chalcogramma), probably consumed the most juvenile pink salmon each year, although other gadids were also important. Our prey‐switching hypothesis was supported by data indicating that herring and pollock switched to alternative nekton prey, including juvenile salmon, when the biomass of large copepods declined below about 0.2 g m^?3. Model simulations were consistent with these findings, but simulations suggested that a June pteropod bloom also sheltered juvenile salmon from predation. Our refuge‐dispersion hypothesis was supported by data indicating a five‐fold increase in predation losses of juvenile salmon when salmon dispersed from nearshore habitats as the biomass of large copepods declined. Our size‐refuge hypothesis was supported by data indicating that size‐ and growth‐dependent vulnerabilities of salmon to predators were a function of predator and prey sizes and the timing of predation events. Our model simulations offered support for the efficacy of representing ecological processes affecting juvenile fishes as systems of coupled evolution equations representing both spatial distribution and physiological status. Simulations wherein model dimensionality was limited through construction of composite trophic groups reproduced the dominant patterns in salmon survival data. In our study, these composite trophic groups were six key zooplankton taxonomic groups, two categories of adult pelagic fishes, and from six to 12 groups for tagged hatchery‐reared juvenile salmon. Model simulations also suggested the importance of salmon density and predator size as important factors modifying the predation process.     

Passive monitoring of phenological acoustic patterns reveals the sound of the camouflage grouper,Epinephelus polyphekadion

1. Passive acoustic monitoring (PAM) is a non‐invasive technique that uses hydrophones to monitor populations and ecosystem dynamics. Although many applications of PAM have been developed in recent years, it has never been used to identify a calling marine species.
2. The south pass of Fakarava Atoll, French Polynesia, hosts spawning events of many reef fish species, including the camouflage grouper Epinephelus polyphekadion, with a spawning aggregation abundance exceeding 17 000 individuals during the full moons of June and July.
3. The current study aimed to use PAM to distinguish camouflage grouper sounds among the vocal activities of all fish recorded during the aggregation periods. Audio recordings analysis resulted in the identification of 29 sound types, some of which showed diel and lunar patterns.
4. Temporal analysis of these sounds in relation to spawning activities allowed the identification of camouflage grouper calls. These calls can be described as a single pulse or a series of ‘boom(s)’ with a pulse duration of ~44 ms and a low dominant frequency of 103 ± 31 Hz. Video recordings show that the camouflage grouper produces the ‘booms’ to initialize spawner ascent and to promote synchronous gamete release into the water column.
5. The study highlights for the first time that PAM can be used to identify the previously unknown sound of a fish species. Moreover, we can use it to understand the phenology of some biological activities for improving the resolution of fish biodiversity assessments.

     

草鱼敏感的负趋音筛选研究

声学屏障是一种阻拦鱼类进入危险区域进而保护鱼类资源的重要手段,为筛选鱼类敏感的负趋音作为声学屏障,本文采用六种单频音（500-3 000 Hz）和一种宽频音（短吻鳄吼叫声）作为实验用音对草鱼幼鱼进行负趋音的筛选研究,通过在水槽两端交替播音来对比草鱼幼鱼对不同声音的行为反应。结果表明,大多数实验鱼对声音有反应,短吻鳄吼叫声与其他声音组的差异显著。单频音实验组中播放500 Hz单频音时平均反应次数最大,为1.7±0.6次,而播放短吻鳄吼叫声时平均反应次数高达5±0.9次,显著高于其他实验音;在总平均速度中,宽频音组中草鱼的总平均速度显著高于其他组,表明草鱼对短吻鳄吼叫声敏感,产生逃窜行为。本研究表明,草鱼对短吻鳄吼叫声具有负趋音性,短吻鳄吼叫声可能是一种对草鱼具有驱赶、威慑作用的声音,本研究可为过鱼设施中辅助诱驱鱼手段及水利结构中避免鱼类的夹带提供参考依据。     

Cichlids respond to conspecific sounds but females exhibit no phonotaxis without the presence of live males

Many fish species are able to produce sounds, which are often associated with courtship. In an earlier study, we showed for the Lake Victoria cichlid Pundamilia nyererei that females prefer to associate with a male with sound over a male without sound. As a follow‐up to this earlier finding, we here investigated whether playback of conspecific sounds is sufficient to attract females in the absence of a conspecific male. However, we did not find a phonotactic response for conspecific sounds in the absence of live males, using the same playback procedure as in our previous study. An additional playback test showed that both males and females discriminated between conspecific sounds and bursts of white noise. This suggests that the sounds may be recognised but that they seem only effective as attractant in the presence of visual and/or olfactory cues. These findings underline the multimodal complexity of fish communication and courtship and call for a more integrated study of the different modalities in future studies.     

Do postlarval amphidromous fishes transport marine‐derived nutrients and pollutants to Caribbean streams?

Diadromous fishes are known biotransport vectors that can move nutrients, energy and contaminants in an upstream direction in lotic ecosystems. This function has been demonstrated repeatedly in anadromous salmonids, but the role of other diadromous species, especially tropical taxa, as biotransport vectors is less studied. Amphidromous fish species exhibit potential to act as upstream vectors of nutrients and contaminants in their postlarval and juvenile stages, but this role is largely unknown because of limited understanding of larval growth habitats. Moreover, because some species are harvested in artisanal fisheries as postlarvae, and postlarvae are consumed by riverine and estuarine predators, heavy contaminant loads may present a human or wildlife health concern. This research incorporates stable isotope and contaminant analyses to infer larval habitats and contaminant accumulation of amphidromous fishes on the Caribbean island of Puerto Rico. The isotopic signatures of postlarval amphidromous fishes indicated marine basal sources and food web components, rather than those from riverine habitats. Additionally, postlarvae did not contain concentrations of anthropogenic pollutants that would be of ecological or human health concern. These findings are the first and strongest evidence that amphidromous fish postlarvae function as biotransport vectors of marine nutrients into and up river ecosystems without posing a health threat to the receiving food web or human consumers.     

Hearing in catfishes: 200 years of research

Ernst Weber stated in 1819, based on dissections, that the swimbladder in the European wels (Silurus glanis, Siluridae) and related cyprinids serves as an eardrum and that the ossicles connecting it to the inner ear function as hearing ossicles similar to mammals. In the early 20th century, K. von Frisch showed experimentally that catfishes and cyprinids (otophysines) indeed hear excellently compared to fish taxa lacking auxiliary hearing structures (ossicles, eardrums). Knowledge on hearing in catfishes progressed in particular in the 21st century. Currently, hearing abilities (audiograms) are known in 28 species out of 13 families. Recent ontogenetic and comparative studies revealed that the ability to detect sounds of low-level and high frequencies (4–6 kHz) depends on the development of Weberian ossicles. Species with a higher number of ossicles and larger bladders hear better at higher frequencies (>1 kHz). Hearing sensitivities are furthermore affected by ecological factors. Rising temperatures increase, whereas various noise regimes decrease hearing. Exposure to high-noise levels (>150 dB) for hours result in temporary thresholds shifts (TTS) and recovery of hearing after several days. Low-noise levels reduce hearing abilities due to masking without a TTS. Furthermore, auditory evoked potential (AEP) experiments reveal that the temporal patterns of fish-produced pulsed stridulation and drumming sounds are represented in their auditory pathways, indicating that catfishes are able to extract important information for acoustic communication. Further research should concentrate on inner ears to determine whether the diversity in swimbladders and ossicles is paralleled in the inner ear fine structure.     

Sound features and vocal rhythms as a proxy for locating the spawning ground of Sciaena umbra in the wild

• 1. The brown meagre (Sciaena umbra) is a demersal sciaenid fish recognized as indicative of good environmental quality and is defined as an umbrella species for the ecological community of rocky coastal habitats. Sciaena umbra is classified as a Vulnerable fish species by the International Union for Conservation of Nature (IUCN) and knowledge on the distribution of its spawning habitats is essential for its conservation.
• 2. Passive acoustic monitoring (PAM) is a suitable tool to monitor S. umbra distribution because of the high consistency, over space and time, of the communication sounds that this species emits during the reproductive period, with irregular or regular rhythms, or with calls merging into a chorus.
• 3. During the summer of 2019, the presence of this species was investigated acoustically at 40 listening points distributed along the tidal inlets that connect the Venice lagoon with the open sea.
• 4. Longer sounds, comprising a higher number of faster repeated pulses, were found during the chorus and were used as a proxy of spawning activity; similar sound features have been recorded in different captive Sciaenids during spawning.
• 5. The three inlets were classified as more or less suitable for spawning on the basis of the vocal rhythms identified, demonstrating a clear preference along a north–south gradient and indicating higher spawning activity in the internal‐facing areas of the inlets, compared with the seaward‐facing areas. The chorus occurred in localized areas consistently throughout the breeding season, suggesting that spawning is concentrated in preferred areas.
• 6. For the first time a relationship between the sound features and vocal rhythms of fish has been highlighted by an in situ study. This validates the use of the chorus as a reliable natural indicator of S. umbra breeding sites, and in turn suggests a potential non‐invasive approach based on PAM for mapping the key reproductive areas of this vulnerable species in the Mediterranean Sea.

     

噪声对鱼类影响研究现状与展望

本文对国内外学者就噪声对鱼类听力、信息掩蔽、生理和行为等多方面的研究成果进行了总结，为噪声对鱼类的影响提供较为系统的信息资料。噪声对鱼类行为和鱼类听力、信息掩蔽、其他生理等多方面都会产生不利影响。噪声刺激会显著性增加鱼类游泳速度，减少觅食量，降低产卵成功率；导致鱼类的听力受损；阻碍鱼类之间信息交流，对鱼类寻求配偶产生不利影响，干扰鱼类回声定位；促使鱼体内生理激素、生理应激指标发生不适变化。强烈的噪声刺激会损伤鱼体的器官。目前的研究在实验声场场景、声波粒子运动、实验设置形式和试验周期监测等方面存在一定的不足，多数实验设计都无法模拟真实的声场场景；测量声音的质点运动分量方面鲜有研究；噪声暴露实验设置形式单一且很少进行周期性监测。针对当前的研究缺陷，建议从以下方面改进研究：（1）模拟真实声场场景；（2）探测声波粒子运动对鱼类的影响；（3）开展噪声暴露时间和播放形式方面的研究并进行周期性监测。     

Acoustic effects of underwater drilling and piling noise on growth and physiological response of Nile tilapia (Oreochromis niloticus)

Human‐generated noises are considered as underwater sound pollution with potential short‐ or long‐term impacts on behavioural responses and physiological reaction of aquatic living organisms. Few investigations are available so far on long‐term influences of impulsive and continuous sound sources on physiological response of fish. In the present study, opercula beat rates and pectoral wing rates were monitored as a physiological stress response of ventilation in Nile tilapia (Oreochromis niloticus) exposed to long‐term repeated and continued sounds generated from underwater construction work. Fish responded to underwater sound treatment with significantly increased opercula beat—and pectoral wing movements. Maximum ventilation rate was observed as a startle response of fish at initial exposure to underwater sound. The ventilation rates remained at high levels over the first 4 weeks and showed a declining trend thereafter. Fish growth was almost stable for the first 4 weeks, but shifted forward from day 45 onwards. We found strong evidence that fish could attune to repeated playbacks of underwater noise exposures since we found higher specific growth rates for the sound exposed fish from day 45 onwards until day 120, a so‐called ‘catch‐up growth endeavour’.     

An experimental study to evaluate predation threats on two native larval lampreys in the Columbia River Basin,USA

Experimental predation studies were conducted to evaluate and compare the predation threats of 10 species of native and non-native fishes on larvae of Pacific Lamprey, Entosphenus tridentatus, and Western Brook Lamprey, Lampetra richardsoni. The relative predatory threats were examined over four sets of binary factors, including the following: (a) short (2-day) or long (7-day) duration, (b) presence/absence of fine sediment, (c) live or dead larvae and (d) species of lampreys. Our short-term results showed a positive correlation with the sizes of predator fishes and consumed lamprey larvae. Also, most predator fishes had a significantly higher propensity to prey on lamprey larvae when sediment was absent. Conversely, this demonstrated the importance of sediment in protecting lamprey larvae from predation. Based on the predatory behaviour for live and dead larvae, predator fishes were classified into four groups using principal component analysis. Predation rates of larvae in sediment by piscivorous predators including Northern Pikeminnow Ptychocheilus oregonensis and Smallmouth Bass Micropterus dolomieu were lower and showed no differences even when the study duration was extended. In contrast, predation rates by benthic predators including White Sturgeon Acipenser transmontanus and Common Carp Cyprinus carpio, increased when we extended the study duration. This suggests that when given longer duration, benthic predators are more adept at consuming larvae within the sediment. These results provide important context for assessing the potential threat of predation on lampreys in streams, which is a key knowledge gap for lampreys.     

Effects of ambient acidity on chemosensory learning: an example of an environmental constraint on acquired predator recognition in wild juvenile Atlantic salmon (Salmo salar)

Abstract –  In many prey fish species, learning the identity of novel predators may be facilitated when novel predator cues and an aversive stimulus are presented together. Damage-released chemical alarm cues are typically released from the skin of prey individuals following mechanical damage and are known to mediate the learned recognition of novel predators. While such chemically mediated acquired predator recognition can provide increased survival benefits to prey, environmental constraints impeding learning may exist. For example, in several fish species the ability to detect chemical alarm cues is impaired in under acidic conditions and as such, inhibits this chemically mediated learning. In this experiment, we studied in two streams of different mean acidity level (pH c . 6.0 and 7.0), to assess if wild juvenile Atlantic salmon ( Salmo salar ) had the ability to acquire the recognition of a novel lemon essence odour when paired with conspecific chemical alarm cues. Our results demonstrate that under acidic conditions, no learned recognition of the novel odour occurred. In neutral conditions, however, salmon recognised the novel odour as a predation threat. This result suggests that ambient acidity creates an environmental constraint on chemically mediated learned recognition of a novel cue.