Triplefin Blenny Research Articles

Sneakers take a predation risk to gain sneaking opportunities

The act of mating increases predation risk by hindering an animal's ability to detect and escape from predators efficiently. Here, a novel issue of how alternative reproductive tactics differently influence these abilities was examined in the triplefin blenny, Enneapterygius etheostoma. A slow predator approach was presented to males with different mating tactics (territorial and sneaking) and mating states (mating and nonmating), totalling four combinations. Predator–male distance when males became wary was independent of tactics. The distance was shorter for mating males than nonmating males, but only when males faced away from the stimulus. Thus, mating state diminished the capacity for detecting danger similarly for both tactics. Predator–male distance when males initiated the escape was well predicted by mating state in sneakers, with shorter distances for mating individuals; however, the same was not obvious in territorial males. Consequently, sneakers escaped later than territorial males during mating, but both males escaped at a similar distance from the predator when in a nonmating state. Instead, mating territorial males returned to the spawning sites earlier than nonmating males. Overall, sneakers made bold escape decisions, whereas territorial males became risk prone when returning to the spawning sites. In conclusion, sneaking males pay a predation cost when mating.

Pause and travel: How sneakers approach closer to spawning sites under territorial vigilance

Male alternative reproductive tactics typically consist of territorial and sneaking tactics. In substrate-brooding fishes, sneakers try to steal fertilizations by suddenly rushing towards females from outside the spawning sites, but they are usually caught through territorial vigilance before rushing. Nevertheless, attention is seldom paid to how sneakers overcome territorial vigilance, which limits the ecological and evolutionary understanding of alternative reproductive tactics. I addressed this issue in the triplefin blenny, Enneapterygius etheostoma, by analysing sneaker behaviour recorded in the wild. Prior to rushing, sneakers gradually got closer to the spawning sites while repeatedly pausing and moving forwards but spent most of their time pausing. They moved slowly for short distances. Territorial males detected about three-quarters of the sneaking attempts. A sneaker was detected usually immediately after starting to move, indicating that movement was a major cause of sneaking failure. Longer and faster movements were detected more frequently, particularly further from spawning sites. Movements were also detected more when territorial males faced towards, rather than away from, the sneakers. This suggests that both sneaker performance and the attentive state of territorial males affect sneaking success. Sneakers more frequently started moving from behind territorial males than from in front of them, and were then less frequently detected. In sum, sneakers seemed to conceal their movements through pause-travel locomotion, adjusting their movements and choosing favourable situations. Nevertheless, they were still detected by motion-sensitive territorial males.

Optic-nerve-transmitted eyeshine, a new type of light emission from fish eyes

BackgroundMost animal eyes feature an opaque pigmented eyecup to assure that light can enter from one direction only. We challenge this dogma by describing a previously unknown form of eyeshine resulting from light that enters the eye through the top of the head and optic nerve, eventually emanating through the pupil as a narrow beam: the Optic-Nerve-Transmitted (ONT) eyeshine. We characterize ONT eyeshine in the triplefin blenny Tripterygion delaisi (Tripterygiidae) in comparison to three other teleost species, using behavioural and anatomical observations, spectrophotometry, histology, and magnetic resonance imaging. The study’s aim is to identify the factors that determine ONT eyeshine occurrence and intensity, and whether these are specifically adapted for that purpose.ResultsONT eyeshine intensity benefits from locally reduced head pigmentation, a thin skull, the gap between eyes and forebrain, the potential light-guiding properties of the optic nerve, and, most importantly, a short distance between the head surface and the optic nerves.ConclusionsThe generality of these factors and the lack of specifically adapted features implies that ONT eyeshine is widespread among small fish species. Nevertheless, its intensity varies considerably, depending on the specific combination and varying expression of common anatomical features. We discuss whether ONT eyeshine might affect visual performance, and speculate about possible functions such as predator detection, camouflage, and intraspecific communication.

Successful Operant Conditioning of Marine Fish in Their Natural Environment

The cognitive abilities of animals are challenging to assess. Typically, studies on visual discrimination in fishes are conducted in the laboratory neglecting the fact that acclimation of test subjects to the laboratory environment including artificial light conditions may affect the way in which fishes respond to visual stimuli. The aim of this study was to demonstrate that it is possible to train fishes on visual cues using food rewards, while free-roaming in their own territory under natural conditions. An acoustic secondary reinforcer was also included and its potential contribution to the training success was tested. We trained 27 specimens of the benthic triplefin blenny Tripterygion tripteronotum on either a black or white colored target. Training took on average ten days. In 15 binary choice trials, 23 fish discriminated successfully between rewarded target cue (CS ) and the unrewarded cue (CS−). Furthermore, we discuss the usefulness of acoustic secondary reinforcement in this study.

When to flee? The economics of sneakers facing territorial aggression

In species with alternative reproductive tactics, territorial males (guarders) are usually vigilant against sneakers, and aggressively attempt to eliminate them, imposing serious costs (injuries, sometimes death). Here I examined how sneakers escape from territorial attack in the triplefin blenny, Enneapterygius etheostoma, in the field, with the help of economic flight theory developed for predator–prey interactions. Sneakers hide around spawning sites for sneaking, but they are often detected and attacked by territorial males. Fleeing soon after the initiation of attack could reduce the risk of injuries. However, fleeing may be the wrong decision, resulting in a loss of benefit that could have been obtained by not fleeing, because of uncertainty about whether the sneaker is targeted. As the guarder–sneaker distance decreases, the target would become clear, and uncertainty is reduced accordingly. Therefore, it is predicted that flight initiation distance (FID, the predator–prey distance when escape begins) is determined by the cost–benefit balance. Two types of territorial aggression were identified: the ‘direct approach’, where the territorial male directly approaches a given sneaker, and the ‘reoriented approach’, where the territorial male turns to reorient and approaches it following an attack against the first target. A field study showed that sneakers fled earlier in the reoriented approach than in the direct approach. Model selection showed that FID in the reoriented approach was predicted by the guarder–sneaker distance at attack initiation (starting distance) alone, whereas FID in the direct approach was predicted by starting distance, the interaction between the approach speed of territorial males and the duration for which the sneakers monitored them. These results suggest that sneakers adjust flight decision rules to attack episodes, i.e. the economic decision in the direct approach, but the flush early decision in the reoriented approach. This study provides a novel example of adaptation in sneakers.

Three new species of triplefin blennies of the genus Enneanectes (Teleostei, Tripterygiidae) from the tropical eastern Pacific with a key to Pacific species of Enneanectes.

Three new species of the triplefin blenny genus Enneanectes found in the Pacific Ocean off southern Mexico are described. Two, Enneanectes glendae and Enneanectes macrops, are mainland species, while the third, Enneanectes exsul, is endemic to the Islas Revillagigedo. A key to the five species of Enneanectes known from the tropical eastern Pacific is provided.

First record of cleaning by a triplefin blenny in the Tropical Pacific

First record of cleaning by a triplefin blenny in the Tropical Pacific

Life history of the Hawaiian blackhead triplefin, Enneapterygius atriceps(Blennioidei, Tripterygiidae)

We described aspects of the life history of the small, cryptic, triplefin blenny, Enneapterygius atriceps, collected from the mouth of Kaneohe Bay, Oahu, Hawaii. We examined otolith microstructure to construct a von Bertalanffy growth curve, described a length–weight relationship, performed a detailed dietary analysis, used standard histological techniques to determine size at maturity and reproductive patterns, determined batch fecundity, and used an index of gonadal development to examine spawning seasonality. Enneapterygius atriceps is a remarkably short-lived species with low fecundity and a short, well-defined breeding season. Dietary analysis suggests this fish lives and feeds around the bases of dead coral heads. This study generated the first otolith-based growth curve for any member of the Tripterygiidae.

Fish-egg predation by the small clingfish Pherallodichthys meshimaensis(Gobiesocidae) on the shallow reefs of Kuchierabu-jima Island, southern Japan

We observed predation of demersal fish eggs by the clingfish Pherallodichthys meshimaensis on the shallow reefs of Kuchierabu-jima Island, southern Japan. The processes of egg predation varied with the target species. For targeting of eggs of the combtooth blenny Istiblennius edentulus, up to 65 individuals of the clingfish gathered around the I. edentulus nest hole. Some individuals succeeded in intruding into the hole and fed on eggs while the egg-guarding male of I. edentulus temporarily left the nest. For targeting of eggs of the triplefin blenny Helcogramma obtusirostris, solitary clingfish individuals closely approached spawning females of H. obtusirostris at nests on open surfaces of rocks. Most clingfish contained only fish eggs in their diets, and these fish-egg eaters had larger body sizes than individuals that mainly fed on harpacticoid crustacea. Thus, P. meshimaensis may change its feeding habits when growing to an obligate fish-egg eater targeting demersal egg spawners.

A Quantitative Assessment of the Reproductive System of the Mediterranean Cave‐Dwelling Triplefin BlennyTripterygion melanurus

Abstract.The breeding biology of the cave‐dwelling Mediterranean triplefin blennyTripterygion melanurus(Pisces, Blennioidei) was studied in the field. Two types of reproductive male were observed, territorial males and non‐territorial males. Territorial males establish territories for mating, but not necessarily for feeding, in caves and crevices at depths between 0.5 and 33 m. Territories can be settled in clusters in a single cave. Non‐territorial males occur in the vicinity of territories and attempt to parasitise matings of territorial males. Gravid females wait near territories where another female is spawning, rather than spawn with currently unmated territorial males. Waiting females intrude in matings and sometimes displace a spawning female. The frequency of mating of the territorial male, of sneaking and of female intrusions are higher in territories that border others than in isolated territories. Females may minimise predation risks both on themselves and on their eggs by spawning in clustered territories and by spawning with males that have more than one clutch of eggs. Territorial males must find a compromise between the benefits of attracting a female and the costs of parasitic spawning by sneaker males. The possibility that territorial males tolerate the proximity of other territorial males and accept a risk of cuckoldry is discussed. Parasitic spawning inT. melanurusis relatively rare and the gonadosomatic index in both non‐territorial and territorial males is low, indicating that sperm competition is probably not intense.

Male Parasitic Spawning in Two Species of Triplefin Blenny (Tripterigiidae): Contrasts in Demography, Behaviour and Gonadal Characteristics

Axoclinus nigricaudus and A. carminalis are blennioid fishes from the Gulf of California, Mexico. Males show alternative mating tactics; territorial individuals attract females while non-territorial individuals parasitically spawn with territorial males' females. Demography and gonadal characteristics were related to the degree of parasitic spawning (sperm competition) within and between species. Males of both species showed bimodal size distributions that largely reflected the two tactics. Territorial males spawned much more frequently than non-territorial males, but parasitic spawning was significant. Non-territorial males were more common and rates of parasitic spawning were much higher in A. nigricaudus indicating that it experienced higher sperm competition. In agreement with sperm competition theory, relative testis weight was greater in A. nigricaudus. In A. nigricaudus, the majority of parasitic matings were by non-territorial males, whereas in A. carminalis, both male-types parasitised frequently. Accordingly, only in A. nigricaudus did non-territorial males have relatively heavier testis than territorial males. In both species the testicular gland, that produces accessory products for sperm transfer, was large in territorial males, but small or undeveloped in non-territorial males suggesting male-types differ in fertilisation mode.