Egg concealment in ascidians by females of the Japanese tubesnout, Aulichthys japonicus (Gasterosteiformes), and its subsequent copulation

The reproductive behaviors of the Japanese tubesnout, Aulichthys japonicus, the only fish among gasterosteiform fish that conceals eggs in ascidians, were observed in aquaria. Yellow nuptial-colored males attending at ascidian courted gravid females. The nuptial color could be an advertisement to females for depositing sites, and courtships seemed to facilitate female spawning. The females spawned eggs above the ascidian and immediately placed their eggs with their mouths into the peribranchial cavity. Males never ejaculated on eggs after spawning, but attempted to copulate with females during a period of several minutes, and one or a few males with the remarkable nuptial color frequently copulated using their urogenital papilla. An evolutionary scenario of unique egg concealment and subsequent copulation is proposed.     

Female spawning migrations of the protogynous wrasse,Halichoeres marginatus

Spawning sites and spawning migration paths of tagged females of the protogynous wrasse,Halichoeres marginatus, were studied on the shallow reefs at Kuchierabu-jima Island, Japan. Males set up mating territories above prominent rocks on the offshore reef slope in the late afternoon, and pair-spawned with females, which had migrated there from their home ranges located in inshore areas. Small females migrated to the spawning sites near their home ranges, whereas large females migrated to various spawning sites located within a wide area, including downcurrent sites. Spawning at the downcurrent sites favors transport of eggs offshore, thereby increasing the female’s fitness. The spawning sites where an individual had spawned as a female were subsequently used for mating after it had changed sex. It is suggested that the wide migration of females to various spawning sites, enables the storing up of information on those sites, which later helps in the acquisition of mating territories after changing sex.     

Anti-egg predator behaviors of the small angelfish Centropyge ferrugatus (Pomacanthidae)

Synopsis Predation on eggs of the angelfish, Centropyge ferrugatus, was observed in the coral reefs of Sesoko Island, Okinawa, Japan. This angelfish released pelagic eggs in pairs at sunset after slow ascents. Of 99 matings of this angelfish, an omnivorous damselfish Amblyglyphidodon curacao approached in 25, and fed on the released eggs in eight cases. The spawning angelfish never attacked the egg-predators. Pairs of this angelfish avoided the egg-predators by delaying mating for several minutes during courtships, and by frequent changes of spawning sites. Of the 25 matings targeted by the egg-predators, the angelfish successfully avoided predation in 17 cases. Eight matings were failures mainly due to lack of any attempt to elude the predator, suggesting that the delayed matings on multiple spawning sites are effective anti-egg predator behaviors.     

Lek-like spawning,parental care and mating periodicity of the triggerfishPseudobalistes flavimarginatus (Balistidae)

Synopsis The triggerfishPseudobalistes flavimarginatus has a lek-like spawning system at Yonge Reef, Great Barrier Reef. Males migrate to a traditional mating ground where they establish territories enclosing nest sites and egg chambers. Females arrive several days later and choose a male for mating. There is biparental care of the fertilized eggs and a strict division of labour. Females appeared to be confined to the nest site by the male. Mating was semi-lunar: eggs were observed in nests several days before the new and full moons on days when high tide occurred near sunset. Differences were observed in the spawning system of another triggerfish (P. fuscus) between the Great Barrier Reef and the Red Sea. Observations of another triggerfish (Balistoides viridescens) are also reported.     

Predation of Northern Pike (Esox lucius L.) Eggs: A Possible Cause of Regionally Poor Recruitment in the Baltic Sea

Northern pike (Esox lucius) spawning habitat and egg mortality were studied in three spawning areas in 2001 along the Swedish coast of the Baltic proper: the Blekinge Archipelago, Kalmar Sound and coastal freshwater streams. Spawning peaked during the last week of April in streams, at temperatures ranging from 7.7 to 8.9 °C and during the first week of May in brackish waters, at temperatures ranging from 8.9 to 13.8 °C. Spawning occurred in shallow waters, at depths between 0.2–1.5 m, but generally most of the spawn was found in the shallowest areas. In streams, eggs were mainly attached to emersed vegetation, while in brackish sites pike eggs were well scattered among flooded emersed plants, submersed plants and filamentous algae. Mean egg density varied between 469–1829 m^–2 with the lowest density observed in Kalmar Sound. The calculated egg loss occurring from approximately one day after spawning to one day before hatching ranged from 41±7% in coastal streams to 67±6% in the Blekinge Archipelago and 100% in Kalmar Sound. The significant removal of eggs from spawning sites in Kalmar Sound and Blekinge was most likely due to predation from several fish species. In situ observations and stomach analyses suggested that many pike eggs in Kalmar Sound were lost to the three-spined stickleback (Gasterosteus aculeatus), a species that presently dominate the littoral small fish community. This study therefore suggests that egg predation by sticklebacks and other fishes may be a possible cause of the reported poor recruitment of coastal pike populations in the Kalmar Sound region.     

Spawning timing of the cleaner wrasse, Labroides dimidiatus, on a warm temperate rocky shore

We observed spawning behaviors of the haremic cleaner wrasse Labroides dimidiatus at a rocky reef in southern Japan. Females released pelagic eggs daily from June to September after a spawning ascent by pairs. When the high tide occurred between noon and evening (quarter moon to new or full moon), they spawned around the time of the tide providing fast offshore currents. For the rest of the lunar cycle, spawnings occurred during late afternoon independent of the state of the tide at the time of day. This spawning pattern is quite different from that of conspecifics on coral reefs that always spawn around the high tide at all lunar stages to avoid potential egg predators. The wrasse ascended high in the water column, probably because of its predator-immune characters as a cleaner. The steep slope of the study site seemed to contribute to releasing gametes far above aggregating planktivores. Thus, gametes were not subject to heavy predation. Current direction might not always affect survival of spawned pelagic eggs on the temperate reefs so crucially as it does on coral reefs. We conclude that spawning during unfavorable tidal conditions during the daytime may be better than spawning during the best tidal condition in the crepuscular period when predation pressure on adults will be high. Intraspecific variation in the timing and location of spawning of the wrasse may result from different conditions for larval survival. Received: February 6, 2000 / Revised: June 16, 2000 / Accepted: July 17, 2000     

Reproductive behavior and mate fidelity in the monogamous goby,Valenciennea longipinnis

Reproductive behavior and mate fidelity of the gobiid fish,Valenciennea longipinnis, were studied on the coral reef at Sesoko Island, Okinawa, Japan. These fish usually live in pairs, not only foraging together for benthic animals in sandy areas, but also constructing several burrows within their home range. Before spawning, both fish, although mainly the male, constructed a mound, piling up dead-coral fragments, pebbles, shells, sand and algae onto one of the burrows. After spawning an egg mass on the ceiling of the burrow, the female stayed outside and continued the construction and maintenance of the mound for 3–5 days until hatching, while the male tended the eggs inside. Mate guarding of females seemed to prevent males from monopolizing several females. Although some pairs showed mate fidelity through several spawnings, more than half of the pairs broke up after only one spawning. The pair bond was broken by mate desertion and the disappearance of each sex. Both sexes preferred larger spawning partners; larger females spawned more eggs and larger males provided better egg care. Mate desertion occurred when larger potential mates, relative to the current partner, became available. The frequency of solitary individuals was higher in males than in females, resulting in females deserting their mates more often than males. Two factors seem to have facilitated mate desertion: (1) occurrence of size mis-matched pairing and (2) overlapping home ranges.     

Communal Spawning in the Common Frog Rana temporaria– Egg Temperature and Predation Consequences

Females of the common frog, Rana temporaria, spawn synchronously at communal breeding sites, forming a communal egg mass of individual spawn clumps. A total of four spawning sites were studied. In the centre of the communal egg mass, daily maximum temperature was higher and minimum temperature lower than further out. Spawn clumps in the centre of the communal egg mass developed faster than single spawn clumps. In the centre of the egg masses, some spawn clumps suffered almost total egg mortality. This was probably the consequence of a cold spell with sub‐zero temperatures in combination with a tendency for low minimum temperatures in the centre. In a laboratory study, worm leeches, Erpobdella spp., fed readily on eggs of common frog, while horse leeches, Haemopis sanguisuga, hardly ate any eggs. At the spawning sites, most worm leeches were found in single spawn clumps, far from the communal egg mass. Females which spawned late, when most of the spawning was over, preferred to spawn in the centre of the communal egg mass. This suggests that there is a net advantage for eggs in spawn clumps laid in the centre.     

Aspects of the spawning of western Atlantic butterflyfishes (Pisces: Chaetodontidae)

Synopsis The status of knowledge of spawning among the five shallow waterChaetodon species in the western Atlantic is reviewed. Spawning has been observed for three species in Puerto Rico, St. Croix and the Bahamas, with possible courtship in a fourth.Chaetodon aculeatus spawned near the time of sunset over objects on the reef as single female/male pairs or as two females and one male, with pair spawning in rapid succession. Spawning occurred during much of the lunar month from February to April and it is uncertain whether any lunar periodicity to spawning exists. Male-male aggression was noted. Spawning sites (coral heads) were alternated daily and it is likely that females spawn only once every two days. A single female produced as many as 2090 eggs in a single spawning.Chaetodon capistratus spawned during much of the lunar month from February to April. It spawned about 5 min afterC. aculeatus, occasionally using the same sites, and alternated sites daily. A female produced as many as 3710 eggs in one spawning.Chaetodon striatus spawned from February to April but it is unknown if it has any lunar spawning cycle. No predation attempts by piscivores on spawning adults were seen. Predation byMelichthys niger on eggs ofC. striatus occurred. No egg predation was observed forC. aculeatus andC. capistratus. With an assumed four month reproductive season, alternate day spawning and observed egg production values,C. aculeatus andC. capistratus produce respectively about 100 000 and 200 000 eggs per large female per year. The reproductive strategy of smaller species may be to produce moderate numbers of eggs per day over a spawning season of at least a few months while larger species may produce more eggs per day for a shorter period.     

The beach‐spawning California grunion Leuresthes tenuis eats and digests conspecific eggs

Apparent egg cannibalism was investigated in the beach‐spawning California grunion Leuresthes tenuis. Three hypotheses were tested to determine whether L. tenuis regularly consumes and efficiently digests conspecific eggs. First, examination of the gut contents of adults collected at four spawning sites over two seasons showed that the intestines of most fish from all the sites (57–87%, n ≥ 30, each site) contained L. tenuis eggs. The two other hypotheses focused on digestion of the eggs. First, the force required to crush cannibalized eggs was significantly less than that for uncannibalized eggs (fertilized or unfertilized), indicating that ingestion weakens the egg chorions. Second, conspecific eggs fed to fish held in the laboratory visibly degraded as they passed through the gut. The eggs lost c. half of their protein content and about two‐thirds of their lipid content as they passed from proximal to distal regions of the gut, indicating that digestion occurred. Digestive enzyme activities of the gut further confirmed that L. tenuis can break down the contents of ingested eggs. Trypsin activity decreased and aminopeptidase activity increased posteriorly along the gut, whereas amylase and lipase activities exhibited less clear patterns by gut region. As far as is known, this study is the first to show that L. tenuis is an egg cannibal.     

Spawning site of the fluvial eight-barbel loach, Lefua sp., in the natural environment

The spawning site of the fluvial eight-barbel loach, Lefua sp. (sensu Hosoya, 1993; Japanese name: nagare-hotoke-dojo), an endangered species, was investigated by searching for fertilized eggs in June and July 1995–1997 in an upper reach of the Kako River, Hyogo Prefecture, Japan. We obtained one egg each by a random sampling with agitating the river bottom (80 trials) and by collecting drift samples (89 trials). This finding indicates that the eggs were not scattered on the bottom or into the water column after being spawned. Two individual males were observed to patrol around particular interstices occurring under the buried cobbles and under the boulders that formed the riverbank. Males pecked other individuals that approached around the interstices. We obtained 9 and 15 eggs, respectively, from two such interstices in only two collection trials. The interstices were suggested to function as the spawning sites of this endangered fish in nature.     

Predominant maternal egg care and promiscuous mating system in the Japanese filefish,Rudarius ercodes (Monacanthidae)

Synopsis Reproductive behavior of the Japanese filefish, Rudarius ercodes, was studied at the rocky reef off Koinoura, northern Kyushu, Japan, between June and October 1989. Aggressive display was observed between males, but they were not territorial. Males had four types of courtship behavior: vibrating, tail bending, leaning and nuzzle. Spawning occurred early in the morning. A female and 1–3 male(s) mated together on brown algae. Each female spawned repeatedly with an interval of 6–12 days. Females cared for eggs and embryos from just after spawning until hatching, 2–4 days. Female egg care consisted of tending and guarding. Females tended eggs by blowing water on them and by fanning them with their pectoral fins. Females guarded eggs by driving away fish passing nearby. In some cases, males also guarded eggs by staying near the eggs and driving away conspecific males. Whether a male cares for eggs with a female seems to be affected by the form of mating (pair mating or single female-multiple male mating), and the probability of further reproduction after spawning. Dominant males showed a tendency to pair with a specific female intermittently over a two-month period. Mating, however, did not always occur between members of such pairs, and mates appeared to be inter-changeable with a promiscuous mating system.     

Fish-egg predation by the small clingfish <Emphasis Type="Italic">Pherallodichthys meshimaensis</Emphasis>(Gobiesocidae) on the shallow reefs of Kuchierabu-jima Island,southern Japan

Synopsis 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.     

Spawning behavior of the pygmy leatherjacket Brachaluteres jacksonianus (Monacanthidae) in southeastern Australia

Spawning behavior of the pygmy leatherjacket Brachaluteres jacksonianus was studied in southeastern Australia. Prespawning females thrust the snout repeatedly into spawning substrata, while males exhibited courtship display and nuzzled the female’s face. The females and males touched their abdomens in pairs and released gametes. No parental egg care was observed after spawning. Fertilized eggs measured 0.74 mm in diameter, and each clutch contained 50–191 eggs. The eggs were attached to filamentous red algae, which were found on the surface of the seagrass and other substrata. Reproductive ecology of B. jacksonianus is similar to that of congeneric Brachaluteres ulvarum, although selection of spawning substrata differed in two species.Supplementary material to this paper is available in electronic format at http://dx.doi.org/10.1007/s10228-005-0272-8     

Behavioral changes of a Brazilian endemic damselfish Stegastes rocasensis when guarding egg clutches

This study aimed at comparing the feeding, territorial and agonistic behavior of the Rocas Gregory Stegastes rocasensis when guarding egg clutches. This was accomplished through underwater observations of 80 S. rocasensis individuals observed in four sampling sites in the Fernando de Noronha archipelago (SW Atlantic). Several differences were detected in the behavior of S. rocasensis, such as the reduced size of the territory, the feeding preferences and the aggressiveness towards intruders. Males guarding eggs defended territories twice as small as the ones that did not present egg clutches inside their territories. Additionally, they fed mostly on turf algae, while individuals without eggs in their territories fed mostly on turf and macroalgae. Fish guarding egg clutches elicited agonistic reactions mainly towards planktivores and omnivorous fishes, which could potentially prey on their eggs, while individuals without eggs clutches in their territories elicited agonistic reactions mainly towards herbivorous fishes. The results of the present study reinforces that damselfishes are able to identify the intruder’s identity and elicit agonistic reactions only toward species that may represent a threat to their eggs and/or farmed algae.     

Semilunar spawning cycle of the humbug damselfish Dascyllus aruanus

A very distinct semilunar spawning cycle was found in a population of the damselfish Dascyllus aruanus on the coral reefs of Sesoko Island, Okinawa. Spawning occurred from June to September, only in the early morning, during a period of 2–4 days immediately before or around the time of the new and full moon. Males cared for the eggs deposited on the substrate for 2.5 days until hatching. Hatching occurred just after sunset, i.e., at the high tide of spring tide; the strong ebb current then would rapidly disperse the newly hatched larvae offshore. Females tended to synchronize spawning in a male's nest, also because multiple clutches in a nest would be more likely to survive until hatching. Thus, the distinct semilunar spawning cycle may favor females in reducing mortality of both eggs and larvae. Received: July 9, 1999 / Accepted: January 29, 2000     

Mate choice and cannibalism in a natural population of a stream goby,Rhinogobius sp.

Breeding ecology of the stream goby,Rhinogobius sp. LD (Large Dark), was investigated under natural conditions. Males selectively courted females of similar size to lead them to the nests, whereas females followed courting males preferentially when the relative male size was greater. Male-male competition for a female was relatively infrequent and not severe. Developmental stages of eggs and egg numbers in one nest indicated that males receive 1–3 clutches during one breeding cycle. Males guarding multiple clutches frequently ate some of the eggs, but those guarding single clutches rarely did so. Gravid females in the nest also frequently cannibalized eggs laid by a previous female, probably in order to extend the area available for egg deposition. Mate choice in this species is discussed in relation to paternal ability, limitation of available spawning area and the female-biased sex ratio.     

Aspects of the spawning of labrid and scarid fishes (Pisces: Labroidei) at Enewetak Atoll,Marshall Islands with notes on other families

Synopsis Spawning of 32 species of Labridae and 13 species of Scaridae was seen at Enewetak Atoll, Marshall Islands. Most spawned on a reef bisecting the main ocean-lagoon passage which had strong tidal currents. Others spawned on lagoon reefs and in Halimeda beds. Polygynous haremic, lek-like and promiscuous mating systems were found which were species specific. Data on reproductive patterns, sexual dichromatism, sexual dimorphism, seasonality and spawning behavior were determined. Many spawned during the day in a time-phase dependent pattern from near sunrise to sunset. Scarid spawning began at slack high water or after when currents were starting to move out of the lagoon. Labrid spawning usually started about 30 min later with some continuing up to 2 h after high tide. With high tide before sunrise, scarid spawning began 30–50 min after sunrise as the current started flowing over the reef. With high tide near sunset, spawning occurred with an incoming current. Most labroids spawned on all phases of the moon. Acanthuridae (6 spp), Caesionidae (1 sp.) and Zanclidae (1 sp.) spawned after high tide at the same time as labroids. Pomacanthidae (5 spp.) spawned only shortly before sunset without reference to tidal currents. Fishes producing pelagic eggs at the lagoon-ocean channel spawned (1) at or slightly after high tide (44spp.), (2) in late afternoon without reference to tide (6 spp.) or (3) after slack low water (1 sp. ). Spawning style can vary within a single species in different environments. Despite the presence of many piscivores, no successful predation on spawning adults was seen. Predation on newly released eggs was uncommon. Labrichthys unilineata and Anampses twistii attempted to defend their eggs for a few sec after release. Attacks by piscivores on spawning adults on tropical reefs occur once per 100–1000 spawnings. Most are wary when preparing to spawn and prespawning behavior is easily interrupted. The risk from piscivores goes down and spawning ascent speed decreases with increasing size of spawners. Egg predation by zooplanktivores is less for pair spawners than group spawners possibly due to less conspicuous gamete clouds and times of spawning. Increasing height of egg release, speed and length of the spawning ascent, and trajectory alteration of ascending adults are believed to make it more difficult for zooplanktivores to locate eggs after release. For labrids, permanent full sexual dichromatism was found among haremic, lek-like and promiscuous mating systems. Species with temporary full dichromatism, permanent and temporary partial dichromatism and monochromatism were haremic. Smaller scarids were believed to have lek-like, and larger species haremic, mating systems. Smaller scarids had male looping behavior and post spawning displays, plus faster spawning ascents and different locations for egg release than larger ones. Eggs of 21 labrids were spherical or nearly spherical, ranging from 0.55–0.80 mm in diameter, and most had one oil globule. Among 7 is scarids, 6 had spindle-shaped eggs ranging from 1.25 ×0.50 mm 2.14× 0.48 mm while one had a nearly spherical egg. One scarid egg lacked an oil globule.     

Expulsion of miniature radio transmitters along with eggs of muskellunge and northern pike––a new method for locating critical spawning habitat

Identification and protection of critical spawning habitat for muskellunge Esox masquinongy and northern pike Esox lucius is important for preserving the reproductive potential of both species. In this study, we implanted miniature radio transmitters through the oviduct into the egg masses of female muskellunge and northern pike just prior to spawning. This non-surgical procedure was a novel approach for identifying spawning sites when transmitters were expelled with the eggs during egg deposition. Preliminary studies in three lakes showed that muskellunge and northern pike deposited many of the transmitters in likely spawning habitat. An inability to find eggs limited our validation of this method, but nevertheless, a relatively high proportion (70%) of northern pike larger than 690 mm (27.2 inches) expelled transmitters in a previously known spawning area in Willow Lake, Minnesota. Shoreline vegetation in that area consisted primarily of sedges Carex spp., and the adjacent water was shallow with substrate consisting of large mats of water bulrush Scirpus subterminalis. A lower proportion (50%) of muskellunge expelled transmitters in Elk Lake, Minnesota. Water depth at likely spawning sites averaged 1.1 m (3.6 feet) and vegetative cover was variable, but Chara spp. was common to most sites. In Moose Lake, Minnesota, containing sympatric populations of muskellunge and northern pike, 60% of muskellunge and 90% of pike expelled transmitters. Chara spp. beds were the predominant substrate where transmitters were expelled in Moose Lake, but the two species deposited transmitters on deepwater bars (3.7–5.2 m) in addition to shallow near-shore habitat. These results suggest more flexibility in depths used for spawning than typically reported for muskellunge and northern pike.     

Salvelinus namaycush spawning substratum attracts egg predators and opportunists through chemosensory cues

Two separate field experiments were conducted in a series of small boreal lakes to test for the attraction of egg predators to lake trout Salvelinus namaycush spawning shoals and subsequently to determine whether chemosensory cues attract egg predators to these sites. In the first experiment, minnow traps set on spawning sites captured significantly more egg predators than those set on structurally similar non‐spawning sites. Captures of slimy sculpin Cottus cognatus, common shiner Luxilus cornutus, blacknose shiner Notropis heterolepis and virile crayfish Orconectes virilis were more than double on spawning sites relative to non‐spawning sites for the two study lakes. To test whether chemosensory cues could attract egg predators to S. namaycush spawning sites, paired minnow traps were placed on eight to 10 sites in each of the three study lakes; one trap contained visually concealed S. namaycush spawning substratum and the other with visually concealed non‐spawning substratum. Traps containing spawning substratum consistently captured more fish and had higher mean daily catches than those that contained non‐spawning substratum. The combined results demonstrate a greater prevalence of egg predators on S. namaycush spawning shoals that appears to be the result of chemosensory attraction to spawning substratum.