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Male Terriotriality

Triggerfish males migrate to their traditional spawning site prior to mating and establish territories. Some male species (i.e. Balistes carolinensis and Pseudobalistes flavimarginatus) build hollow nests on within their territories. Triggerfish males are fierce in guarding their territories as territory is essential for reproduction. Male territory is used for spawning and parental care, and most of male territories are located over a sandy sea bottom or on a rocky reef. A single male territory usually includes more than one female, and the male mates with all the females residing in or visiting his territory (polygyny). In Hachijojima, Izu Islands, Japan, one male crosshatch triggerfish (Xanthichthys mento) has up to three females in his territory at the same time, and mates with them in pairs. Each male red-toothed triggerfish (Odonus niger) mates with more than ten females in his territory on the same day. Yellow margin triggerfish (Pseudobalistes flavimarginatus) also exhibits polygyny mating.

Spawning and Biparental Care

Triggerfish's spawning is timed in relation to lunar cycles, tides, and time of changeover of tides. In relation to lunar cycles, eggs are observed 2-6 days before the full moon and 3-5 days before the new moon. In relation to tides, spawning happens 1-5 days before the spring tide. Finally, in relation to timing of tides, eggs are observed on days when high tides take place around sunset.

Male and female triggerfish perform certain pre-spawning behaviors: blowing and touching. Male and female blow water on the sandy bottom (usually in the same spot at the same time) and sets their egg site. They touch their abdomens on the bottom as if they are spawning. During actual spawning, eggs are laid on the sandy sea bottom (triggerfish are demersal spawners despite their large size). Eggs are scattered and attached to sand particles. Triggerfish eggs are usually very small (diameter of 0.5-0.6mm), and easily spread by waves. After spawning, both male and female participate in caring for the fertilized eggs-biparental egg care. Female triggerfish stays near the spawning ground-around 5 meters off the bottom-and guards the eggs within her territory against intruders. Some common intruders include Parupeneus multifasciatus, Zanclus cornutus, Prionurus scalprum and conspecifics. Besides guarding, females roll, fan and blow water on eggs to provide oxygen to the embryo, thereby inducing hatching. This behavior of female triggerfish is called 'tending,' and males rarely perform this behavior. Male triggerfish stays at farther above from the eggs and guard all the females and eggs in his territory. Males exhibit aggressive behaviors against conspecific males near the boundaries of their territories.

Mating Systems

In crosshatch triggerfish (Xanthichthys mento) and yellow margin triggerfish (Pseudobalistes flavimarginatus), eggs are spawned in the morning, and they hatch after the sunset on the same day. After hatching of embryos, the female crosshatch triggerfish leaves the male territory. This mating system is an example of male-territory-visiting polygamy. Triggerfishes exhibit other types of mating system as well, such as a non-territorial-female (NTF) polygyny and territorial-female (TF) polygyny. In NTF polygyny, non-territorial females stay in the male's territory and reproduces. In TF polygyny, females own territory within a male's territory and spawns in her territory.

Burrow Building

Gobies usually live in male-female pairs that construct and share burrows. The burrows are used as a shelter and a spawning place. Gobies use mouth to dig into the sea bottom, removing dead coral-fragments, rubbles, and benthic algae to build burrows. Gobies maintain their burrows by fanning away sand inside the burrow. Furthermore, coral rubbles are used to block the entrances of burrows. One goby can carry as many as nine pieces of coral rubbles per minute. Gobies also build a mound of 6-13 cm high over one of the entrances of their spawning burrow. The mound let the water flow fast over the mound, creating a low-pressure spot. The water flow created by the mound helps providing oxygen for the eggs, similar to the effect of the fanning done by the male goby. An interesting fact about the mound is that during parental care, when females are removed, the mounds loose their heights. Then, males give upon the eggs and eat them, preparing for the future mating opportunity. The burrows vary in size depending on the size of the goby species. In some species of average size 15 cm, the burrows are 30 cm high with 25-60 cm diameters. While the burrow building is a cooperative behavior done by the male and female gobies, males usually put more effort in the burrow maintenance than females. Female gobies feed more instead. This could be because the reproductive success is optimal when females put more energy in preparing for the reproduction.

Kleptogamy

Kleptogamy refers to the sneaking behavior during reproduction. Female gobies prefer male gobies with large bodies. Since not many males have large bodies, some small males decide to cheat instead of putting energy in finding mates and fulfilling the responsibility as males (i.e., protecting the territory and the female). The sneakers wait in the vicinity of the spawning ground of paired gobies. The sneakers then release their sperms on the spawning ground as soon as the paired females release their eggs. Even though sneakers’ sperms fertilize some eggs, the paired males cannot distinguish the eggs fertilized by the sneakers from those fertilized by their sperms. The paired males equally give parental care to all the eggs. Therefore, the sneakers can save energy, and they can put more effort into finding new targets for cheating. The sneakers are also referred to as pseudo-females, since they are small and hardly distinguishable from females. The paired males are sometimes called “bourgeois” males. The cost of kleptogamy is that the sneakers can receive aggressive attacks from the paired males (or bourgeois males) that are usually large and strong. For small sneakers, the attacks by the paired males can be detrimental and often lead to death.

Sex Change

A few species of goby, such as blackeye goby and bluebanded goby, can change their sexes. Sex change is possible in these gobies, since the external genitalia for males and females do not differ much. The external genitalia of gobies are not very elaborate either, so transforming is relatively easy. Sex changes can take from days to weeks. Most sex changes in gobies are female-to-male changes, though male-to-female changes are observed as well. Female-to-male changes are not only seen in gobies but also in wrasses, damselfishes, and sea basses. Female-to-male changes occur usually when the resident male is dead. The dominant female turns into the male and fills up for the dead male, allowing mating to happen. Male-to-female changes occur when the females have preference for specific features in males. For example, female gobies prefer large males, and a few large males mate with multiple females, whereas small males loose their chance to mate. Small males either choose to become sneakers (kleptogamy) or to transform into females because all females technically have high mating rates. By turning into females, males can ensure that they produce many descendants. Some gobies have extraordinarily developed sex-changing ability. Gobiodon historio from the Great barrier Reef exhibits bi-directional sex changes. Gobiodon historio is one of the very few species that can change sexes in both ways. In an experiment with Gobiodon historio, when two females that turned into males were positioned on the same reef, one of them transformed back into a male goby.

Sex Determination

Sex determination in coral goby Gobiodon erythrospilus does not occur until juvenile gobies meet potential mates. Confronting a potential mate can be difficult for Gobiodon erythrospilus juveniles, since most coral resources, crucial for attracting mates, are occupied by pre-existing paired gobies. Juveniles can only meet potential mates when one member of the pre-existing pairs dies. Juveniles’ sexes are determined according to the sexes of their potential mates. When a juvenile goby meets a female, it becomes a male, and it turns into a female when the partner is a male. This type of sex determination is referred to as “socially-influenced” sex determination.

Use of Landmarks

Some gobies remember landmarks within short distance and use the information to get away from predators. Small frillfin gobies Bathygobius soporator live in intertidal zones and are confined to tidal pools at low tides. When they feel any potential danger, they jump from pool to pool and with great accuracy. These gobies explore the pools during high tides when they can swim through all of them, and memorize how each pool connects the others. In a new environment, gobies do not show jumping behaviors or jump into wrong pools. Nevertheless, after one night, during which they explore the new pools and memorize the paths, gobies can exhibit the same accurate jumping behaviors.

Research

A study was done to understand how gobies react to changing habitat. Gobies were given two choices: a safe habitat with less food and a dangerous habitat with more food. Results from both the satiated and hungry gobies revealed that gobies, when confronted with the trade-off between foraging and avoiding predation, made choices that would better their foraging. Several studies were done to learn more about gobies’ reproduction behavior under specific conditions. In one study, the correlation between predation threat and the duration of courtship before mating was drawn. It showed that gobies shortened their courtship behavior when the predator was around. Another study on gobies’ physiological changes during spawning season indicated that gobies, due to day and night spawning, suffered from lack of sleep throughout the entire spawning season.

REDLIP BLENNIES

Reproduction

Reproduction in the redlip blenny happens year-round during ten days before and four days after the full moon in each month. The male and female pair spawns in the first three hours of daylight, and the female moves to the male territory. The male has to prepare a nest for depositing eggs. In order to prepare a nest, the male makes a "small box-like" space in its territory and removes coral rubbles and dead algae crusts from the space. One male redlip blenny usually has five nests, and depending on the popularity of each nest, the male would move from one nest to another. Usually the nest favored by females has a larger inner surface area and volume than the less favored nest. When a female redlip blenny enters a male's nest, the female chooses whether or not to mate. Larger males with larger nests exhibit better chance of mating success than smaller males. During spawning season, males reduce their feeding. The eggs are deposited in a single layer, and the male guards and blows air to the eggs (paternal care) until they hatch as planktonic larvae. The eggs in one nest may be at different developmental stages because the male redlip blenny mates with multiple females (polygyny).

Mate Choice

Female mate choice, in general, primarily relies on either the gene quality of the male or the non-genetic quality such as parental care which can still increase the survival rate of the offspring. Female redlip blennies choose males based on their sizes. At a basic level, this is because the size of the male is a good indicator of quality genes, as size is highly correlated with survival. At a more species-specific level, the size of the male redlip blenny shows the male's ability to protect the eggs from microbial infection. Female redlip blennies also take males' allopaternal care into account when choosing mates, since allopaternal care proves the male's ability to protect the eggs from predators. Furthermore, a statistical study showed that female redlip blennies may prefer older males because age reflects survival ability.

Parental Care

Most parental care in fish takes the form of paternal care, which means that the male primarily gives care to the eggs. The parental care in redlip blennies is also performed by the male. A male redlip blenny exhibits representative paternal care behaviors such as protecting and blowing oxygen to the eggs. Besides, the male also performs a non-typical paternal care: rubbing its anal-urogenital region over the nest internal surface during spawning. The male redlip blenny has a sex specific organ at the anal-urogenital region that produces antimicrobial substances. Therefore, by rubbing the anal-urogenital region over the nest internal surface, the male protects its eggs from microbial infections, one of the most common causes for the lethality in baby fishes. Larger males have larger organs at their anal-urogenital regions and thus can produce better protection for the eggs than smaller males. Consequently, female redlip blennies choose their mates based on their sizes. Another atypical paternal care in redlip blennies is that the male indiscriminately cares for its own eggs and foreign eggs. When a male takes over the deserted nest, he will guard and care for the existing eggs in the nest (i.e. allopaternal care). While it seems to be a huge disadvantage at an evolutionary level, allopaternal care actually attracts more mates because safe eggs prove the male's capacity to protect the eggs against predators. The allopaternal behavior also shows the female that the male is a trustable mate who will remain after mating and provide the eggs with a good amount of parental investment.

Territoriality

Territorial behavior is usually performed to defend resources such as food, shelter, possible mates, spawning sites, or offspring. Redlip blennies live among rocks and coral reefs, and they are benthic. A redlip blenny generally exhibits aggressive territorial behaviors towards other benthic fishes, as they may take over its shelter and spawning site. Its territorial behavior is most extreme towards conspecifics. This is because the conspecifics share exactly the same set of resources, and thus the competition is the highest. A redlip blenny shows hostile reactions of varying degree not only to intruding conspecifics but also to barely transgressing conspecifics. Due to this severe territoriality, the redlip blennies that have lost their territories experience a great difficulty in finding new territories. Empty territories are often shared by neighboring fish without much competition. Despite severe territoriality, during the periods of lower adult blenny density, many blennies recruit to the new possible residential area to compete for territories. After recruitment, each dwelling blenny only owns half of its pre-recruitment territory.

Swimming in Larvae

Many fishes have a swimbladder that provides buoyancy. However, redlip blennies never own a swimbladder throughout their entire lives. The lack of a swimbladder does not affect adult redlip blennies, since the adult blennies have dense bodies and have adjusted to the benthic life. In fact, lacking swimbladder helps the metabolism of metamorphosis in the adult blennies. However, the larvae need a way to float for survival. In the redlip blenny larvae, buoyancy is provided by a significant storage of lipids in the larval liver.