As a by standee over viewing the preparation and or the act of courtship in the coral reef fishes, one may think they have taken leave of their senses. The bicolor damselfish tends to quiver while performing a headstand. Blue pullers engage in a series of high-speed jumps. Lyretailfish swim in jerky zigzag patters. Frillfish goby undulates frantically against the sand. The Sergeant major rubs its body hard against the side of a rock or coral cavity and nips at these surfaces. (P 92)
These are methods by which coral reef fish readies a nest site or signals to prospective mates. Raped head-to-head circling and/or nose-to-belly nuzzling may signify that spawning is about to take place. Any of these performances are usually accompanied by dramatic changes in the patters or intensity of colors of the fish. Males and females tend to advertise their sex and availability through vibrant colors. This sexual dimorphism is most evident in such reef residents as groupers. The color patters change predictably from the “juvenile: to the “initial” subdued pattern of small adults to the “terminal” pattern in the largest adult males. The terminal male is the one with the brightest colors and gaudiest patterns.
The moon seems to play an important role in fish reproduction. According to Peter H. Pressley, it appears that the moon/s light may be as important as its gravitational pull. “Some fishes may use periods of maximum moonlight for effective nest guarding during the week or so it takes for many demersal eggs to incubate. Since the larvae of many dermersal-spawning species are light sensitive, bright moonlight may help to orient them towards the water’s shallows after nighttime hatching.” (P 96)
Regional weather patterns such as monsoons, periods of high wind velocity, and major current shifts affect procreation. “Extreme weather and fierce currents make it difficult for young fishes ready to assume reef niches to find their way out of pelagic waters.
“Some fishes migrate to spawn, some remain on the reef and spawn in pairs, some build reef nests where they guard their eggs, and a few actually protect their eggs, and a few actually protect their eggs in their mouths.” (P 97)
The Sergeant majors of the genus Abudefduf are usually found in tropical and subtropical shallows all over the world. In the inter months, they are generally solitary or swim in small groups. From April to August, many schools are formed among them and the migration begins. During its reproductive season, the early morning hours are spent feeding in the upper layers of plankton. At about 10:00 AM and 4:30 PM the eating in interrupted as the male of the species gather in groups of a few hundreds and move on to stake out their females.
Once the desired site and female are found, the leading males would separate form the crowd as it goes on and continues to “parade” for the right female. The Leading male of the species separate for the remaining of the pack and go on to spawn.
Pair spawners spawn in pairs formed after the male courtship display. This display consists of many males erecting all their fins and acting aggressively toward one another. These actions tend to impress the female of the species who then chooses a specific make and “the couple rush toward the surface in a spiral manner.” (P 100)
At least three species of Lionfishes, (the Pterois Volitans, Pterois radiata, and Dendrochirus brachypterus) form temporary pairs for spawning. “The males are usually possessive of their partners.” If need be, they engage in fierce defense for their “mate” privileges if another male approaches.
The third group of spawners are the nest builders. Some fishes build nests for the shelter of their eggs guarded usually by the male. However, in some species the female guards and in others, both parents guard their nest. The tiggerfishes use their undulatory swimming to excavate large nests in the sand. Here, the mass of eggs in laid, and are guarded by both parents. An interesting fact about this species is that after only one-day of tending the eggs, the female blows them gently into the ocean for further development.
The final group of spawners In the brooders. These fishes carry their eggs In their mouths. Brooding occurs among the cardinal fishes, (the family Apogonidae). The male has the job of incubation the eggs as well as carrying about the newly hatched eggs for up to two weeks.
Many species of fishes are hermaphrodites. Fishes are the only vertebrates that have hermaphrodite characteristics. There are two types of hermaphrodites. The simultaneous and the sequential hermaphrodites.
The simultaneous hermaphrodites have the mature sexual organs of both males and females and can reverse their sexual functions at will. The Caribbean harlequin bass ( Serranus tigrinus) is a simultaneous hermaphrodite with an interesting spawning methods. Many of the adult harlequin live together. At spawning peaks each member of a pair alternates in spawning as a male and a female. “The sequence begins when one fish, playing the female, displays its body in an ‘S’ shape with its exposed belly turned to the other fish. If so inclined, the invited partner approaches and the two proceed with a spawning rush. Often a role reversal takes place soon afterwards. With the opposite fish assuming the ‘S’ position.” (P 108)
Sequential hermaphrodites begin their lives as either a male or a female and may change into the opposite sex. In some species, all members begin their lives as females and later on, as needed, males are “created”. Some may begin as males and in time of need, turn into females.
Anemonefishes are protendrous (born as male) hermaphrodites. This fish spawns in pairs. An adult pair tolerates the juveniles being on their premise; however, another adult is not welcomed or accepted. If something should happen to the female, the partner takes on the role of the female and the largest of the juveniles becomes the breeding male.
Hermaphroditism makes the mating of any two mature fish, that happen to come together, possible.
The “evolutionary currency of success” is your fitness, or the number of offspring you leave behind. The larger the size of the fish, the higher its number of offspring and the higher its fitness. If a change in sex would increase the number of offspring, then there will be strong pressure to change sex as the fish grows older.
1) Desk Encyclopedia 1989 by Concord Reference Books, Inc.
2) http://www.audubon.org/campaign/lo/secrf.html Coral reef fish
3) http://www.fit.edu/Acadres/biology/tricas Coral reef fish
James Q. Wilson.