Damselfish

Damselfishes are those within the subfamilies Abudefdufinae, Chrominae, Lepidozyginae, Pomacentrinae, and Stegastenae within the family Pomacentridae.[1][2] Most species within this group are relatively small, with the larges species being about 30cm (12 in) in length.[3] Most damselfish species exist only in marine environments, but a few inhabit brackish or fresh water.[3] These fish are found globally in tropical, subtropical, and temperate waters.[4]

Neon damselfish from East Timor
Cocoa damselfish (Stegastes variabilis)

Habitat

Many species live in tropical rocky or coral reefs, and many of those are kept as marine aquarium pets. Their diets include small crustaceans, plankton, and algae. However, a few live in fresh and brackish waters, such as the freshwater damselfish, or in warm subtropical climates, such as the large orange Garibaldi, which inhabits the coast of southern California and the Pacific Mexican coast.

Foraging
Canary damsel

The domino damselfish D. albisella spends the majority (greater than 85%) of its daytime hours foraging. Larger individuals typically forage higher in a water column than do smaller ones. Damselfish of all sizes feed primarily on caridea and copepods. Males have relatively smaller stomach sizes during spawning season compared to females due to the allocation of resources for courtship and the guarding of nests. When current speeds are low, the damselfish forages higher in a water column where the flux of plankton is greater and they have a larger food source. As current speeds increase, it forages closer to the bottom of the column. Feeding rates tend to be higher when currents are faster. Smaller fishes forage closer to their substrates than do larger ones, possibly in response to predation pressures.[5]

Territoriality

There are many examples of resource partitioning and habitat selection that are driven by aggressive and territorial behaviors in this group. For example, the threespot damselfish S. planifrons is very defensive of its territory and is a classic example of extreme territoriality within the group.[6] One species, the dusky damselfish S. adustus spends the majority of its life within its territory.[7]

Domestication of Mysid Shrimps

Longfin damselfish (Stegastes diencaeus) around Carrie Bow Cay, Belize (16°48.15′N, 88°04.95′W) is shown to actively protect planktonic mysids (Mysidium integrum) in their reef farms. The mysids fertilize the algae grown in the reef farms with their excretes which in turn helps the damselfish who feed on algae to be healthier.[8] In the reef farms that house mysids, damselfish aggressively defends the farm area against other fish that would predate on the mysids, significantly more so than they do when their farms do not house mysid shrimps. These damselfish would eat similar small invertebrates. Despite of that, they are docile towards mysid shrimp. In the area, mysid shrimps are not found in swarms except in the farms maintained by damselfish. All these observations point to a pet-like relationship between the mysid shrimps and longfin damselfish in the area, with damselfish being the domesticator and mysids being the domesticate.

Courtship

In the species S. partitus, females do not choose to mate with males based on size. Even though large male size can be advantageous in defending nests and eggs against conspecifics among many animals, nest intrusions are not observed in this damselfish species. Females also do not choose their mates based upon the brood sizes of the males. In spite of the increased male parental care, brood size does not affect egg survival, as eggs are typically taken during the night when the males are not defending their nests. Rather, female choice of mates is dependent on male courtship rate. Males signal their parental quality by the vigor of their courtship displays, and females mate preferentially with vigorously courting males.[9][10]

Male damselfish perform a courtship behavior called the signal jump, in which they rise in a water column and then rapidly swim back downward. The signal jump involves large amounts of rapid swimming, and females choose mates based on the vigor with which males do so. Females determine the male courtship rates using sounds that are produced during signal jumps. As the male damselfish swims down the water column, it creates a pulsed sound. Male courtship varies in the number and rates of those pulses.[11]

In the beaugregory damselfish S. leucostictus males spend more time courting females that are larger in size. Female size is significantly correlated with ovary weight, and males intensify their courtship rituals for the more fecund females. Research has shown that males that mate with larger females do indeed receive and hatch greater numbers of eggs.[12]

Mating

Male bicolor damselfish, E. partitus, exhibit polygamy, often courting multiple females simultaneously. Among this species, evolutionary selection favors those males that begin mating as soon as possible during spawning seasons even if the most favorable egg clutches are spawned at later times. Females often choose which males to mate with depending on the males’ territory quality. Shelter sites are essential for the bicolor damselfish in avoiding predation, and females may evaluate the suitability of these sites at a male territory before depositing their eggs.[13]

Effect of distance on spawning

In the species S. nigricans, females usually mate with a single male each morning during spawning seasons. At dawn, they visit males’ territories to spawn. The distance to the territory of a mate influences the number of visits that a female undergoes with a male. At short distances, females make many repeated visits. At longer ones, they may spawn their entire clutch in one visit. This plasticity in mating behavior can be attributed to two factors: (1) intrusions by other fish to feed in the females’ territories while they are away, which could make the females return frequently to their habitats in order to defend their resources, and (2) predatory attacks on the females, which increase in frequency as the distances that the females travel become longer. Intrusion by other fish into a female’s territory can diminish the habitat of its food and render it unstable. Thus, a spawning female should return to its home as often as possible. However, a greater number of spawning visits increases the chance of being attacked, especially when mating with males that are far away. To minimize overall costs, females change their number of spawning visits depending on male territory distance.[14]

Filial cannibalism

The male cortez damselfish, S. rectifraenum, is known to engage in filial cannibalism. Studies have shown it typically consumes over twenty-five percent of its clutches. The males generally consume clutches that are smaller than average in size, as well as those that are still in the early stages of development. Female cortez damselfish tend to deposit their eggs with males who are already caring for early-stage eggs, rather than males with late-stage eggs. This preference is seen particularly in females that deposit smaller-sized clutches, which are more vulnerable to being consumed. For the males, filial cannibalism is an adaptive response to clutches that do not provide enough benefits to warrant the costs of parental care.[15]

References
  1. James Cooper, W.; Smith, Lydia L.; Westneat, Mark W. (2009). "Exploring the radiation of a diverse reef fish family: Phylogenetics of the damselfishes (Pomacentridae), with new classifications based on molecular analyses of all genera". Molecular Phylogenetics and Evolution. 52 (1): 1–16. doi:10.1016/j.ympev.2008.12.010. ISSN 1055-7903.
  2. "A Revised Damselfish Taxonomy with a Description of the Tribe Microspathodontini (Giant Damselfishes)", Biology of Damselfishes, Taylor & Francis Group, 6000 Broken Sound Parkway NW, Suite 300, Boca Raton, FL 33487-2742: CRC Press, pp. 13–30, 2016-07-31, ISBN 978-1-4822-1209-9, retrieved 2020-12-14CS1 maint: location (link)
  3. Hensley, Dannie A.; Allen, Gerald R. (1996-02-02). "Damselfishes of the World". Copeia. 1996 (1): 229. doi:10.2307/1446968. ISSN 0045-8511.
  4. Bellwood, David R.; Sorbini, Lorenzo (1996-06-01). "A review of the fossil record of the Pomacentridae (Teleostei: Labroidei) with a description of a new genus and species from the Eocene of Monte Bolca, Italy". Zoological Journal of the Linnean Society. 117 (2): 159–174. doi:10.1111/j.1096-3642.1996.tb02154.x. ISSN 0024-4082.
  5. Mann, David A.; Gorka Sancho (10 September 2007). "Feeding Ecology of the Domino Damselfish, Dascyllus albisella". Copeia. 3 (3): 566–576. doi:10.1643/0045-8511(2007)2007[566:feotdd]2.0.co;2.
  6. Williams, Ann Houston (1978). "Ecology of threespot damselfish: Social organization, age structure, and population stability". Journal of Experimental Marine Biology and Ecology. 34 (3): 197–213. doi:10.1016/S0022-0981(78)80002-1.
  7. Bartels, Paul Jon (1984). "Extra-Territorial Movements of a Perennially Territorial Damselfish, Eupomacentrus Dorsopunicans Poey". Behaviour. 91 (4): 312–321. doi:10.1163/156853984X00137. ISSN 0005-7959.
  8. Brooker, Rohan M. (7 December 2020). "Domestication via the commensal pathway in a fish-invertebrate mutualism". Nature Communications. 11: 6253. doi:10.1038/s41467-020-19958-5.
  9. Knapp, Roland A.; John T. Kovach (1991). "Courtship as an honest indicator of male parental quality in the bicolor damselfish, Stegastes partitus". Behavioral Ecology. 2 (4): 295–300. doi:10.1093/beheco/2.4.295.
  10. Knapp, Roland A.; Robert R. Warner (May 1991). "Male parental care and female choice in the bicolor damselfish, Stegastes partitus: bigger is not always better". Animal Behaviour. 41 (5): 747–756. doi:10.1016/s0003-3472(05)80341-0.
  11. Mann, David A.; Phillip S. Lobel (15 February 1997). "Propagation of damselfish (Pomacentridae) courtship sounds". The Journal of the Acoustical Society of America. 101 (6): 3783–3791. Bibcode:1997ASAJ..101.3783M. doi:10.1121/1.418425.
  12. Itzkowitz, M.; M. J. Draud; J. L. Barnes; M. Haley (March 1998). "Does It Matter That Beaugregory Damselfish Have a Mate Preference?". Behavioral Ecology and Sociobiology. 42 (3): 149–155. doi:10.1007/s002650050425.
  13. Schmale, Michael C. (November 1981). "Sexual selection and reproductive success in males of the bicolor damselfish, Eupomacentrus partitus (Pisces: Pomacentridae)". Animal Behaviour. 29 (4): 1172–1184. doi:10.1016/s0003-3472(81)80069-3.
  14. Karino, Kenji; Tetsuo Kuwamura (1997). "Plasticity in Spawning Visits of Female Damselfish, Stegastes nigricans: Effect of Distance to Mates". Behavioral Ecology and Sociobiology. 41 (1): 55–59. doi:10.1007/s002650050363.
  15. Petersen, Christopher W.; Karen Marchetti (January 1989). "Filial cannibalism in the Cortez Damselfish stegastes rectifraenum". Evolution. 43 (1): 158–168. doi:10.2307/2409171.
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