Siganus sutor

Siganus sutor, the shoemaker spinefoot rabbitfish, is a species in the family Siganidae.[2] It is also known as whitespotted rabbitfish and lives in Indo-Pacific coral reefs.[3] It is endemic to the Indian Ocean, from Indonesia to Comoros.[4] S. sutor is one of the commercial marine fishes, which is ubiquitously caught, in Tanzania and the entire East African coast of Indian ocean.[5] S. sutor is among the most common fish species in the marine fisheries of Kenya, and accounts for around 40% of the artisanal fishery landings.[6] Various fishing gears are used to target the siganids, but basket traps are the preferred ones.[7] It is one of the mangrove/seagrass-associated coral reef fishes.[5] This species inhabits littoral areas and its fin spines are venomous to humans.[4]

Siganus sutor
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Perciformes
Family: Siganidae
Genus: Siganus
Species:
S. sutor
Binomial name
Siganus sutor
(Valenciennes, 1835)

Behavior and habitats

Wild siganids have diurnal schooling behavior and feed in shallow water habitats.[8] They inhabit in inshore areas, particularly in seagrass beds and coral reefs (when they are adults).[5] The depth range of the living habitat is from 1m to 50m, but usually from 1m to 12 m.[9] When S. sutor is threatened, it will raise its dorsal fin for protection.[10] Also, S. sutor returns to the same offshore coral patch reef aggregation site to spawn on subsequent full moons, migrating at most 3.3 km from fishing grounds closer to shore.[6]

Diet and feeding feature

Siganus sutor is an herbivore, which feeds mainly on macro-algae.[5] It is a diurnal feeder, but it is often seen out in the open sea on night dives off the Tanzanian coast.[10]

Description

The maximum reported age for Siganus sutor was 3 years old. The color patterns of the fish extend to the fins.[9] During the daytime, the body of the S. sutor is usually a silver color with white spots. Sometimes there would be blue spots within the white spots. During night time, the fish has a mottled green or grey color. Siganus sutor has the ability to immediately change between these two color patterns.[10] The spines of the Siganids are slender, pungent and venomous.[9] Venom glands in the spines can cause great pain but are unlikely to be fatal to a healthy adult.[10] S. sutor has a total of 13-14 dorsal spines, 10 dorsal soft rays, 7 anal spines, 9-10 anal soft rays and 23 vertebraes. Long flap of anterior nostril shortens as the fish ages.[9]

Venom treatment

If a person is envenomated by the spines of Siganus sutor, the treatment is to use hot water (as hot as one can take) for 60 to 90 minutes.[10]

Parasitism

Siganus sutors are likely to have gill parasites, such as the monogeneans Psedohaliotrema sp., Tetrancistrum sigani and Microcotyle mouwoi, the copepods Hatschekia sp., Psedolepeophtheirus sp. and juvenile Caligidae, and prazina larvae of the isopod Gnathia sp. Compare to the subadults, adult siganids would have higher parasite load, and the juvenile siganids do not have any gill parasites.[11]

Reproduction

The two spawning seasons for Siganus sutor are January/February and May/June.The presence of these seasons is determined by three factors: (1) temporal changes in the condition factor and relative weight of the gonads, (2) the progression of peaks of maturity stages with seasonal presence of spent fish in the samples, and (3) the seasonal appearance of juveniles.[12]

Siganus sutor and two other fish species (Lethrinus harak and Rastrelliger kanagurta) had been used to study the bioaccumulation of heavy metals in marine fishes from Dar es Salaam Tanzania. Researchers had assessed the potential risks to human health and the suitability of the fishes' fins as a non-destructive monitoring organ. The results showed that fins were not suitable as non-destructive monitoring organs for most metals. The levels of metal intake of aluminum, cadmium, copper, iron, lead and zinc in the muscles of the Siganus sutor were below the FAO/WHO maximum levels for contaminants and toxins in food for human consumption.[5]

Existing management regulations

Wildlife Conservation Society, Kenya Marine and Fisheries Research Institute and State Department of Fisheries have promoted modification of the basket trap by adding an escape gap to help reduce the by-catch, which then allows the juveniles and small-sized fish to swim out of the trap.[7]

References
  1. Yahya, S., Borsa, P., Jiddawi, N., Carpenter, K.E., Obota, C. & Smith-Vaniz, W.F. 2018. Siganus sutor. The IUCN Red List of Threatened Species 2018: e.T117007332A117008798. https://dx.doi.org/10.2305/IUCN.UK.2018-2.RLTS.T117007332A117008798.en. Downloaded on 24 July 2020.
  2. [Agembe, S. (2012). "Estimation of important reproductive parameters for management of the Shoemaler Spinefoot rabbitfish (Siganus sutor) in Southern Kenya". International Journal of Marine Science. 2 (4): 24-30.]
  3. [Shirinabadi, M.; Matinfar, A.; Hosseinzadeh, H. (2013) "Effect of different light regimes on the maturational progress of the whitespotted rabbitfish (Siganus sutor)". Iranian Journal of Disheries Sciences. 12 (4): 916-927.]
  4. Fishbase
  5. [Mziray, P.; Kimirei, I.A. "Bioaccumulation of heavy metals in marine fishes (Siganus sutor, Lethrinus harak, and Rastrelliger kanagurta) from Dar es Salaam Tanzania". Regional Studies in Marine Science. 7: 72-80.]
  6. [Samoilys, M.; Kanyange, N.; Macharia, D.; Robinson, J.;Maina, G.W. Dynamics of rabbitfish (Siganus sutor) spawning aggregations in southern Kenya. In Reef Fish Spawning Aggregations in the Western Indian Ocean: Research for Management. Series 5; WIOMSA]
  7. [Kenya Marine and Fisheries Research Institute. http://www.kmfri.co.ke/index.php/fact-sheet/85-stock-assessment-of-rabbitfish-siganus-sutor-along-the-kenya-coast.]
  8. [Kamukuru, A.T. (2009) "Trap fishery and reproductive biology of the whitespotted rabbitfish Siganus sutor (Siganidae), within the Dar es Salaam Marine Reserves, Tanzania". Western Indian ocean J. Mar. Sci. 8 (1): 75-86.]
  9. [Fish Base. http://www.fishbase.org/summary/4615.]
  10. [Seaunseen. https://seaunseen.com/whitespotted-rabbitfish/]
  11. [Geets, A.; Coene, H.; Ollevier, F. (1997). "Ectoparasites of the whitespotted rabbitfish, Siganus sutor (Valenciennes, 1835) off the Kenyan Coast: distribution within the host population and site selection on the gills". NCBI. 115: 69-79.]
  12. [Ntiba, M. J.; Jaccarini, V. (1990). "Gonad maturation and spawning times of Siganus sutor off the Kenya coast: evidence for definite spawning seasons in a tropical fish". Journal of Fish Biology. 37: 315-325]
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