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Thomas Wetherill Literature Review Due to their environmental adaptations and intricate feeding and mating, seahorses are one of the many species that are adversely affected by overfishing and habitat change (Oliveira, T.P.R et al. 2010; Foster, S.J & Vincent, A.C.J. 2004). In the captive rearing of seahorses it has been found that factors such as background colour and sound can drastically effect the mortality rate with some colours causing increased mortality and some sounds stunting growth which shows how changes from the norm can drastically effect population both captive and in the wild, small changes in stress can vastly affect breeding potential and population globally if environmental problems become widespread (Pawar, H.B. 2011; Berzins, I.K et al. 2010). According to Teske, P.R & Beheregaray, L.B. 2009, seahorses are thought to have diverged from pipefish during the late Oligocene period around 20 million years ago (Casey, S.P et al. 2004). The seahorses’ habitats, generally sea grasses in shallow waters were greatly increased allowing for the evolution of the upright position which would have been favoured in the new habitat without affecting speed or the ability to remain camouflaged. The pipefish, however never entered this new habitat so there was no evolutionary need to evolve into an upright position meaning they maintained their horizontal body shape like the majority of fish found in the ocean. Syngnathids move using the dorsal and pectoral fins which beat at a high frequency enabling movement in the water, generally seahorses can beat their fins at a higher rate than pipefish so can move faster (Ashley-Ross, M.A. 2002). The Long-snouted seahorse, Hippocampus reidi, is one of the most sought out species in the international aquarium trade (da Hora, M.D.C. 2009; Diniz, A.D. 2008; Luiz, A et al. 2008; Rosa, I.L. 2006). Seahorses, along with pipefish, form the family Syngnathidae which are categorised by male pregnancy (Hoffman, E.A. 2006). The only genus in that family is Hippocampus (Freret-Meurer, N.V & Andreata, J.V. 2008; Salin, K.R et al. 2005; Silveira. 2000). The female carries the eggs until courtship and mating occurs, in which time the eggs are transferred to specialised brooding pouches located on the tail or abdomen of the male seahorse. The courtship dance and mating can last for several days. All post fertilisation care such as nourishment and osmoregulation is taken care of by the male which has evolved morphological traits to do this (Wilson, A.B. 2004). Like all species of the Syngnathid family, the young are born as miniature replicas of the adult and increase in size when they mature rather than change appearance (Garrick-Maidment, N. 1998). Roos et al, 2009 stated that Hippocampus reidi, like all Syngnathid fish, have a very morphologically different method of feeding compared to other fish. Whilst other fish feed by creating an anterior to posterior flow of water in their expandable head to create suction in a uni-directional direction, seahorses utilize their mouths to make rapid sucking movements close to the prey in order to feed. The maximum flow velocity is not found in the mouth channel, like with most teleosts, but rather in the narrow channel in the buccal cavity. They have specialised features such as elongated snouts and an immobile pectoral girdle which allows for this to occur (Leysen, H. 2011). They are visual feeders in that they have to see their prey before they hunt it rather than relying on scent or chemical indicators like some fish (Lee, H.R & O’Brien, K.M.D. 2011). Hippocampus reidi, when studied in the wild, have been found to be rather sedentary predators waiting for their prey to come to them most of the time rather than stalk them (Felicio, A.K.C. 2006). Their colour varies Word Count: 1900 December 2011 Thomas Wetherill massively from black, yellow, orange, brown and red with numerous white dots all over but mainly the tail area. Research into seahorse populations have led to the focusing on different management procedures that could be put in place to ensure the conservation of the species (Lourie, S.A et al. 1999). Seahorse populations are a cause for concern due to the vast market for various uses for them. All seahorses are listed on CITEs as vulnerable on the red list of endangered species in the International Union for the Conservation of Nature. This puts severe restrictions on the export and import of all seahorses, alive or dead which dramatically helps in seahorse conservation as global fishing will reduce as the available market decreases as well as helping to eliminate the wild seahorse trade in the aquarium trade. (IUCN, 2008; Olivotto, I et al. 2008). They are a popular ornamental species as well as being traded to be used in various traditional medicines, remedies and other product forms in various cultures around the world in high volumes (Zhang, D. 2010; Oliveira, T.P.R et al. 2007; Woods, C.M.C. 2007; McPherson, J.M & Vincent, A.C.J. 2004; Payne, M.F & Rippingale, R.J. 2000). They are targeted by divers that visit areas high in sea grasses and corals and are commonly poached along with sea cucumbers and a number of different gastropods (Salin, K.R et al. 2005). This overlong unsustainable exploitation of the seahorse species has caused vast gaps in our knowledge of their biology and ecology due to them becoming increasingly difficult to find (Woods, C.M.C. 2002). This is not helped by the gradual degradation and destruction of their habitats in coastal areas including coral reefs, sea grasses and mangroves (Olivotto, I et al. 2008). Hippocampus reidi are generally found within the tropics globally and are actively fished in some parts of the world namely the southern American countries such as Brazil where they have the common name, Brazilian Seahorse (Rosa, I.L et al. 2005). They have also been found in Guatemala, Honduras, Mexico, Nicaragua and Panama. Fisherman in those areas have reported a general decline in all seahorse species caught as by-catch in trawling and live subjects captured by divers. Hippocampus reidi have been found at depths as deep as 55m so are not thought to be as affected by accidental by-catch as some other species of seahorse but are thought to be equally susceptible to environmental changes to their habitats (IUCN. 2008). In 175 countries the export of seahorses has been limited to sustainable levels now in place to help protect them and also allow their numbers to replenish (Vincent, A.C.J et al. 2011). When keeping seahorses in captivity various problems can arise due to problems with feeding and disease. Fortunately aside from temperature “most seahorse species have very similar requirements when kept in captivity” (Baldwin, C. 06/12/2011). This allows for feeds that can be fed to all Hippocampus species universally. When in a juvenile state many seahorse species have a low survival rate unless fed the correct live foods and kept in an immaculate environment to reduce the risk of disease. A typical live feed that is often used is the zooplankton species artemia nauplii, however if it is entirely utilised there is often a poor juvenile survival rate as the species stop feeding (Lunn, K.E & Hall, H.J. 1999). Despite not being a natural food source for most species it has been successfully used for many years though not with a 100% success rate (Rimmer, M.A et al. 1994; Sorgeloos, P. 1987). It can also be enriched with highly unsaturated fatty acids (HUFAs) which make them very suitable for juvenile fish and syngnathids as they require live foods with a high nutritional content and most can feed on the same day they leave the adult males pouch (Sargent, J.R et al. 1997; Watanabe, T et al. 1983). Other live prey that seahorses feed on includes rotifers, mysid, shrimp and copepods (Woods, C.M.C. 2002; Payne, M.F & Rippingale, R.J. Word Count: 1900 December 2011 Thomas Wetherill 2000). Rotifers and artemia nauplii are generally the favoured though due being able to be easily cultured in large quantities (Otero-Ferrer, F et al. 2010; Olivotto, I et al. 2008). Chang, M.C, 2000, stated that most of the strains of artemia found in the aquatic sense are deficient in HUFAs making them a poor long term food source for many fish species. By allowing them to ingest food rich in HUFAs prior to their introduction into the diet of the cultured fish species, they become enriched in fatty acids essential for growth and development. They are one of the most cultured live food sources used in the aquacultural world. During a study conducted by Chang, M.C 2000, the highest and quickest mortalities were observed in the non-enriched artemia feeding group, once again showing the lack of nutrition that can be obtained from using ordinary artemia as a long term standard feed. Studies into enrichment have shown a usually substantial decrease in species mortality for most fish when an enriching agent such as cold liver oil or squid oil has been fed to artemia prior to their feeding to the fish (Southgate, P.C & Kavanagh, K. 1999). Another increasingly popular method of enriching agent is selco, a slurried fish meal based product that is fed to artemia and other zooplankton for enrichment and is very high in essential fatty acids (Woods, C.M.C. 2002). There are typically two commercial strains of artemia that are used; the ‘marine’ species which are generally more expensive as well as being smaller in size with a larger nutritional profile, and the ‘continental’ species which is cheaper as well as being larger with a poorer nutritional profile (Mendes, A.C et al. 2010). In order to maintain water quality and help minimise excess waste products such as nitrogenous waste it is important to regulate the food intake of the cultured species. It is now commonly acknowledged that fish aren’t the polluters but rather excess food and over feeding is the leading contributor to waste; either faecal matter or decomposing organic matter (Amirkolaie, A.K. 2011). Excess levels of ammonia, even milligrams too much can cause long term damage to many species and can increase potential stress. The optimum level of ammonia in a closed system is zero milligrams per litre so it is very important to continually monitor water quality after feeding the species as that is when the waste levels will be highest so will give a more accurate reading of the exact amounts of ammonia and other nitrogenous waste in the system. If water quality shows that the levels of ammonia have risen above 0.02 milligrams per litre it is essential that a water change is performed as the levels can change quickly and the higher they rise the more likely it is for damage and stress to occur (Forteath, N. 2001). The short-snouted seahorse, Hippocampus hippocampus, is a native British seahorse that is one of only two species known to occur in Northern Europe (Pinnegar, J.K. 2008). The other is the spiny seahorse, Hippocampus guttulatus. Both of these species are seagrass dwelling, spending the warm summer month inhabiting the eelgrass beds around the UK and then migrating in the cooler months to the boulders and rocks in slightly deeper waters (Garrick-Maidment, N. 1998). In the Falmouth estuary in Cornwall there has always been rumours of a secret hotspot of seahorses due to the eelgrass beds present (Deeble, M & Stone, V. 1985). Seahorses have always held a special place in peoples’ hearts because of their interesting and aesthetically pleasing appearance and their historical aloofness which means that many people would want to help boost their numbers especially as their population is hard to predict due to their migrations into different water depths and ability to camouflage well (Garrick-Maidment, N. 1998). Researching the essential foods that are most beneficial to the seahorses when reared in captivity is an important investigation due to its’ potential to lead to the rerelease of bred native species back into the estuary to boost their numbers. In order to be able to get permission to rear native seahorses, experience is Word Count: 1900 December 2011 Thomas Wetherill needed raising non-native that are not under the protection of the Wildlife and Country side Act 1981 that was amended in 2008 to prevent the killing, injuring or taking of Hippocampus hippocampus or Hippocampus guttulatus (Natural England. 2009). The rearing of a nonnative species such as Hippocampus reidi for a period of time in which a feed trial of different foods would be tested on separate test groups would be a good way to find the most beneficial foods for growth and development and also for any bodies hoping to acquire a licence for keeping natives in the future to gain experience. Word Count: 1900 December 2011