The neglected diversity:
Blood Parasites of Catsharks off the Western Cape
Who would have thought that marine research, and specifically research on elasmobranchs (Elasmobranchii is a subclass of Chondrichthyes or cartilaginous fish, including the sharks and the rays, skates, and sawfish), would be one of the major areas of expertise in an inland university? Over the past three years, researchers at the NWU Potchefstroom campus, along with our collaborators at the South African Shark Conservancy (SASC) in Hermanus, have been doing research on elasmobranchs to determine ecotoxicity and their parasite diversity.
Southern Africa is known as one of the most biodiverse regions for chondrichthyans worldwide with over 200 reported species (Ebert and van Hees, 2015). The chondrichthyan diversity also encompasses catsharks of the family Scyliorhinidae, and they can be found in warmer seas worldwide and are often endemic to certain areas. They tend to live towards the bottom of the ocean from shallow depths to deep-water areas of 2000 m. Almost 90% of these sharks are oviparous, producing eggs all year round.
Eggs will attach to a substrate and the young hatchlings emerge looking like miniature adults (Weinheimer 2004). Three different species of shysharks can be found along the western coast of South Africa including the Brown shyshark, Dark shyshark, and the Puffadder shyshark. Along with the shysharks, two different types of catsharks can also be found including the Pyjama catshark and the Leopard catshark.
Shark Species Being Studied
1. Brown shyshark Haploblepharus fuscus Smith, 1950
The Brown shyshark, Haploblepharus fuscus, can be found along the coast from Cape Town to Mozambique, inhabiting sandy areas near the continental shelf (Shark Research Institute 2018). This small shark reaches approximately only 65 cm in length and can be identified by the brown colour with darker spots on the dorsal side. The diet of this species consists primarily of bony fishes and lobsters and when threatened will curl up with its tail over its eyes, hence the name shyshark (Shark Research Institute 2018). They are listed as Vulnerable by the IUCN due to their site-specific distribution close to the shore, threats include recreational fishing, habitat degradation and human utilization (coastal housing development and boating) of the habitat (Human 2009a). Little information is available on their population structure as these organisms are rarely caught and studied for their behaviour.
2. Dark shyshark Haploblepharus pictus Müller & Henle, 1838
Haploblepharus pictus, or commonly known as the Dark shyshark, is endemic to the coast of Namibia through to the cooler west coast of South Africa up until Port Elizabeth. This shark prefers kelp forest and rocky reef habitat where it preys upon crustaceans, molluscs, and bottom-dwelling fishes (Human 2009b; Two Oceans Aquarium 2018). Dark shysharks can be distinguished from Puffadder shysharks (see 2.1.3) by their more rounded snouts, depressed heads and large light spots on their dark body. This species is listed as Least Concern on the IUCN Red List but faces dangers of recreational fishing where survival rates of those released during catch-and-release fishing, is unknown, but considered relatively low (Human 2009b).
3. Puffadder shyshark Haploblepharus edwardsii Schinz, 1822
The Puffadder shyshark sometimes referred to as Happy Eddie, is found from Cape Point to northern KwaZulu-Natal (Human 2009c; Yeld and Smit 2006). These near threatened sharks prefer both the inshore and offshore waters of the continental shelf where they can feed on bony fishes, crustaceans and cephalopods (Carpenter 2018; Human 2009c). Considered Near Threatened by the IUCN, the number of individuals is declining possibly due to fishing pressure and habitat destruction caused by pollution and the inshore waters being disturbed by recreational diving and coastal housing development.
4. Pyjama catshark Poroderma africanum Gmelin, 1789
This shark, also known as the Striped catshark is endemic to South Africa and is restricted to the temperate waters of the Northern, Western and Eastern Cape provinces; however, it is most commonly found in the Western Cape (Compagno 2009). These near threatened sharks are characterised by the five to seven stripes on their dorsal side and live in the intertidal and subtidal zones and favour kelp beds during daytime and caves when resting. They prey on small marine organisms including cephalopods, crustaceans and bony fish (Compagno 2009). Due to unregulated near-shore fisheries, these sharks are often caught as bycatch causing their numbers to decline.
5. Leopard catshark Poroderma pantherinum Müller & Henle, 1838
The Leopard catshark is found along the entire coast of South Africa, Madagascar, Mauritius as well as Réunion Island. This shark can be found up to 50 m along rocky reefs and kelp forests in multiple fragmented populations. Due to this fragmentation, it is difficult to determine the state of the population (listed as Data Deficient by the IUCN) as well as the impact of possible threats (Human 2009d). Some of the possible threats these sharks face include residential and commercial development, pollution as well as biological resource use where they are often caught as bycatch and not released back again (Human 2009d).
With such high diversity and endemicity (i.e. 13 %) of shark species, the potential for discovering new parasites is large (Schaeffner and Smit, 2019). A parasite can be defined as an organism that lives in or on a host, often causing harm to the host by feeding on it or by obtaining food at the host’s expense (CDC 2016, Nordqvist 2016). Blood parasites, or haemoprotozoans, can be found infecting almost all vertebrate and invertebrate classes in both the aquatic as well as the terrestrial environment (Barta et al. 2012). Studies have mainly focused on the blood parasites infecting mammals, reptiles, and amphibians, however, in recent years interest in parasites infecting fish has also increased. Little is known on blood parasites infecting elasmobranchs worldwide, and knowledge on these parasites in South African cartilaginous fishes is even more limited. Even though blood parasites have been reported infecting two catshark species off the coast of the Western Cape of South Africa, only one of these has been formally described, Trypanosoma haploblephari (Yeld and Smit, 2006).
Furthermore, descriptions are based entirely on the morphology of the blood stages of these parasites. At a microscopical level, the available characters that may be used to differentiate parasite species are limited, and as such we cannot rely on morphological characteristics alone. Additionally, some species of trypanosomes are known for pleomorphism (having more than one form), which limits the use of morphological characters for differentiation even more. Over the last decade, there has been an increased effort to use molecular characteristics to help better differentiation of these parasites. However, until recently, this effort has been largely focused on the blood parasites of other vertebrate groups (mammals, birds, reptiles, and amphibians). With these groups, the combined use of both morphological and molecular characteristics has greatly aided in determining the identity and taxonomy of these elasmobranch blood parasites in relation to other marine and freshwater parasites, which in turn aided in assessing their biodiversity. These parasites are transmitted to the host via haematophagous (blood-feeding) vectors such as leeches or gnathiid isopods (Davies & Smit 2001). Within the framework of this project, we will assess the species diversity of blood parasites infecting near-shore catsharks off the Western Cape. By collecting and drawing blood from various species of catsharks (dark shyshark, puffadder shyshark, leopard catshark and pyjama catshark), we will be able to provide both morphological and molecular information of these parasites, aiding in formal descriptions, phylogenetic placement and thus taxonomic identity, which will assist in determining their biodiversity in these catsharks. This will lay the foundation for further research on blood parasites parasitising sharks off South Africa. It also highlights the need for a greater focus on the shark blood parasite fauna, a currently neglected group of parasites.
by Chantelle Pretorius
Water Research Group
Unit for Environmental Sciences and Management