Abstract
Elasmobranchs are one of the oldest families of animals on Earth, dating back 400
million years. These animals are also known as Chondrichthyes which mean they are
cartilaginous fish, as they have no bones in their bodies. Sharks and ray are iconic
animals in the oceans as they play a vital role in the food web. Certain species of
elasmobranchs are top food chain predators and can serve as ocean health indicators.
Elasmobranch stocks are of important eco-tourism and economic value i.e. shark cage
diving, aquariums, protein, cosmetic and petfood products. Recently sharks and rays
have become the most threatened group of chordate species due to anthropogenic
factors such as overharvesting, illegal fin trade, ray gill raker trade, pollution, meat
trade and by-catch.
Currently the health and reproductive status of many elasmobranch species are not
known or limited information and data is available. Pollutants such as heavy metals,
plastics, pesticides and pharmaceutical have been known to bioaccumulate and
biomagnify within shark and ray species. These xenobiotics could possibly alter the
health and reproductive structures of elasmobranchs. Histology and histological
alterations of important organs and ultrastructure of gametes have been used
successfully to determine the health and reproductive status of various species.
The critically endangered scalloped hammerhead (Sphyrna lewini) forms part of the
family of Sphyrnidae with eight other species of which the smooth (Sphyrna zygaena)-
and great hammerhead (Sphyrna mokarran) are also found along the subtropical and
warm temperate coastal line of South Africa. The scalloped hammerhead served as
one the study species for this study. The near threatened spinner shark (Carcharhinus
brevipinna) forms part of the family Carcharhinidae with several other species which
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are found along the subtropical and warm-temperate waters of South Africa's coastal
line. The near-threatened spotted eagle ray (Aetobatus narinari) forms part of the
family Batoidea and is also found along the subtropical and warm-temperate waters
of South Africa's coastal line. These species also served as a study species for this
project.
The aim of the study was to do a histological assessment of selected target organs
(testes, liver and kidney) of Sphyrna lewini, Carcharhinus brevipinna and Aetobatus
narinari from the KwaZulu-Natal coastal line.
The sampling of the different study species took place in KwaZulu-Natal, South Africa.
The KwaZulu-Natal Sharks Board (KZSNB) provided the study species as part of the
bather protection programme were the samples were obtained as by-catch. Standard
necropsies was done for all the specimens in order to identify any external or internal
macroscopic abnormalities, as well as to obtain biometric data. Specific target organs
such as the liver, testes and kidney were sampled and fixated in Bouin's solution and
neutrally-buffered formalin respectively. These samples then underwent dehydration
in ethanol (30%-100%), clearing in xylene and embedding in paraffin wax. The wax
blocks were sectioned and mounted onto microscope slides. The sections were
stained with H&E, PAS and Azan Trichrome respectively. The sperm were also
sampled from the scalloped hammerhead and fixated in Karnovsky's solution and
processed for scanning electron microscopy (SEM) and transmission electron
microscopy (TEM). Assessment of the slides took place with light microscopy and
electron microscopy to explore the spermatogenic stages of the shark. A semiquantitative
histological assessment was done on selected target organs. Liver and
muscle samples were also collected for bioaccumulation analyses. Historical biometric
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data was also obtained from the KZNSB for analyses. Exploratory statistics was done
using Principle Component Analysis (PCA).
The results provide the first description of spermatogenesis for the diametrical testes
of S. lewini from South Africa. It was found that the spermatogenesis process comprise
of seven stages and conforms with the stages that were described for other species.
The spermatogenic stages of C. brevipinna and A. narinari were also identified and
described for the species from South Africa.
The histology of the liver, testes and kidneys were also described for the three different
species. Various types of histological alterations were identified within the liver, testes
and kidney tissues such as melano-macrophage centres, lipid accumulation,
nephrocalcinosis, hyperplasia and hypertrophy of Leydig cells and perivascular mononuclear
aggregates. The results also showed detectable levels of polychlorinated
biphenyls, mercury, arsenic, lead and cadmium in the liver and muscle tissue of the
different study species. In the limited histological studies done on the liver, testes and
kidney of elasmobranchs, histological alterations that were found could be attributed
to the presence of anthropogenic pollutants.
The ultrastructure assessment of the spermatozoa of S. lewini showed that the
spermatozoa morphology conformed to what has been previously described with the
identification of a distinct headpiece, midpiece and tailpiece.
In conclusion the histological analyses of the selected target organs of the sampled
species showed similar microscopic structure and stages of spermatogenesis
compared to what has been described for other elasmobranch species. Histological
alterations were identified in the selected target organs, and liver and muscle tissue
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of the sampled specimens had high levels of bioaccumulated organic and inorganic
substances.
The importance of this study was to expand the limited knowledge that is currently
available regarding reproduction and health status of the scalloped hammerhead, the
spinner shark and the spotted eagle ray, thus by providing baseline data which could
be essential for future studies on the species. By investigating the health status of
these species along the eastern South African coastline, valuable insight is provided
on the effect pollutants can have on these endangered species. Due the fact that one
of these species are critically endangered and the others are near-threatened, it is
important that better legislation on environmental pollution and law enforcement is
needed.