Learning about Shark Lifestyle – Studies from Preserved Samples

Telstar - Sample preparation. Freeze drying cells

The KwaZulu-Natal Sharks Board situated just north of Durban has been using a Telstar freeze dryer supplied by Labotec to preserve biological samples used for local and collaborative research.  Their work focuses on  stable isotopes  which are delivering interesting information on the presently little known food web interactions over ontogeny, the presence of retroviral DNA, and in the future, they will be looking at projects such as the shark specie’s sensitivity to mercury toxicity.  Debbie Shaw from Labotec spoke to Nomfundo Nkabi, Junior Scientist at the research centre about the exciting work happening now, as well as future planned studies involving the preserved biological samples.

Tell us more about the laboratory aims and objectives of the Sharks Board where the Telstar unit is situated?

The Telstar freeze dryer at the KwaZulu-Natal Sharks Board (KZNSB) is stationed in the wet laboratory where all sharks caught in shark safety gears are measured, sampled (i.e. taking various tissue samples for a number of research projects) and kept frozen for public dissection. The KZNSB is running a long-term monitoring collaborative stable isotope project; in the past years, it preserved more than 2000 tissue samples using an off-site freeze dryer. It is advantageous to have the machine in-house for us to meet project time frames.  We use it for preserving various biological samples requested by local and international researcher as part of collaborative research projects.

Please tell us more about the research happening in the laboratory.

Samples of shark muscle, liver and skin have been freeze-dried for stable isotope analyses. Sharks are large predators which are considered to feed at the top level of marine food webs. Although much is known regarding their feeding behaviour in coastal regions, little is known regarding their diet and food web interactions over ontogeny (developmental history within its own lifetime). In addition, limited work to date has investigated intra-population level variation in the diet and trophic position of the white shark. The stable isotopes of carbon and nitrogen provide tools to track both baseline productivity and relative trophic position of individual animals, respectively, and can also be used to provide information on niche width.

Samples of muscle were also freeze-dried for analyses of shark retroviruses. The literature suggests that sharks are remarkably resistant to viral infections, in part because there has been little noticeable pathology observed during studies of various shark species. However, there have been no molecular screens to detect viruses that are not causing visible disease.  The KZNSB is involved in this research by making the samples available, which enables UK researchers to identify whether retroviral DNA, from either endogenous or replicating retroviruses is present in a variety of different shark species.

Are there interesting future projects are on the cards?

The Telstar freeze dryer will be used by two interns from early next year for various internal stable isotope projects.

We will also be using it for a toxicology study, which will be focusing on determining the mechanisms and consequences of mercury demethylation in fish. The samples preserved will be used, to make predictions about species sensitivity to mercury toxicity.