The toxicities of several oil dispersants (solvent emulsifiers or 'detergents,) to the young stages of six species of commercially important marine fish, haddock, herring, lemon sole, pilchard, plaice and sole, have been examined. Details of the laboratory rearing and maintenance of the embryos and larvae of, those species are given. The chemical nature of dispersants and their behaviour in sea water are discussed in relation to toxicity testing. The main factors influencing the acute toxicity of a dispersant were the type and aromatic content of the solvent. Newer dispersants using straight chain alcohols or Water as solvents had very low toxicities. Ageing of dispersant solutions led to a marked decrease in toxicity and this decline could be related to the loss of aromatics from solution by evaporation or degradation. Temperature and salinity had only slight influence on toxicity. For all dispersants differences, of susceptibility between species wore less than differences at different ages within a species. The larvae of all species showed a similar susceptibility when newly hatched but the embryos (within the chorion) wore more resistant. Susceptibility increased throughout the yolk-sac stage and a similar increase was observed when feeding larvae were starved. The transition period from yolk reserves, to an external food supply Was most critical for once larvae had established feeding resistance increased up to metamorphosis. The dispersants appeared to act largely as physical toxins causing, initially at least, e reversible narcosis, Criteria other than survival were used to determine the presence and persistence of sub-lethal toxication. Treatment of developing embryos with dispersants gave rise to abnormalities in cell division, heart rate, eye pigmentation, growth rate and hatching success but did not affect the length of the incubation period. The treatment produced larvae with abnormal flexures of the spine which prevented the larvae from feeding successfully. Feeding experiments demonstrated that in the presence of sub-lethal concentrations the ability of larvae to capture food wan impaired. After returning to clean water they recovered but remained consistently less successful at food capture than untreated larvae. However plaice larvae reared to metamorphosis after a sub-lethal dosing showed no differences in survival, size condition or pigmentation when compared with controls. By using a thermistor technique to monitor activity it was possible to determine the effects of dispersants on the normal phototactic behaviour exhibited by larvae at high and low light intensities. Initially the dispersants caused an enhanced response but with continued exposure the activity of the larvae declined and a breakdown in the negative, then the positive phototaxis followed. Behavioural aberrations were detected at only one hundredth of the lethal concentration. The larvae quickly recovered the normal behaviour pattern when transferred to clean water. Larvae did not exhibit a chemotactic response to horizontal gradients of dispersants generated in a fluvarium but because the dispersants increased their swimming activity the larvae exhibited an avoidance of potentially lethal concentrations. Similarly the larvae swam into dispersants in horizontal gradients. They remained in high concentrations until they became narcotized when they sank into clean water and recovered. The ecological significance of the lethal and sub-lethal effects of dispersants on the eggs and larvae of marine-fish and the problems of extrapolation of laboratory results to field situations are discussed in the light of possible effects on future stock and recruitment.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:593830 |
| Date | January 1975 |
| Creators | Wilson, K. W. |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU404940 |
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