Mechanisms of maintenance of tropical freshwater fish communities in the face of disturbance.

Community resistance to, and resilience from, perturbation will determine the trajectory of recovery from disturbance. Although selective timber extraction is considered a severe disturbance, fish communities from headwater streams around Danum Valley Field Centre, Sabah, Malaysia, showed few long-term changes in species composition or abundance. However, some species showed short-term (< 18 months) absence or decrease in abundance. These observations suggested that both resistance and resilience were important in maintaining long-term fish community structure. Resistance to perturbation was tested by monitoring fish communities before and after the creation of log-debris dams, while resilience was investigated by following the time-course of recolonization following complete removal of all fish. High community resistance was generally shown although the response was site-specific, dependent on the composition of the starting community, the size of the stream and physical habitat changes. High resilience was demonstrated in all recolonization experiments with strong correlations between pre- and post-defaunation communities, although there was a significant difference between pool and riffle habitats in the time-course of recovery. These differences can be explained by the movement characteristics of the species found in the different habitats. Resilience appeared to be a more predictable characteristic of the community than resistance and the implications of this for ensuring the long-term persistence of fish in the area are discussed.

Role of autoantibodies in the autoimmune response to testis in rainbow trout (Salmo gairdneri).

Rainbow trout, Salmo gairdneri, passively immunized with anti-sperm antibodies developed lesions in the testis characteristic of autoimmune attack. Only animals pre-treated with Freund's complete adjuvant developed these lesions. Investigations into the possible role of autoantibodies during autoimmune attack, carried out in vitro, showed that sperm antibodies were not cytotoxic but did have an opsonic effect on macrophage phagocytosis of sperm in the presence of complement.

Field trials of a method of induction of autoimmune gonad rejection in Atlantic salmon (salmon salar L.).

Autoimmune gonad destruction was induced in Atlantic salmon of both sexes in trials carried out on fish kept in sea cages on a fish farm. Damage to gonads was only found in fish where the first injection of gonad extract had been given together with Complete Freund's Adjuvant, injections without adjuvant or with carrageenan as an adjuvant were unsuccessful. Length and weight differences between treated and untreated groups of fish were slight at the termination of the experiment. Results suggest that practical application of this technique would involve injection at an early stage of gonad development and at a higher water temperature (greater than 10 degrees C) to increase the rate of the primary autoimmune response. The lesion induced in the salmon testis was compared with that caused by autoimmune destruction of mammalian testis.