Biochemical mechanisms regulatin sperm functions in fish

Spermatozoa of teleost fish are important cells under biotechnological aspects. They play a key role for artificial fertilization which due to water pollution and exploitation of fish stocks is a very important technique to maintain population size. They are also suitable as models for toxicological tests, as they react sensitive to several types of environmental pollutants. Further they have importance for cryopreservation and subsequent gene banking. However, the work with spermatozoa of teleost fish is difficult, as the sperm motility and fertility in comparison to mammals is very short (30 - 120 sec) and also in non-activated, immotile semen changes occur within 1 - 2 h after collection (= semen aging) which restrict its liquid storage. Basic knowledge about semen biology of teleost fish, especially about the biochemical mechanisms regulating sperm functions would be necessary for optimisation of the mentioned biotechnologies. Therefore, the proposed project investigates the role of the organic fraction of the seminal fluid for sperm physiology and metabolism to obtain exact knowledge about the biochemical mechanisms regulating the sperm functions in teleost fish. The data obtained in the project will have a benefit for general biochemistry and cell biology in understanding regulatory processes in sperm cells. The results of the project will serve as basis for future application in aquaculture, cryopreservation and gene banking, and development of toxicological tests for aquatic organisms substituting the acute animal test. The project is conducted in a comparative way on different species of fresh water (Salmonidae, Cyprinidae) and marine species (Sparidae) and according to the following design: From previous studies it is known that organic compounds of the seminal fluid stabilize the sperm functions in a very significant way. However, the exact components and molecules are unknown. Therefore, seminal plasma organic compounds are analyzed, extracted and added to sperm motility inhibiting saline solution or sperm motility activating saline solutions. The effect of the compounds on sperm physiology (motility, fertility, membrane integrity, respiration rate) and on sperm metabolism (system involved in energy production, sperm axonemal dynein ATPase system, system for regulation of sperm motility) is investigated. The investigation of rate limiting pathways in spermatozoa is an important additional part of the project which has the goal to find possibilities for prolongation of sperm motility and sperm viability.

Teleost fish are animals with external fertilization. Spermatozoa are released into water where they can survive for only some minutes. Therefore, these cells are very simple constructed. Due to their simple organization the work with fish spermatozoa is difficult, as the sperm motility and fertility in comparison to mammals is very short (30 - 120 sec) and also under optimised conditions spermatozoa of most species can only survive for some hours. Nevertheless spermatozoa have important meanings under biotechnological aspects. They play a key role for artificial fertilization, which due to water pollution and exploitation of fish stocks is a very important technique to maintain population size. They are deep frozen (cryopreserved) to conserve the genetic material of endangered fish species or populations from extinction. They could become also models for ecotoxicological tests, as they react sensitive to several types of environmental pollutants. For all these works and manipulations it is necessary to stabilize and increase the viability of fish spermatozoa. In this project we analysed the composition of the seminal fluid, the fluid where the spermatozoa are stored within the fish organism and which is known to have positive effects on the sperm fertility. Specific organic compounds were defined which have a positive effect on sperm viability and which can prolong it for significant time periods. When these components are added to the sperm storage solutions to produce an artificial seminal fluid the fertility can be increased and the viability prolonged for considerable time spans which has beneficial aspects under the above mentioned aspects.