Reproductive biochemistry of Chinook Salmon (Oncorhynchus tshawytscha)
A female fish has a finite amount of resources to invest in a given episode of reproduction; therefore, she must resolve a trade-off between investing more into each egg versus making more eggs. Due to the importance of egg size on offspring survival, studies suggest that a female should alter the number of eggs she produces, rather than decreasing each egg's chance for survival by altering egg size. These trade-offs are resolved differently by different species, such that, theoretically, there is an optimal egg size for every spawning situation.
To achieve an optimal egg size there should be an optimal amount of developmental material placed into each egg. In fact, studies assume that a larger egg contains more developmental material yet few have studied the relationship. Developmental materials include protein and lipid. Here, three hypotheses were proposed and evaluated: a) larger eggs will have more protein, b) larger eggs will have more lipids, c) protein and lipid quantities will increase at the same rate with increases in egg size.
Studies also assume that females with increased resource availability will have larger eggs with more developmental material. One reproductive molecule largely responsible for egg growth is vitellogenin. Here, four hypotheses were proposed and evaluated: a) egg size will increase with vitellogenin, b) egg protein will increase with vitellogenin, c) egg lipids will increase with vitellogenin, and d) egg size, egg protein, and egg lipids will increase at the same rate with increases in vitellogenin.
For all eggs being tested, egg size was determined using effective diameter, as well as egg weight. Egg protein quantities were determined for individual eggs using a modified Lowry Assay. Egg lipids were extracted from individual eggs using a 2:1 mixture of chloroform: methanol and lipids were weighed gravimetrically. The results indicated that there was variation in egg size and egg components within one female; however, there was no relationship between either egg protein or egg lipid and egg size within the females sampled. Similarly, there was egg protein, egg lipid and egg size variation across females; however, there was only a positive relationship between egg protein and egg size across females with larger eggs containing more protein. The relationship between egg lipids and egg size across females was inconclusive.
For comparison of egg size and egg components to vitellogenin, both egg protein and egg lipids were determined for each female. Along with egg samples, blood was taken from the caudal vein of each female and relative vitellogenin quantification was performed using a commercial Rainbow trout EIA kit. There was no relationship between any of the egg parameters investigated and circulating female vitellogenin.
Holland, Erika Beth (2008) Reproductive Biochemistry of Chinook Salmon (Oncorhynchus tshawytscha). Masters thesis, Department of Biological Sciences, California State University, Sacramento.
Erika joined the lab in Fall of 2005 and finished in May of 2008.
Erika is now pursuing her PhD at UC Davis in the lab of Dr. Inge Werner