The list was subsequently mapped to 5,506 zebrafish Unigene clusters. The 5,506 zebrafish Unigene clusters identified in the swimbladder were classified based on Gene Ontology (GO). Comparing to the distribution of GO categories of the total ZGC database (9,631 Unigene clusters), the swimbladder had significantly more expressed genes with unknown function in all the three classifications: Biological Process, Molecular Function, and Cellular Component, indicating the fact that the swimbladder is a less studied organ (Figure 3, Table S2). Under the Biological Abmole LY294002 Process classifications, large proportions of genes were involved in housekeeping functions such as metabolic process and biological regulation. In Molecular Function classification, the categories of nucleotide binding and structural molecular activity were significantly enriched in the swimbladder, whereas in Cellular Component classification genes functioning in the endoplasmic reticulum was enriched in the swimbladder, suggesting the order BAY-60-7550 active synthesis and transportation of proteins. In particular, enriched categories under Molecular Function and Cellular Component together implicated the abundance of cytoskeleton genes in the swimbladder. Next we compared the Gene Ontology and energy distribution of the swimbladder under Molecular Function category. Energy distribution describes how a given tissue distributes its transcriptional energy based on relative abundance of total transcripts in different GO groups, thus yielding information on the main function of the tissue. As shown in Figure 4, genes with nucleotide binding function are the second most diversified group in the swimbladder, and this group occupies a much heavier proportion in the energy distribution, indicating these transcripts tend to have higher expression levels. At the same time, there were a few categories which showed high diversity but have low expression levels, including genes with hydrolase, transferase, transcription regulator, molecular transducer, and enzyme regulator activities. These categories are crucial for maintaining basic metabolisms and performing specific functions for the swimbladder, although they are expressed at relatively lower levels.