Chapter 7: Cleithra, Dentaries, and Other Bones
Matthew D. Faust and George D. Scholten
The most common method of obtaining age estimates of fishes is interpretation of calcified structures (Casselman 1987; Quist et al. 2012), with scales, fin rays, and otoliths being most frequently used by management agencies (Maceina et al. 2007). However, these often-used calcified structures have limited application for age estimation of some fishes due to an inability to produce accurate and (or) precise estimates of age (e.g., Adams 1942; Meyer 1960; Johnson 1971; Oele et al. 2015). In these cases, other calcified structures (i.e., bones) such as cleithra and dentaries may be used to provide age estimates and back-calculate growth. In this chapter, we provide an overview of methods used to extract, prepare, and view cleithra, dentaries, and other bones when estimating age and growth.
The cleithrum (singular; cleithra—plural) is a paired bone in a fish’s pectoral girdle and is located directly posterior to the operculum (Casselman 1979). Numerous studies have evaluated age estimates from cleithra for a variety of fishes (e.g., White Sucker: MacCrimmon 1979; Razorback Sucker: McCarthy and Minckley 1987; Lake Trout: Sharp and Bernard 1988; Arctic Char: Baker and Timmons 1991); most of these studies concluded that other calcified structures provided more precise age estimates. However, for relatively long-lived esocid species (e.g., Muskellunge, Northern Pike), cleithra can accurately reflect age and growth information (Casselman 1979, 1990; Laine et al. 1991). For example, cleithra have been validated for Northern Pike up to age 11 (Babaluk and Craig 1990; Laine et al. 1991), yet their validity for age and growth estimation of Muskellunge has been assumed based on the close relationship between the two species (Robinson 2005). Numerous studies have demonstrated limitations of using fin rays and scales to estimate age of Muskellunge and Northern Pike (Johnson 1971; Casselman 1983; Fitzgerald et al. 1997). Despite their widespread use for age and growth estimation in other fishes, otoliths have been used infrequently for estimating age of esocids (Maceina et al. 2007; Rydell et al. 2008). Only recently have studies compared precision of age estimates derived from otoliths and cleithra for Northern Pike (Faust et al. 2013; Oele et al. 2015; Blackwell et al. 2016). Although age estimates were obtained from the two structures, cleithra were recommended due to a relative ease of interpretation and lack of necessary specialized laboratory equipment (Faust et al. 2013; Oele et al. 2015). However, Blackwell et al. (2016) recommended the use of otoliths for estimating age of Northern Pike because otoliths had higher precision relative to the other structures evaluated. Furthermore, cleithra may not be the best structure for all scenarios. For instance, if fish cannot be sacrificed, other structures (e.g., fin rays) may be necessary for age and growth estimation (Johnson 1971; Brenden et al. 2006).