NOTE Raymundo-Huizar et al.: Feeding habits of Cynoscion nannus 



457 



whereas towards the end of the year, penaeid shrimp 

 were eaten in higher proportions (W f = 50.6%). During 

 May, stomatopods and carideans were found with higher 

 biomass values than during the rest of the year lW^ 

 = 68.2% and 20%, respectively). Cephalopods were found 

 in most months with biomass values ranging from 4% 

 to 34% of consumed biomass. 



The mean value of diet diversity was 0.41 (±0.18 

 CI g5<7t ). Although the number of dietary categories for 

 C. nannus that were identified was high (29 prey types), 

 there were a few items with significant importance. 

 Monthly variations in Ba ranged from 0.1 to 0.8 (Fig. 

 3). During most of the period analyzed, Ba values were 

 not significantly different from each other as shown by 

 the lack of overlap between CI 95 ,-. The only exceptions 

 were January and April, when CI 95% was above the 

 mean Ba ±CI 95Q value, and October when Cl S59 was 

 below the mean Ba. 



Discussion 



Cynoscion nannus is a carnivorous fish that feeds on 

 at least 29 different prey types. Although cannibal- 

 istic behavior has been reported for several fish spe- 

 cies in a variety of habitats and life-history strategies 

 (Smith and Reay, 1991), C. nannus as a prey type was 



found in only 0.8% (two individuals >15.0 cm TL) of all 

 stomachs analyzed. According to the IRI values, crus- 

 taceans — specifically juvenile shrimp and stomatopods 

 of the genus Squilla — appear to be the most important 

 items in the diet. The type of substrate can influence 

 the feeding habits of these fish. For example, Minello 

 and Zimmerman (1984) observed that under experimen- 

 tal conditions, the feeding preferences of C. nebulosus 

 (16 cm^TL<;21 cm) for Farfantepenaeus aztecus varied 

 depending on the substrate. These authors suggested 

 that substrate characteristics determine the burrow- 

 ing capacity of F. aztecus and thus predator avoidance. 

 In the study area, juvenile shrimp and stomatopods 

 of the genus Squilla can be abundantly found in soft- 

 bottom habitats (Gonzalez-Sanson et al., 1997). Both 

 the cephalopod iLoliopsis diomedae) and the fish spe- 

 cies found in the stomach contents of C. nannus are 

 pelagic or demersal species, indicating that the feeding 

 activities of C. nannus are not exclusively limited to the 

 benthos, and that this species can forage throughout 

 the water column. Results in the present study provide 

 evidence that fish feeding at different water depths have 

 access to a broader variety of prey types. This has been 

 shown both for other Sciaenidae (Chao and Musik, 1977; 

 Campos and Corrales, 1986; Chao, 1995; Pelaez-Rodri- 

 guez, 1996; Cruz-Escalona, 1998), and other species of 

 demersal fish (Lucena et al., 2000). 



