Rajaguru; Biology of Cynoglossus arel and C lids from Indian waters 



361 



Diet of fishes is related not only to their feeding 

 behavior, but also to their digestive morphology and 

 mouth structure (Stickney et al. 1974). In C. arel and 

 C. lida, jaws are asymmetrical so that the mouth points 

 to the bottom when opened, aiding feeding upon ben- 

 thic prey. Flatfishes that feed on benthose usually have 

 asymmetrical jaws (Pearcy and Hancock 1978). Cyno- 

 glossus arel, C. lida, and other tonguefishes are, in 

 general, polychaete feeders. These fishes have small 

 stomachs (not highly demarcated) and long intestines, 

 and lack gillrakers and pyloric caecae. 



Although there were similarities in food items, im- 

 portance of prey species differed between adults and 

 juveniles. Juveniles of C. arel and C. lida, probably 

 owing to their very small mouths, fed predominantly 

 on smaller prey such as amphipods and copepods, and 

 ingested fewer types (only 10) of food items. Adults of 

 both species, in contrast, had eaten 24 and 29 types, 

 respectively, of relatively large-sized prey, primarily 

 polychaetes, prawns, crustacean fragments, and fish 

 remains. Mouth size severely limits the size of prey 

 which can be ingested (Stickney 1976). According to 

 Honda (1984), the extent of food demand and ability 

 for food acquisition increase with growth and devel- 

 opment of fish. Lande's (1976) findings on the dab 

 Limanda limanda revealed that larger fish consumed 

 large-sized prey compared with smaller fish. Pearcy 

 and Hancock (1978) studied feeding habits of Dover 

 sole Microstomus pacificus, rex sole Glyptocephalits 

 zachirus, slender sole Lyopsetta exilis, and Pacific 

 sanddab Citharichthys sordidus off Oregon, and con- 

 cluded that the number and size of prey taxa gener- 

 ally increased with size in these flatfishes, due to the 

 ability of larger fish to consume a larger range of prey 

 sizes than smaller fish. 



During the present investigation, fewer empty stom- 

 achs were noted in female than male (11.6% vs. 18.0%) 

 C. lida. A similar trend was observed by Langton 

 (1983) for yellow-tail flounder Limanda ferruginea off 

 the northeastern United States. In female and male 

 C. arel, the percentage occurrence of empty stomachs 

 was similar (7.7% vs. 8.0%). 



Sexual differences in food and feeding habits of flat- 

 fishes have not been reported. In this study, there was 

 some indication of differences in prey between males 

 and females. The primary food group (polychaetes) was 

 the same in both sexes of C. lida; however, polychaetes 

 were somewhat more important in females (IRI 65.9%) 

 than males (IRI 53.4%). Moreover, the breadth of the 

 diet was somewhat less in females which fed upon only 

 19 food types, in contrast to males in which 24 prey 

 types were consumed. 



The present analysis on feeding intensity reveals that 

 in males of C arel, the peak occurrence of empty 

 stomachs had a positive correlation with peak spawn- 



ing activity (in January). Spavniing fish contained 

 the least amounts of prey, or had empty stomachs. 

 This result is consistent with the findings of Rama- 

 nathan and Natarajan (1980) on Indian halibut Pset- 

 todes erumei and floimder Pseudorhombtis arsius, and 

 with those of Langton (1983) on yellowtail flounder 

 Limanda ferruginea. However, in female C. arel and 

 both sexes of C. lida, the occurrence of empty stomachs 

 had no obvious relationship with spawning activities. 

 Seshappa and Bhimachar (1955) also reported that in 

 Malabar sole C. semifasciatus, feeding intensity was 

 not interrupted by increased reproductive activity. 



Male and female C. arel showed an inverse relation- 

 ship between gastrosomatic/hepatosomatic indices and 

 breeding cycle, with the lowest values observed dur- 

 ing peak spawning (in January). This indicates that 

 gut/liver energy reserves may be used for gonadal 

 recrudescence. Such a correlation was observed by 

 Ramanathan (1977) for the Indian halibut Psettodes 

 erumei and flounder Pseudorhombus arsius. Wingfield 

 and Grimm (1977) found HI to be highest in the 

 prespawning season and lowest in the postspawning 

 period of the Irish Sea plaice Pleuronectes platessa. 

 However, C. lida did not show a relationship between 

 gastrosomatic/hepatosomatic indices and breeding 

 cycle. 



Although the primary diet of these two demersal flat- 

 fishes consisted of benthic prey such as polychaetes, 

 prawns, echinoderms, and molluscs, it was surprising 

 to find that pelagic amphipods (<59.2% IRI) and 

 copepods (<44.7% IRI) were also relatively important 

 in their diets, especially in juveniles. Cynoglossus arel 

 and C. lida are demersal flatfishes that have never been 

 caught in the pelagic waters off Porto Novo, either 

 during day or night. These tonguefishes are not known 

 to undergo vertical feeding migrations. Based on the 

 present study, it is speculated that these tonguefishes 

 ingested pelagic prey such as hyperiid amphipods and 

 copepods when these prey organisms approached or 

 contacted the bottom during vertical migrations 

 through the water column. Hyperiid amphipods have 

 been reported to undertake extensive vertical migra- 

 tions (Bowman et al. 1982, Roe et al. 1984, Clark et 

 al. 1989). Isaacs and Schwartzlose (1965) and Pereyra 

 et al. (1969) have reported that in the eastern North 

 Pacific Ocean, demersal fishes feed on pelagic prey, 

 when such prey approach the bottom along the edge 

 of the continental shelf. 



Polychaetes, prawns, amphipods, copepods, crusta- 

 ceans, and fishes were important prey for both Cyno- 

 glossus arel and C. lida. These tonguefishes shared 

 25 different food items as prey (out of 30 food types 

 in C. arel, and out of 26 in C. lida). High overlap in 

 diet may reflect abundant prey resources, reducing 

 competition. Lande (1976) observed such a high prey 



