Diet and food preference of Caprodon longimanus were studied at Alejandro Selkirk Island, Chile. The fishes (N=55) were collected in November and December 1996 using long line and the sizes ranged from 176-286 mm in SL. This grouper is a pelagic opportunistic zooplanktivorous predator. Thalia sp. (Tunicata:Salpida) was the most frequent and abundant prey accounting for 93.3% occurrence based on 1655 individuals. A total of 17 genera of crustaceans as well as pteropods, chaetognaths and polychaete worms were found in the stomach contents. A total of 14.3% of all stomachs were empty.
Key words ]]>
Caprodon longimanus, Serranidae, stomach content analysis, Alejandro Selkirk Island, Eastern South Pacific, Chile.Groupers are carnivorous fishes that live near the bottom in littoral and sublittoral zones of tropical and subtropical seas. Most species occur on coral reefs, but some live in estuaries and are near or at the top trophic levels of the food chains. This group includes over 400 species within five subfamilies and most of them are of considerable economic value (Shpigel and Fishelson 1989, Heemstra and Randall 1993).
These fishes play an important role in coastal marine ecosystems where they are active predators of a number of organisms. Most groupers feed mainly on a variety of fishes, large crustaceans and cephalopods (Randall and Brock 1960, Randall 1967, Harmelin-Vivien and Bouchon 1976, Nagelkerken 1979, Diamant and Shpigel 1985, Parrish 1987, Shpigel and Fishelson 1989, Bullock and Smith 1991). Some species may even occasionally prey on juvenile turtles (Witzell 1981).
A few species, however, stand apart from this pattern eating small prey and showing specific adaptations for this feeding mode. They have long and numerous gillrakers that allow them to filter planktonic organisms (Parrish 1987, Bullock and Smith 1991, Heemstra and Randall 1993).
The genus Caprodon is a serranid that belongs to the subfamily Anthiinae and is composed by three species (Kharin and Dudarev 1983). Although there is abundant information in the literature regarding feeding habits of serranid species, groupers, sandbasses, etc., there is almost no information for any species of Caprodon.
The species C. longimanus (Günther, 1859) has an usual and interesting distribution, ranging from the Indopacific (Kharin and Dudarev 1983) to the southeastern Pacific islands (Sepúlveda and Pequeño 1985, Rojas and Pequeño 1997 in prep.), at depths from 3 to 200 m. The purpose of the present study is to provide the first information on the diet of C. longimanus at Alejandro Selkirk Island, Juan Fernández Archipelago, Chile.
Materials and Methods
Fifty-five specimens of C. longimanus were collected on November 21 and December 4, 1996 at Alejandro Selkirk (33°46’S, 80°46’W), the westernmost island of the Juan Fernández Archipelago. The fishes were caught by artisanal fishermen using long-lines. Their weights (± 0.5 g) and standard lengths (SL, ± 0.5 cm), were recorded and the stomachs were removed and preserved in 10% formaldehyde. The specimens were deposited in the Division of Marine Fishes, Institute of Zoology of University Austral of Chile (IZUA-PM 2016-2020). ]]>
In the laboratory, the stomachs were opened and the contents analyzed. The prey items were identified to the lowest taxonomic level following Palma (1985) and Palma and Kaiser (1993). Due to the nature of the food, the digestion rate, ineffective preservation, an important fraction of the samples contained material unidentifiable that was classified as "unidentified prey".The number of empty stomachs was also recorded.The numeric frequency and the frequency of occurrence were calculated according to Hyslop (1980) and Starck and Schroeder (1970) respectively. The most important prey items were determined according to index of dietary importance (DI) (Hureau 1969). The biomass of prey items could not be determined due to the high degree of digestion and the soft and delicate nature of the dominant prey items. Diversity, evenness, and dominance of prey were calculated using the computer package ACOM (Navarro 1984).
Results
Caprodon longimanus has a long oblique mouth, with the upper jaw extending past the lower jaw when closed. The jaw has two rows of villiforms teeth, with two small canines at the end of each row. The premaxilla has two rows of small conical teeth. Band broadest anterior end of jaws near symphysial diastem. A rhombus-shaped patch of about two rows are found on the vomer and on a band of two rows on the palatines. The tongue is slender, without teeth. The stomach cavity is narrow, short, and not heavily muscled.
The numbers of individuals and frequency of occurrence in each food category found in the stomachs are shown in Table 1. Based on the presence of mature gonads, all individuals were considered to be adults. A total of 14.3% of all the stomachs were empty and they correspond to individuals captured deeper than 150 m in the water column. The food items consumed by C. longimanus included salps, radiolarians, siphonophores, polychaets, pteropods, chaetognaths, tunicates and crustaceans. Five orders (Amphipoda, Calanoida, Decapoda, Euphausiacea, and Ostracoda) with 17 genera of crustaceans were represented (Table 1).
| A | B | DI | A | B | ]]> DI|||||||
| Prey category | (N) | (%) | N | (%) | ]]> Prey category | (N) | (%) | N | (%) | ||
| PROTOZOA | ]]>]]> | ||||||||||
| Radiolaria | 20 | 1.0 | 2 | 6.77 | II | unidentified ]]> | 9 | 0.5 | 5 | 16.7 | III |
| CNIDARIA | ]]> | Amphipoda-Hyperiidea | 68 | 3.5 | II | ]]>||||||
| Siphonophorae | 10 | 0.5 | 5 | 16.7 | III | Scina sp. | ]]> 20.1 | 1 | 3.3 | III | |
| Muggiaea atlantica | 5 | ]]> 0.32 | 6.7 | III | Vibilia sp. | 14 | 0.7 | 9 | 30.0 | ]]> III||
| Abylopsis tetragona | 3 | 0.2 | 1 | 3.3 | III | ]]> Paraphronima sp.2 | 0.1 | 2 | 6.7 | III | |
| Chelophyes ]]> | 2 | 0.1 | 2 | 6.7 | III | Lestrigonus sp. | 1 | 0.05 | ]]> 13.3 | III | |
| ANNELIDA | ]]> | Hyperietta sp. | 3 | 0.1 | 3 | 10.0 | III | ||||
| 12 | 0.6 | 4 | 13.3 | III | Streetsia sp. | 2 | 0.1 | ]]> 13.3 | III | ||
| Larvae | 6 | 0.3 | 2 | 6.7 | ]]> IIIPlatyscelus sp. | 3 | 0.1 | 2 | 6.7 | III | |
| 6 | 0.3 | 2 | 6.7 | III | unidentified Hyperiidea | 41 | 2.1 | ]]> 1446.7 | II | ||
| MOLLUSCA | ]]> | Euphausiacea | 10 | 0.5 | 8 | 26.7 | III | ||||
| Pteropoda | ]]> 60.3 | 4 | 13.3 | III | Nematoscelis megalops | 1 | 0.05 | 1 | ]]> 3.3III | ||
| CHAETOGNATHA | ]]> Larvae of Euphausia sp. | 9 | 0.4 | 7 | 23.3 | III | |||||
| Sagitta ]]> | 11 | 0.5 | 2 | 6.7 | III | Decapoda | 5 | 0.2 | 3 | ]]> 10.0III | |
| ARTHROPODA | ]]> Larvae | 5 | 0.2 | 3 | 10.0 | III | |||||
| Ostracoda | 6 | ]]> 0.35 | 16.7 | III | TUNICATA | ]]> | |||||
| Copepoda-Calanoida | 85 | 4.3 | II | Salpida | 1655 | ]]> 84.728 | 93.7 | I | |||
| Calanus chilensis | 4 | 0.2 | ]]> 26.7 | III | Thalia sp. | 1655 | 84.7 | 28 | 93.7 | I | ]]>|
| Nannocalanus sp. | 1 | 0.05 | 1 | 3.3 | III | Doliolida | ]]> 50.2 | 3 | 10.0 | III | |
| Ctenocalanus sp. | 1 | ]]> 0.051 | 3.3 | III | Appendicularia | 6 | 0.3 | 2 | 6.7 | III | ]]>|
| Rhincalanus sp. | 15 | 0.8 | 8 | 26.7 | III | Oikopleura ]]> | 6 | 0.3 | 2 | 6.7 | III |
| Pleuromamma sp. | ]]> 221.1 | 13 | 43.3 | II | VERTEBRATA | ]]> | |||||
| Euchaeta sp. | 3 | 0.1 | 2 | 6.7 | III | ]]> Pisces10 | 0.5 | 8 | 26.7 | III | |
| Centropages sp. | ]]> 10.05 | 1 | 3.3 | III | Eggs | 9 | 0.4 | 7 | 23.3 | ]]> III||
| unidentified Calanoida | 38 | 1.9 | 14 | 46.7 | II | ]]> Larvae1 | 0.05 | 1 | 3.3 | III | |
| Copepoda-Cyclopoida | 23 | ]]> 1.2II | Unidentified prey | 30 | 1.5 | 30 | 85.7 | ]]> II||||
| Sapphirina sp. | 14 | 0.7 | 9 | 30.0 | III | ]]> Total1953 | |||||
| unidentified Cyclopoida | ]]> 90.5 | 5 | 16.7 | III | ]]> | ||||||
Thalia democratica (Van Soest 1973) (Tunicata: Thaliacea), was the main prey item (by number of individuals recorded 1655 and frequency of occurrence 93.3%). Calanoids copepods (mainly Pleuromamma sp. with 43.3% frequence of occurrence) were the second most important food item. Radiolaria, Copepoda Cyclopoida and Amphipoda Hyperiidea as a group were the third prey item. Pisces (eggs and larvae), pteropods, chaetognaths, euphausids, decapods, doliolids and appendicularians were found only occasionally in the stomach content. Fishes might be more important in the diet of C. longimanus than our data suggest. Their identification proved difficult because of the advanced state of digestion. The diversity, dominance and evenness indices of the items prey was 0.89, 0.82, and 0.18 respectively.
A high number of stomachs had unidentifiable remains (85.7%) that contained scales, crustaceans appendges, destroyed eggs and components digested beyond recognition.
Discussion
The serranid fishes show a correlation between gillraker configuration and feeding habits. Those taxa with fewer and shorter gillrakers are generally carnivores, whereas the opposite holds for planktivores (Parrish 1987, Bullock and Smith 1991, Heemstra and Randall 1993) (Table 2). The condition of more developed and abundant gillrakers is present in C. longimanus, which suggests planktivorous feeding habits. In fact, this species has more gillrakers than any other serranid in the southeastern Pacific off Chile (Rojas and Pequeño 1997b in prep.).
Number of gillrakers (N) and prey preferences of some other serranids fishes from tropical and subtropical oceans.
| Taxa | Gillrakers (N) | Prey | ]]> LocationReference | |
| Acanthistius brasilianus | 20-27 | Sh-F | Argentina | Goldstein ]]> |
| Anthias nicholsi | 39-44 | C-P | Florida | Bullock and Smith 1991 | ]]>
| Anthias squamipinnis | 31-36 | C | Red Sea | Shapiro and Genin 1993 | ]]>
| Anthias tenuis | 34-39 | C | Gulf of México | Bullock and Smith 1991 | ]]>
| Caprodon longimanus | 31-39 | A-C-S-L | Chile | Present study | Dicentrarchus labrax | 32-35 | C | France | Roblin and Brusle 1984 |
| 18-21 | Ca | Jamaica | Nagelkerken 1979 | |
| E. ]]> | 24-28 | Sh-F | Puerto Rico | Randall 1967 |
| E. ]]> | 24-27 | Sh-F | Bahamas | Thompson and Munro 1978 |
| E. itajara | ]]> 22-24Sh-F | Florida | Bullock and Smith 1991 | |
| Hemanthias peruanus | 31-34 | ]]> CPerú | Heemstra 1995 | |
| Hemanthias leptus | 35-40 | C-O | ]]> FloridaBullock and Smith 1991 | |
| Holanthias martinicensis | 34-41 | C-O, P | ]]> BermudaBullock and Smith 1991 | |
| Hypoplectrus unicolor | 17-20 | Sh-F | Florida | ]]> Bullock and Smith 1991|
| Paralabrax humeralis | 27-30 | F | Chile | Borquez ]]> et al. 1988 |
| Plectropomus leopardus | 21-26 | F | Australia | Kingsford 1992 | ]]>
| Serranus annularis | 15-18 | Sh-E | Bermuda | Robins and Starck 1961 |