Neotropical Ichthyology, 4(4):419-426, 2006 Copyright © 2006 Sociedade Brasileira de Ictiologia Diel feeding pattern and diet of rough scad Trachurus lathami Nichols, 1920 (Carangidae) from the Southwestern Atlantic Maria Raquel de Carvalho and Lucy Satiko Hashimoto Soares Diel changes in feeding activity and dietary composition of the rough scad Trachurus lathami were investigated through the analysis of stomach contents of 307 fish sampled over a 24-h period on the continental shelf off Ubatuba (23o 35´S 45oW). Stomach contents were analyzed by frequency of occurrence (O%), percent number (N%), percent mass (M%), and feeding index (FI% = O% * M%). Rough scad fed on mollusks (Gastropoda, Crepidula sp.), crustacean (Ostracoda, Copepoda, deca- pod larvae), chaetognat and teleostean fish. The main items were calanoid copepods (Eucalanus sp. and Centropages sp.). According to the analysis of the stomach fullness and prey digestion, T. lathami is both a diurnal and nocturnal feeder, showing some seasonal variation in feeding time. According to the Chronobiology concept, it was raised the hypothesis of circadian rhythm in feeding of this fish, probably synchronized by light/dark cycle. O estudo da dieta e do padrão diário e sazonal de atividade alimentar do chicharro Trachurus lathami foi realizado através de análises dos conteúdos estomacais de 307 peixes amostrados em estações fixas de coleta de 24 horas na plataforma continental ao largo de Ubatuba (23o 35´S 45oW). Os conteúdos estomacais foram analisados através da freqüência numérica (N%), massa porcentual (M%) e freqüência de ocorrência (O%) dos itens alimentares, e índice alimentar (O% * M%). A espécie caracterizou- se por ingerir principalmente copépodes calanóides (ex. Eucalanus sp. e Centropages sp.), além de outros crustáceos (Ostracoda, larva de decápodes), moluscos (Gastropoda: Crepidula sp.), quetognatos e peixes teleósteos. De acordo com o grau de repleção estomacal e grau de digestão das presas, T. lathami ingeriu alimento tanto na fase clara quanto na fase escura do dia, apresentando variação sazonal no horário de tomada de alimento. De acordo com os conceitos da Cronobiologia foi levantada a hipótese de ritmo circadiano na atividade alimentar, provavelmente sincronizado pelo ciclo claro/escuro. Key words: Food Habits, Feeding Ecology, Stomach Contents, Rhythms, Southeast Brazil. Introduction sic tools to understand the autoecology of fish species. And studies on diet composition may contribute to clarify prey- The critical and limiting resources for all animals are food predator relationships, and to elaborate trophic models for and time. Food provides energy and nutrients for reproduc- the assessment of stocks (Christensen & Pauly, 1992). tion, and to develop, maintain, and protect the somatic body. Most species of Trachurus are widely distributed in both Time is necessary for foraging, as well as for other activities, temperate and tropical coastal waters. Fifteen species are rec- such as resting and reproduction (Wootton, 1990). Accord- ognized (Suda et al., 1995). Only Trachurus lathami Nichols ing to chronobiologists, the majority of organisms present a 1920 occurs in the south-western Atlantic from the Gulf of circadian rhythm in their activities and this organization is the Maine (United States of America) down to the north of Ar- result of an evolutionary process that expresses a gentina. It is a demersal-pelagic species, with maximum size synchronicity among geophysical, environmental and bio- about 40 cm of length and 0.5 kg of mass (Menezes & Figuei- logical events (Marques & Menna-Barreto, 2003). Among redo, 1980), occurring in waters from 50 to 100m in depth, at marine, estuarine, and freshwater fishes, there are several temperatures between 15o and 17o C and salinity between 35.5 records of feeding activity with circadian rhythm (see Neilson and 35.8 (Saccardo & Katsuragawa, 1995; Mello et al., 1992). & Perry, 1990; Boujard & Leatherland, 1992, Sánchez-Vázquez Trachurus lathami is an abundant species on the south- et al., 1997, Gerkema et al., 2000). eastern Brazilian coast and represents a potential fishing re- Studies on diel feeding in the natural environment are ba- source (Saccardo & Katsuragawa, 1995). Instituto Oceanográfico da Universidade de São Paulo, Caixa Postal 9075, 01065-970 São Paulo, SP, Brazil. e-mail: [email protected] 419 420 Diel feeding pattern and diet of rough scad Trachurus lathami Considering that there are few studies on diet composition 23o 20’S of T. lathami (Pedreira, 1997; Crispino, 1995) and there are no studies about diel feeding of this species, we proposed to iden- Couves tify its pattern of daily feeding activity, and to describe the Is land variation of its diet composition during the course of the day. Ubatuba Study area. The study site is located on the continental shelf 23o 30’ S of the coastal system off Ubatuba (23°35’S, 45°00’W), Brazil, Anchieta southwestern Atlantic (Fig. 1). Is land Different water masses are present in this area during sum- mer and winter. During summer, there is a two-layer vertical Caraguatatuba Winter/88 stratification due to the seasonal thermocline: the upper layer 50 m consists of warmer and less saline Coastal Water – CW (T=22- o 23o 40’ S 24 C; S=35-35.4) and the lower of colder South Atlantic Cen- Atlantic Ocean tral Water – SACW (T=14-15oC; S=35.6-35.8). During the win- ter, only Coastal Water is present on the inner shelf (Castro & Miranda, 1998). Vitória Island São Sebastião Materials and Methods Búzios Island São 23o 50’ S Sampling. Rough scad were sampled during the periods 22- Sebastião Summer/88 24 July 1988 and 4-6 December 1988 on the continental shelf Is land off Ubatuba, São Paulo State, Brazil (Fig. 1). On each cruise, samples were collected in two consecutive 24-hour periods 45o 30’ W 45o 20’ W 45o 10’ W 45o 00’ W 44o 50’ W at 3-hour intervals, through 30 min trawls. From the total catch, a sample of at least 30 specimens Fig. 1. Sampling area on the southeastern Brazilian shelf and were randomly separated for biological analysis, size consid- the trawl stations location. ered suitable for this type of study (eg. Livingston, 1982); all available individuals were collected from the small samples. A de Zoologia da Universidade de São Paulo (MZUSP 65886, total of 307 stomachs were considered in this study (Table 1). MZUSP 65888, MZUSP 25887). The specimens were frozen, and the total length and total mass of each individual were measured in the laboratory. The Laboratory methods. A fullness level was assigned for each stomachs were removed and preserved in 10% buffered for- stomach: empty, half full and full (Hyslop, 1980). The stom- malin solution. ach content was sorted taxonomically and the degree of di- Regional samples of this species are deposited in Museu gestion (1-fresh prey; 2- partially digested prey; 3- digested Table 1. Sampling information for Trachurus lathami from Brazilian shelf off Ubatuba. Winter time (h) phase stomach size range (mm) <115mm >115mm mean mass (g) (n) (n) (n) 22/07/88 15:13 to 15:43 afternoon 17 104-128 8 9 16.69 22/07/88 18:17 to 22:15 night 37 110-157 3 34 22.31 23/07/88 00:10 to 00:40 night 6 111-136 1 5 16.74 23/07/88 10:46 to 11:16 morning 26 104-153 5 21 17.99 23/07/88 15:23 to 15:53 afternoon 2 112-114 2 0 14.25 Total 88 104-157 19 69 17.60 Summer time (h) phase stomach size range (mm) <115mm >115mm mean mass (g) (n) (n) (n) 12/4/1988 14:06 to 17:37 afternoon 36 53-92 36 0 3.11 12/4/1988 23:04 to 23:34 night 1 149 0 1 31.80 12/5/1988 02:43 to 03:13 night 5 65-155 1 4 22.12 12/5/1988 05:11 to 05:41 dawn 29 79-175 4 25 30.07 12/5/1988 08:55 to 11:40 morning 35 56-154 33 2 4.93 12/5/1988 15:05 to 17:39 afternoon 37 54-167 17 20 22.20 12/5/1988 20:01 to 20:31 night 10 56-168 3 7 32.68 12/6/1988 02:05 to 02:35 night 9 53-170 5 4 15.99 12/6/1988 05:13 to 05:43 dawn 28 55-170 15 13 19.56 12/6/1988 08:00 to 08:30 morning 29 48-97 29 0 3.38 Total 219 53-175 143 76 18.58 M. R. de Carvalho & L. S. H. Soares 421 prey) was assigned for individual items, according to Soares with temperatures between 21 and 23oC and salinity between & Apelbaum (1994). The state of digestion of the total stom- 35.3 and 35.9, and the other with temperatures between 15 ach content was assigned based on the proportion of prey in and 19oC and salinity between 35.5 and 36. The temperature a particular state in the content: fresh, more than 75% of the profiles are shown in Fig. 2. prey in a fresh state; partially digested, 25-75% of fresh con- tent and digested, less than 25% of fresh prey. Diel feeding activity. The stomach’s fullness levels and index of fullness showed the same diel pattern during the winter and Data analysis. Diel feeding activity was analyzed according summer (Figs. 3-4). Full stomachs occurred in the afternoon to data on stomach’s fullness levels (%), stomach index of and at night. Empty stomachs occurred only in the summer, in fullness (BM% = mass of the stomach content X mass of the the early morning and at dawn. Data on index of fullness re- fish-1 X 100), state of digestion of the stomach content (%), vealed a pattern of daytime feeding, attaining maximum values and number and frequency of fresh prey.