Abstract
Abstract: Fish feeding habit associated to the morphology of their digestive tube can provide useful biological and ecological information. Between January and December 2012, we examined 16 fish species discarded by trawl in the Potiguar basin, northeastern Brazil, and classified them into four groups according to Alimentary Index - IAi. Our aims were to: (1) provide information on diet composition of one species represented by each group (Opisthonema oglinum, Conodon nobilis, Larimus breviceps and Sphoeroides testudineus), (2) examine the morphology of their digestive tube, and (3) associate ingested food items with the morphological features. Stomach contents were collected and classified according to IAi: main, accessory and secondary categories; fragments of esophagus, stomach, and small intestine were examined using paraffin section technique. Biometric data (total length-TL, standard length-SL and total weight-TW), stomach weight-SW, and gonadal weight-GW were recorded and applied in two indices: (1) the stomach Repletion Index - SRI (SRI = SW/TW × 100) and (2) the gonadosomatic index - GSI (GSI = GW/TW × 100) for the analyses of feeding and reproductive activities, respectively. The main food categories were (1) Teleostei for C. nobilis, (2) Crustacea for L. breviceps and O. oglinum, and (3) Mollusca for S. testudineus. The feeding activity was higher during the dry season, while the GSI was higher in the rainy season. The morphological analysis revealed a regular structure of the tissues analyzed. We highlight the presence of tubular gastric glands and strong muscular walls in the stomach (O. oglinum; L. breviceps); well-developed pyloric caecum in the intestine (O. oglinum; C. nobilis; L. breviceps); and presence of pseudo-stomach (S. testudineus). Our study confirms that the digestive tube of the examined species has morphological adequacy for carnivorous feeding habit, providing useful information on tissue structures associated to diet composition.
Highlights
The coast in Rio Grande do Norte State, Brazil, stretches over approximately 400 km, and is characterized by significant fishing activity with 76.5% represented by artisanal fisheries (Ibama 2010)
We analyzed the diet of 16 species discarded by trawl, which were classified into four groups, according to IAi: (I) Group represented by species with ‘Crustacea’ as the main food category, ‘Sediment’ as secondary or accessory category: L. grossidens and O. oglinum; (II) Group represented by species with ‘Teleostei’ as the main food category: C. nobilis, B. bagre, B. marinus and G. micrura; (III) Group represented by species with ‘Crustacea’ as the main food category, ‘Teleostei’ as secondary or accessory category: P. virginicus, M. littoralis, S. brownii, D. guttata, L. breviceps, P. harroweri, A. luniscutis and P. corvinaeformis; and (IV) Group represented by species with ‘Mollusca’ as the main food category and ‘Echinodermata’ as accessory category: L. laevigatus and S. testudineus (Figure 2)
The relative abundance of Opisthonema oglinum, Conodon nobilis, Larimus breviceps and Sphoeroides testudineus was higher than the amount obtained by Feitosa et al (2013) in the same site and considering bycatch
Summary
The coast in Rio Grande do Norte State, Brazil, stretches over approximately 400 km, and is characterized by significant fishing activity with 76.5% represented by artisanal fisheries (Ibama 2010). Fish bycatch is often higher than capture of target species, especially in multi-target small-scale fisheries operating in the northwestern coast of Rio Grande do Norte (Silva-Júnior et al 2013). In this region, trawl fisheries conducted by small boats aim to capture shrimp; many fish are accidentally captured (Bomfim et al 2019). Concerns about bycatch of charismatic species such as dolphins and marine turtles have increased and quickly expanded to other species (e.g. juvenile fish discarded by bottom trawls) (Kennelly & Broadhurst 2002, Burgess et al 2018). Bycatch of juvenile animals influences their conservation and affect density and distribution of predators, resulting in a limited abundance and distribution (Block et al 2011, Stewart & Jones 2001)
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