Trophic niches and diet shifts of juvenile mullet species coexisting in marine and estuarine habitats

Food partitioning among coexisting species is often considered advantageous to minimize niche overlap and avoid inter-specific competition. Congeneric fish species such as the mullets Mugil curema and Mugil liza, which co-occur across marine and estuarine habitats, are good models to evaluate resource use and niche overlap or partitioning. We used stomach contents (SCA) and stable isotope analysis (SIA) to assess potential trophic shifts and changes in niche overlap associated with the mullets transitioning from marine to estuarine habitats. SIA included different fractions of organic matter in suspension and in the sediment to estimate the contribution of micro, nano and pico-organisms to the mullets’ diets. We hypothesized higher resource partitioning in the less resource-diverse system (marine surf-zone) than in the more diverse one (estuary). SCA showed diet differences between M. curema and M. liza according to the habitat. They showed distinct diets in the marine area (P < 0.001), but similar diets in the estuary (P = 0.226). A lower niche breadth was observed for both species in the marine area (M. curema = 0.03, M. liza = 0.06) compared with the estuary (M. curema = 0.14, M. liza = 0.16). Isotopic niches of both species were higher in the estuary (64.7%) compared with the marine area (0.7%). These findings corroborated our hypothesis of higher food partitioning in the marine surf-zone. We also demonstrated using SIA the shift from planktonic to benthic feeding following the recruitment of the mullets from the surf-zone into the estuary.

The influence of size on the trophic interactions between juveniles of two syntopic Trachinotus species

Syntopic species with similar anatomic configuration may face strong competition for trophic resources, thus relying on developed mechanisms to ensure coexistence. The present study investigated the influence of body size on trophic interactions between juveniles of two closely related fish species at three sandy beaches in south-eastern Brazil. A total of 150 fish were sampled, where 103 were identified as Trachinotus carolinus (mean ± SE: weight = 9 g ± 1.13) and 47 as Trachinotus goodei (weight = 46.7 g ± 3.34). A significant size-difference between juvenile Trachinotus was detected by a null-model analysis (P = 0.04), with T. carolinus (TL = 79.6 mm ± 2.4) presenting a smaller body size than T. goodei (TL = 147.7 mm ± 4.2). The main prey items consumed by T. carolinus were Perna perna (IAi = 0.76) and Emerita brasiliensis (IAi = 0.18), whereas the latter was the major T. goodei dietary prey (IAi = 0.71). Both prey were correlated with larger-sized juveniles of each pompano species, whereas smaller fish shared non-preferred trophic items. Such opportunistic behaviour of smaller juveniles may account for the dietary overlap detected between the Trachinotus species (P = 0.09). Size-related dietary partitioning was observed for the largest T. goodei juveniles, which displayed only a slight overlap with T. carolinus, and between juveniles belonging to the small and medium size groups of each pompano species. Therefore, food partitioning related to pompano body size seems to be especially important for the smallest juveniles, as they present the highest vacuity (particularly T. carolinus) in the sampled beaches, suggesting that these individuals are under intra- and interspecific competitive pressure, which may affect local coexistence.

Diet and food partitioning between juvenile of Epinephelus coioides (Perciformes: Epinephelidae) and other co-existing juvenile fishes in shallow waters of Thailand and Malaysia

This work examined diet composition of the juvenile orange-spotted grouper, Epinephelus coioides, and its trophic association with other juvenile fish species in tropical estuarine habitats during recruitment. From December 2015 to March 2016, juveniles were collected, their stomachs excised, preserved and analyzed. Small shrimps and amphipods, especially Grandidierella sp. and Elasmopus sp., were the most common food resources sharing among the most species. Epinephelus coioides predominantly ingested small shrimp, Grandidierella sp., Elasmopus sp. and fish larvae and had the greatest trophic overlap with Palatrus scapulopunctatus. Fish size, location and month significantly affected fullness indices and food items diversity in E. coioides. It is clear that the larger the size of E. coioides and its mouth opening, the larger the size of items ingested. This study confirms the ontogenetic dietary shift of juvenile E. coioides during recruitment season by starting as amphipod and small shrimp feeder and shifting to shrimp and fish larvae predator as they grow. This finding is fundamental to understanding how juvenile E. coioides cope with different conditions and its association with other co-existing species during the recruitment period.

FOOD PARTITIONING AMONG FISHES IN PAHANG RIVER-ESTUARY, MALAYSIA

A study was conducted on the food resource partitioning among fish species in Pahang River-estuary from 2010-2013 during pre-monsoon and post-monsoon period. The area was divided in three strata (upstream, downstream and middle zone), based on environmental features. Stomach contents of all species present were analyzed. From 138 of total stomach analyzed, 24 of them were empty and 114 were with food. From the analysis of prey in the stomachs, various kinds of food items consumed by the different size of fishes included phytoplankton, zooplankton, unidentified materials, fish, fish parts, shrimp, shrimp parts, crab, crab parts, plant parts, mollusk and detritus. Detritus consisted of all types of biogenic materials in various stages of microbial decomposition. Different fishes consume different types of food and feeding habit of fishes varies from season to season. From the percentage of number and occurrence of food resources, zooplankton are important in their own right as a major component of fish diets and are especially important to small and young individuals, even for the detrivore. Nevertheless, it represents an important trophic resource for fish food web of Pahang River-estuary.

Habitat use and food partitioning of the fishes in a coastal stream of Atlantic Forest, Brazil

We analysed the fish assemblage in the "Mergulhiio" stream (soulhem Brazil) with underwater observations for habitat use, considering water depth, current velocity, bottom type, shadow froID vegetation cover, distance of stream-edge, and vertical position. Stomach contents or foregut content samples of the most abundant species were collected from 26 species (lO families). The fish assemblage occupied the bottom stream. The similarity analysis of spalía! occupation of species grouped four habitat use guilds: A) "Iambaris" (Aslyanax sp. and Deutetodon langei), Characidium spp. (C. lane; and C. plerosliclum) and Rineloricaria kronei used the bottom in deep sites and waters with middle current; B) Pimelodella pappenheimi and Corydoras barbalus used the bottom in siles with JOwer cUI'l"ént; C) Mimagoniates microlepis used the surface of the water column; and D) Phalloceros caudimacullUus used shallow sítes and waters without current. Species with few records were analysed descriptively. Diet similarity suggested seven trophic guilds: Microglanis sp. and PiTMIodella pappenheimi: omnivorouslca:mivorous gui14; Corydoras barbatus: omnivorous/insectivorous guild; Characidium [ane;: aquatic insectivorous guild, Ilillinly aquatic insects; Mimagoniates microlepis: terrestriál insectivorous guild, mainly te.rrestrial insects; Deuterodon [angei and ASlyanax sp.: omnivorous/herbivorous guild; Rineloricaria kronei, Kronichth.yssubteres, Schizolecis guntheri. Hisonotus leucofrenatus and Pseudotothyris obtusa: herbivÓfous guild; and PhaUoceros caudimaculatus: a!givorous guild. When the guilds were similar, the species were geÍletalists in diet and in habitat use.