Ecological separation by ecomorphology and swimming performance between two congeneric fish species

Ecomorphological relations of sympatric juveniles of Clupeiformes from a Brazilian sandy beach

ABSTRACT Surf zones are important for early life stages of several fish species for presenting characteristics such as high phytoplanktonic production, diverse food availability and shelter against predators. The action of waves in this environment provides nutrient cycling and increase the turbidity making surf zones ideal nursery environments for diverse species of fish, including clupeiforms. Clupeiform species have a great ecological and economic value for being abundant fish in tropical sandy beaches surf zones with significant fisheries importance. Studies about their feeding ecology and environment use are relevant, and one of the methods improving this knowledge is the application of ecomorphological analyses, which helps understanding species ecological interactions and their adaptations. In this context, the present study aimed to identify the ecomorphological relations and infer about the feeding ecology of eight sympatric clupeiform species in a Brazilian tropical sandy beach. Ten ecomorphological variables were analyzed of individuals belonging to the species Anchoa tricolor (Spix & Agassiz, 1829), Anchoa januaria (Steindachner, 1879), Anchovia clupeoides (Swainson, 1839), Anchoviella lepidentostole (Fowler, 1911), Lycengraulis grossidens (Spix & Agassiz, 1829), Chirocentrodon bleekerianus (Poey, 1867), Harengula clupeola (Cuvier, 1829) and Opisthonema oglinum (Lesueur, 1818), whose values were employed in a principal component analysis (PCA) with the two first axis explaining 58.92% of the total variance. A high morphological overlap between the species of Engraulidae was observed with the exception of A. clupeoides, which differed from the others for presenting higher values of the compression index and caudal peduncle compression index. The Clupeidae species differed from the other families due to higher values of relative height and relative head length which also showed differences between the species themselves, having H. clupeola presented the highest values of these variables. The representative of Pristigasteridae showed an intermediate overlap between the species of the other families because of its highly compressed body but with low scores of relative height, caudal peduncle relative length and mouth aspect ratio. The morphological differentiation between the families and even between species from the same family indicates niche divergences, showing that besides their phylogenetical proximity there are differences in their ecological interactions which possibly contribute to their coexistence.