1. Compression index |
CI = MBH/MBW |
Higher values indicate lateral compression of the fish, expected for fish that exploit habitats with slower water velocity (Gatz Jr., 1979; Watson & Balon, 1984). |
2. Depression index |
DI = BMH/MBH |
Lower values are associated with fish that exploit habitats with rapid water flow. Depressed body helps remaining in the water column without swimming (Hora, 1922; Watson & Balon, 1984). |
3. Relative length of the caudal peduncle |
RLPd = CPdL/SL |
Long caudal peduncle is associated with fish living in places with rapid water flow, owing the need for propulsion at short distances (Watson & Balon, 1984; Oliveira et al., 2010). |
4. Relative height of the caudal peduncle |
RHPd = CPdH/MBH |
Lower values indicate greater maneuverability potential (Winemiller, 1991; Oliveira et al., 2010). |
5. Relative width of the caudal peduncle |
RWPd = CPdW/MBW |
Higher relative values indicate better continuous swimmers (Winemiller, 1991; Oliveira et al., 2010). |
6. Relative length of the head |
RLHd = HdL/SL |
Higher values are found in fish that feed on large prey (Gatz Jr., 1979; Watson & Balon, 1984). |
7. Relative height of the head |
RHHd = HdH/MBH |
Higher values are found in fish that feed on relatively large prey. (Oliveira et al., 2010). |
8. Relative width of the head |
RWHd = HdW/MBW |
Higher values are found in fish that feed on relatively large prey (Oliveira et al., 2010). |
9. Relative height of the mouth |
RHM = MH/MBH |
Higher values are found in fish that feed on relatively large prey (Gatz Jr., 1979; Watson & Balon, 1984). Lower values are associated with greater suction capacity (Norton & Brainerd, 1993). |
10. Relative width of the mouth |
RWM = MW/MBW |
Higher values are found in fish that feed on relatively large prey (Gatz Jr., 1979; Watson & Balon, 1984). Lower values are associated with greater suction capacity (Norton & Brainerd, 1993). |
11. Eye position |
EP = EH/HdH |
Index related to the foraging position in the water column. Higher values represent species with dorsal eyes and possibly benthic, while low values indicate necton fish with lateral eyes. (Gatz Jr., 1979; Watson & Balon, 1984; Freire & Agostinho, 2001). |
12. Relative area of the eye |
RAE = EA/(SL)2
|
Index related to food detection. It can indicate the preferential position of the species on the water column, since species that inhabit deeper areas have relatively smaller eyes (Gatz Jr., 1979; Wikramanayake, 1990). |
13. Protrusion index |
PI = LSO/LSC |
Higher values related to the ability to capture evasive and large prey (Hulsey & García de León, 2005; Cochran-Biederman & Winemiller, 2010). |
14. Relative area of the dorsal fin |
RAD = DA/(SL)2
|
Species with dorsal fins with larger relative areas have better capacity to stabilization and braking in acceleration (Breda et al., 2005). |
15. Relative area of the caudal fin |
RAC = CA/(SL)2
|
Caudal fins with larger relative areas are important for acceleration (Breda et al., 2005; Oliveira et al., 2010). |
16. Aspect ratio of the caudal fin |
ARC = (CH)2/CA |
Higher values indicate fish with caudal fins with tendency to bifurcation, and generally are good swimmers for continuous swimming. Species with low values have caudal fins with larger areas and exhibit excellent performance for acceleration. (Breda et al., 2005). |
17. Relative area of the anal fin |
RAA = AA/(SL)2
|
Larger relative area indicates higher maneuverability capacity and movement stabilization (Breda et al., 2005). |
18. Aspect ratio of the anal fin |
ARA = (AL)2/AA |
Anal fins with larger aspect ratio indicate a higher capacity to make rapid progression and regression movements (Breda et al., 2005). |
19. Relative area of the pectoral fin |
RAPt = PtA/(SL)2
|
Larger areas can be directly associated with braking and acceleration (Gatz Jr., 1979; Watson & Balon, 1984). For benthic fish inhabiting rapids stretches, some authors have noted that large pectoral fins can increase the contact area with the surface, where the fish leans on, promoting thus a greater attachment to the substrate (Casatti & Castro, 1998; Kerfoot Jr. & Schaefer, 2006). |
20. Aspect ratio of the pectoral fin |
ARPt = (PtL)2/PtA |
Higher values represent long and narrow fins. The highest values are associated with increased swimming speed (Breda et al., 2005). For benthic fish inhabiting rapids, longer pectoral fins may favor the maintenance of the position amidst a strong current flow (Casatti & Castro, 1998). |
21. Relative area of the pelvic fin |
RAPv = PvA/(SL)2
|
Larger areas indicate benthic fish. Larger pelvic fin can increase the contact area with the surface where the fish leans on, promoting thus a greater attachment to the substrate (Casatti & Castro, 1998; Kerfoot Jr. & Schaefer, 2006), while smaller relative areas indicate pelagic fish (Breda et
al, 2005). |
22. Aspect ratio of the pelvic fin |
ARPv = (PvL)2/PvA |
High values denote long fins and are associated with braking (Gatz Jr., 1979). For benthic fish inhabiting rapids, longer pelvic fins may favor the maintenance of the position amidst a strong current flow (Casatti & Castro, 1998). |