Abstract: Background and Objective: The relationships among the morphometric measurements of fish provide valuable information about the speciation phenomena induced by abiotic and biotic factors. Considering the importance of Mugil curema as a fishery resource and the scarcity of studies about Pratiqueira at the marajoara region, four experimental trawls were performed on Pesqueiro Beach in June 2008 aiming to determine the biometric relationships of Pratiqueira. Materials and Methods: A trawl net was used with the following specifications: length 48.12 m, height 2.37 m, mesh 25 mm, distance between opposite nodes 50 mm, distance between buoys 94 cm and distance between the sinkers 94 cm. Results: A total of seven specimens of Mugil curema were captured. The linear regression analysis revealed that both the height-total length (r2 = 0.8109, p<0.05) and fork length-total length (r2 = 0.7886, p<0.05) relationships showed negative allometry, with values b = 0.33 and 0.70, respectively. Conclusion: The present study revealed that the species in this study developed some structure in its body to develop a determined function.
INTRODUCTION
The Marajó archipelago has strategic and privileged position, being the largest fluvial-marine archipelago of the world. It is located near the equator, which runs almost parallel to the north. Its geographic coordinates are between the parallel 0°10'S-1°48'S and longitudes 48°22'W-50°49'W. In its northwestern portion, receives fresh and muddy water from the mouth of the Amazon River while receives northward the marine waters of the Atlantic Ocean. It receives northeast fresh and muddy water from Marajó Bay and receives southern fresh and muddy water from Pará River1,2.
The fishing is one of the most important and traditional activities of the island, given its importance in the food requirements of populations and in the economic activity that represents3. The mullets are a group of fishes of economic importance4 in the Marajó Island.
Pratiqueira or mullet, Mugil curema lives in tropical and subtropical waters of the Atlantic and Pacific Oceans5 with few populations in African waters6,7 and occur throughout the Brazilian coast8. It is a pelagic species that lives in the water column or in the surface, being that the juveniles occur in the estuary9 and even in freshwater10, inhabit quiet, sheltered and food-rich environment, until their gonads begin maturing. Their spawning occurs in offshore, but an estuarine phase is mandatory for juveniles, which follows the reproductive migration period to the sea11.
In fish, size is more biologically relevant than age, mainly because several ecological and physiological factors are more size-dependent than age-dependent. Consequently, variability in size has important implications for diverse aspects of fisheries science12. The knowledge of growth parameters such as length is pivotal for studies on population dynamics13.
The relationships among the morphometric measurements of fish provide valuable information about the speciation phenomena induced by abiotic and biotic factors14. Moreover, it has been useful for separating species, populations and races, being of vital importance to identify the study population in order to understand its dynamics15.
The relationship between the same unit of measure is isometric when the regression coefficient is equal to 1.0. When the values are statistically higher or lower than 1.0, indicating an allometric relationship, i.e., the distinct growth of a feature in relation to another16. This coefficient indicates any changes in shape over ontogeny17.
The correlation or degree of association among the characteristics is a very important parameter in the evaluation of a biometric feature18. The usage of regression analysis to explain the biometric relationships are found to be most suitable19 being necessary for the description of species20.
Considering the importance of Mugil curema as a fishery resource and due to little information about the biology of this species in the marajoara region, this survey intended to determine the biometric relationships of Pratiqueira caught by trawl net on Pesqueiro beach.
MATERIALS AND METHODS
Study area: The Pesqueiro beach was located 8 km east far from the town of Soure, situated in the Marine Extractive Reserve of Soure. This area was dominated by mangroves and sand dunes that spread throughout most of its length. During winter, the estuarine volume surpasses the amount of sea water leaving little saline the beach. In the summer the force changes and the beach becomes salted due to influence of Atlantic Ocean (Fig. 1).
Four experimental trawls with a total time of 2 h 33 min were carried out on Pesqueiro beach on Wednesday, 11 June 2008. Specification of trawls as well as their geographic coordinates were specified in Table 1.
| Fig. 1: | Study area |
| Source: Google Earth (2008) | |
| Table 1: | Specification of trawls and their geographic coordinates |
Experimental design: It was used in each trawl as fishing gear a trawl net with the following specifications: length 48.12 m, height 2.37 m, mesh 25 mm, distance between opposite nodes 50 mm, distance between buoys 94 cm and distance between sinkers 94 cm. The trawls were made at ebb tide, being the last performed at flood tide.
In the biometry were collected height measurements (H) that included the dorsal and ventral contour of body on the direction of the pectoral fin, total length (TL), which runs from snout to the caudal tip and fork length (FL) comprising the snout tip and the caudal fork. The instrument used for these measures was a 5 m measuring tape.
Data analysis: The biometric data underwent to descriptive statistic and to a simple linear regression analysis with significance level of 5%, according to the following equations:
| (1) |
and
| (2) |
where, H is body height (cm), FL is fork length (cm), TL is total length (cm), a is regression constant and b is regression coefficient.
Statistical analysis was performed using the programs BioEstat 5.021 and Microsoft Excel for Windows, version 2007.
RESULTS AND DISCUSSION
Overall seven fishes were caught in trawls, being two on the first, one on the second and four on the third trawl. The largest individual caught showed 29 cm TL while the smallest specimen had 25 cm total length (TL). Data in Table 2 showed the statistical values of the biometric parameters in this work.
The maximum total length found in this study agreed with the value found by Rocha et al.22. The authors analyzed the growth frequency in length of Mugil curema and found that the largest individual presented 28 cm TL.
It was recorded in this survey the value of mean total length 26.73 cm, which did not coincide with the findings of Szpilman8.
| Table 2: | Descriptive statistic of biometric parameters |
| TL: Total length and FL: Fork length | |
The author report that the average body size of this species is 30 cm. On the other hand, Oliveira et al.23 found the value of mean total length 24.9 cm in coastal waters of Rio Grande do Norte State, Brazil. It is important to highlight that the value found in the present survey referred to populations of estuarine environment, which was consistent with the use of the estuary both by adults and juveniles in the fattening stage, therefore, smaller sizes than the general average of the species. Thereby, Pesqueiro beach offers adequate conditions for the development and survival of juveniles.
The most likely fact that the average body size shown here be lower than that recorded in the literature may also be related to a beginning of overexploitation of this species in the region or other environmental factors, which would need a management plan for this commercial species. In general, any of the assumptions made require more detailed studies.
The linear regression analysis revealed significant differences between the parameters (p = 0.0064) showing that the height-total length relationship presented negative allometry, with value b = 0.33. In this study, the value of r2 explained 81.09% of the height increased with the variation in the TL (Fig. 2).
The fork length-total length relationship showed statistically significant difference (p = 0.0082), showing negative allometric growth, with value b = 0.70, being the value of r2 explaining 78.86% the increase in the FL with the variation of TL (Fig. 3).
An accurate interpretation of the allometry coefficients obtained allowed to say that for every 1% increase in total length, there was an increase of 0.3291% in height and increase of 0.7081% in the fork length.
It was found that both biometric relationships showed negative allometry. Indeed, this result revealed that the both height and fork length grew more slowly than the total length. This fact was confirmed by Fonteles-Filho24, which proposed that both negative and positive allometry could mean the highlight of a body part to perform a determined function.
| Fig. 2: | Height-total length relationship of Mugil curema caught on Pesqueiro beach |
| Fig. 3: | Fork length-total length relationship of Mugil curema caught on Pesqueiro beach |
The value of the allometry coefficient found in the fork length-total length relationship in this survey was in agreement with Araujo and Silva25. The authors studied the fork-length length relationship of fish species captured in the Vaza Barris River estuary, Sergipe State, Brazil and reported negative allometric growth for Mugil curema (b = 0.77).
In contrast to the present study, Ibanez-Aguirre et al.15 identified the isometric growth on population of Mugil curema located in the Gulf of Mexico. This fact was due to the length and height parameters in fishes to be influenced by the reproductive period, food availability and set of abiotic factors of each environment, which may affect the estimated values of biometric relationships and consequently the change in regression coefficient.
Verreth26 declared that the allometric growth of fish accurately reflected the change in the functional requirement related to changes in environmental hydrodynamics. This implied the early development of head, eyes, brain, gill arches as well as the recruitment and growth of muscle fibers to food consumption. Nevertheless, in the present survey adult Pratiqueira showed a late growth. The most likely cause can be the local environmental conditions which not require major functionality of the morphometric structures, providing thereby a smaller gain in height and fork length.
CONCLUSION
The present study reported that both the height-total length and fork length-total length relationship showed negative allometric growth for individuals of Mugil curema, revealed that the species in this study developed some structure in its body to develop a determined function.
SIGNIFICANCE STATEMENT
The present study reported for the first time the biometric relationships about specimens of Mugil curema on Pesqueiro Beach, Marajó Island. The importance of these findings is not restricted to knowledge of the biology of fishes, but has its practical and fundamental side to show the possibility of further studies in other areas of this region in order to determine parameters that allow an accurate study of the species.