The penaeid shrimp resources of the country which constitute the coastal shrimp fishery occupy different ecosystems such as estuaries, inshore and offshore waters having its own distribution patterns, sizes and breeding activities. This situation requires monitoring of the population characteristics of each species separately to keep track of effects of exploitation of the stocks. Knowledge of stock composition is the fundamental tool for effective management of mixed stock fisheries, absence of this can lead to over exploitation. However, very little work has been done in India to determine to what extent the prawn stocks vary especially for Penaeus species - which differ genetically along their spatial range of distribution. The green tiger shrimp Penaeus semisulcatus is one of the commercially important penaeid shrimps species in both capture and culture fisheries due to its large size and fast growth rate. But, despite its wide distribution and commercial importance, very little long-term research on its biology has been published. In India, the species is abundant along the east coast than the west (Kurian and Sebastian, 1976). In earlier years, more than half of the shrimp landings of Gulf of Mannar and Palk Bay were contributed by this species but declined in later years (Nandakumar, 1980; Manickam et al., 1989). The fishery (Manisseri, 1982, 1986), biology (Thomas, 1975, 1981) and growth (Thomas, 1977) of P. semisulcatus were studied in detail along the east coast. Juvenile fishery of the species was reported from Cochin backwaters (Rao and Kathirvel, 1972) and Ashtamudi Lake (Suseelan and Kathirvel, 1979). But the genetic structure of most economically important shrimp populations still remain unknown due to absence of gene frequency data. The stock studies of P. indicus (Paul, 2000) and P. monodon (Rebello, 2003; Rebello et al., 2013, 2015a, b, c) stands first in this regard to assess the stock structure of these commercially important marine prawns. Electrophoretic studies on planktonic juveniles and adults of P. indicus and P. monodon also have been done (Samuel, 1987).
 

Considering the importance of these studies, morphometric and electrophoretic investigations were carried out in commercially important P. semisulcatus. Investigation on one of the variable factors among the species in morphological characters related to size, shape or other commercial characters are quite limited except for correlating these variations to the tail weight of the species (Goswami et al., 1986; Lester, 1990; Lester and Pante, 1992; George, 1997; Paul, 2000; Rebello, 2003, Rebello et al., 2013, 2015a, b, c). The electrophoretic study of biochemical analysis of protein and enzymes - Aldehyde oxidase (AO), Aldolase (FBALD), Octanol dehydrogenase (ODH), and Esterase (EST) were done by Polyacrylamide Gel Electrophoresis (PAGE).
 

Population samples of Penaeus semisulcatus were randomly collected from selected landing centres such as Kochi and Calicut of west coast of Kerala. These samples captured by trawl net, purchased from landing centres were frozen and transported to the laboratory in wet ice and then stored at ^-20ºC until used for experiments. A total of 80 specimens of P. semisulcatus with a length of 115 -171 mm and weight of 11- 54 g were collected.
 

The thawed samples were weighed individually using the electronic weighing balance (in gram) and a set of 4 variables were measured (in mm) (Fig.1). The variables measured were the depth of the abdomen (SSD) at the mid-point of the sixth segment; depth of the abdomen (SAD) at the intersection of the second and third segments, partial carapace length (PCL) from the posterior margin of the orbit to the posterior edge of the carapace; width of the carapace (CW) at the point of the last dorsal rostral tooth (Table 1).

 

Fig. 1 Length variables measured in P. semisulcatus Note: Total length (TL): Tip of the rostrum-tip of telson, Sixth segment depth (SSD): Depth at the mid-point of the 6th segment, Second abdominal segment depth (SAD): Depth at the mid-point of the 2nd and 3rd segment, Partial carapace length (PCL): Posterior margin of orbit-posterior edge of carapace, Carapace width (CW): At the point of the last dorsal tooth.

 

Table 1 Measured variables (mm) and weight (g) of P. semisulcatus

 

The abdominal muscle tissue samples selected for the present study were homogenized (1 g/1 ml) in ice-cold DDW. After centrifuging at 6000 Xg for 30 minutes (-4º C), the supernatants were collected and stored in refrigerated condition (-20ºC) for further analysis. The supernatants were analyzed by Polyacrylamide gel electrophoresis (PAGE) using different percentages of gel, the band patterns (Zymogram) were detected by specific enzyme and protein staining procedures (Shaw and Prasad, 1970, Shaklee et al., 1990, Rebello, 2003, 2013, 2015a, b, c). Electrophoresis was carried out in vertical slab gel apparatus (GENEI-Bangalore). Discontinuous buffer system was used for the present study. Buffer systems with different pH and molarity were tried for the present study.
 

Among the four morphometric variables measured carapace width (CW) showed the highest correlation with the tail weight (TLW) (Table 2). Considerable differences are not seen in tail weight, indicating the samples collected from Kochi and Calicut belongs to a single morphological stock. Similar studies were observed in studies carried out in Merluccius merluccius (George, 1964), P. indicus (George, 1997; Paul, 2000) and in P. monodon (George, 1997; Rebello, 2003; Rebello et al., 2013, 2015a, b, c).

 

Table 2 Correlation Matrix between different morphometric characters of P. semisulcatus

  

Optimum results were obtained with 7% gel composition. The total length of gel was 130 mm. 4 mA current was used for each well. Time for migration was about 1-2 hours. Results were obtained as shown below.
 

Zymogram of protein in muscle tissues of P. semisulcatus shows 6 bands which were controlled by 4 loci (Fig. 2 and Plate 1) in which, the 1st and 3rd loci showed one band and 2nd and 4th loci showed 2 bands respectively.

 

Figure 2 Zymogram pattern of Protein profile in muscle tissue of P. semisulcatus of Kerala coast

 

Though the enzyme Aldehyde oxidase showed two zones of activity, only a single thick band developed (Fig. 3 and Plate 2). The allele AO-1*100 and AO-2*100 were accounted for the homozygous genotype.

 

Figure 3 Zymogram pattern of Aldehyde oxidase (AO) in muscle tissue of P. semisulcatus of Kerala coast

  

The ODH enzyme showed only one major zone of activity in P. semisulcatus (Fig. 4 and Plate 3). The allele ODH*100 accounted for homozygous genotype.

 

Figure 4 Zymogram pattern of Octanol dehydrogenase (ODH) in muscle tissue of P.semisulcatus of Kerala coast

 

The enzyme aldolase showed only one zone of enzyme activity. The zone showed three, two and single banded polymorphic phenotypes (Fig. 5 and Plate 4). The allele FBALD-1*100 accounted for the homozygous phenotype (100/100). The allele FBALD-1*87 accounted for the two banded heterozygous phenotype (87/100) and the allele FBALD-1*75 accounted for the three banded heterozygous phenotype (75/100). FBALD is monomeric in structure in P. semisulcatus.

Considerable differences in banding patterns were not found in the stocks obtained from Calicut and Kochi. This can be related to the fact that the genetic makeup is similar (Homozygous). However, morphologically, biochemical genetically and even molecular genetically defined subunits (Stocks) of fisheries management have been identified and reported with in many species of the maritime nations including that of India (Lester, 1990; Lester and Pante, 1992). A very small variation (FBALD*100/100; FBALD*100/120) was obtained from Calicut samples for FBALD, but there was no significant variation observed.
 

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Rebello V.T., George M. K., and Paulton M.P., 2015b, Population genetic stock structure of the Indian jumbo tiger prawn, Penaeus monodon Fabricius, 1798 from south-east and south-west coast of India, International Journal of Applied Research (in Press)

 

Rebello V.T., George M. K., Paulton M.P. and Ajith Joseph. C., 2015c, Allozyme markers of the jumbo tiger prawn Penaeus monodon Fabricius, 1798 from east and west coast populations of south India.  International Journal of Biosciences (in press)

 

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