STUDIES ON FISH EGGS AND LARVAE IN NEARSHORE WATERS OF GULF OF MANNAR, TAMIL NADU

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Date
2019
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Fisheries College and Research Institute, Thoothukudi, Tamil Nadu Dr. J. Jayalalithaa Fisheries University
Abstract
The present investigation was conducted to study the diversity, distribution, spawning season of fishes, molecular identification of fish eggs and larvae and distribution of fish eggs and larvae based on GIS mapping at Mandapam, Thoothukudi and Punnakayal in Gulf of Mannar from September 2017 to May 2019. A total number of 26,092 fish eggs were collected and 48 species were identified from all the studied stations in the nearshore waters of Gulf of Mannar during the study period. Eggs of Atherinomorus lacunosus, Callionymus sp., Amblygaster leiogaster, Hilsa kelee, Sardinella longiceps, S. jussieu, Carangoides malabaricus, Decapterus russelli, Setipinna taty, Hirundichthys coromandelensis, Hemiramphus sp., Planiliza macrolepis, Ophisurus macrorhynchos, Echelus sp., Pseudorhombus javanicus, Rastrelliger kanagurta, Scomberomorus commerson, Saurida tumbil, Arothron sp. and Sphyraena sp. were collected for the first time in the nearshore waters of Gulf of Mannar. A total number of 5,100 fish larvae were collected and 23 species were identified from all the three stations in Gulf of Mannar. Larvae of Hypoatherina valenciennei, Oryzias dancena, Etroplus suratensis, Planiliza macrolepis, Alepes djedaba, Atule mate, Gerres erythrourus, Auxis rochei rochei, Katsuwonus pelamis, Pelates quadrilineatus, Terapon puta, Bothus sp., Cynoglossus arel, Cociella crocodilus and Halicampus grayi were collected for the first time in the waters of Gulf of Mannar. The laboratory development of the Mugil cephalus from egg to the just hatched larval stage has been studied. The eggs were found to be abundant at Punnakayal and Thoothukudi and larvae were found to be more abundant at Thoothukudi. Maximum number of fish eggs and larvae were recorded during 2018 compared to 2017 and 2019. The monthly occurrence of fish eggs and larvae revealed that they were generally abundant during October, March, July and August. Eggs of Caranx sp., Cynoglossus semifasciatus and larvae of Mugil cephalus, Chanos chanos and Terapon jarbua occurred throughout the year. It was observed that the most of the fishes were found to spawn during post monsoon at Mandapam, summer and post monsoon at Thoothukudi and Punnakayal. 19 families of fish eggs and 16 families of fish larvae were recorded from all the three stations. Clupeidae was the most dominant fish egg family (50.99%) at Mandapam and family Cynoglossidae contributed the maximum at Thoothukudi and Punnakayal (38.24%), (53.22%). Mugilidae was the dominant fish larvae family at Mandapam and Punnakayal contributing to 72.35% and 46.50% respectively, whereas larvae of Terapontidae (53.82%) contributed the maximum at Thoothukudi. During the study period, a total of 36 species of zooplankton representing 8 phyla, 10 classes, 13 orders, 20 families and 32 genera were recorded from all the three stations. Maximum zooplankton density 41624.2 no./100m3 was observed at Thoothukudi. Copepoda was the most dominant group of zooplankton at all the three stations. Zooplankton diversity indices were calculated for Margalef’s species richness (0.41 to 0.42), Pielou’s evenness (0.42 to 0.60) and Shannon-Wiener species diversity (1.10 to 1.55). The results indicated high zooplankton diversity in Mandapam. The ranges of fish eggs diversity indices calculated during study period were Shannon-Wiener species diversity (3.503 to 4.52), Margalef’s species richness (3.016 to 5.584), Pielou’s evenness (0.9616 to 0.977), Average taxonomic distinctness (88.26 to 92.92) and Total phylogenetic diversity (925 to 1800). The calculated ranges of fish eggs diversity indices indicated healthy nature of ecosystem with rich species diversity in descending order from Punnakayal followed by Thoothukudi and Mandapam. The ranges of fish larval diversity indices calculated during study period were Shannon-Wiener species diversity (2.021 to 2.357), Margalef’s species richness (1.424 to 1.696), Pielou’s evenness (0.7199 to 0.7855), Average taxonomic distinctness (95.24 to 99.11) and Total phylogenetic diversity (625 to 1275). The calculated ranges of fish larval diversity indices indicated healthy nature of ecosystem with rich species diversity in descending order from Thoothukudi followed by Mandapam and Punnakayal. The environmental parameters were recorded at all three stations and the rainfall ranged from 65.53±95.94 mm to 109.09±155.06 mm, water temperature from 25.61±2.23°C to 27.42±3.44°C, salinity from 32.61±1.9 to 35.71±2.8, pH from 7.59±0.34 to 7.83±0.30 and dissolved oxygen from 4.31±0.90 to 5.14±0.95 mg/l. Maximum egg density 1658.58 no./100m3 was observed at Punnakayal and maximum larval density 270.20no./100m3 at Thoothukudi. All the water quality parameters were found to be within the levels prescribed for coastal waters.The variations in fish eggs and larvae at different stations in the Gulf of Mannar during different months were studied and correlated with various environmental parameters and zooplankton. It was found that water temperature, salinity and abundance of zooplankton play significant role in the distribution of fish eggs and larvae in Gulf of Mannar. Family wise fish eggs and larvae and group of zooplankton abundance were determined for Mandapam, Thoothukudi and Punnakayal during 2017-2019 in Gulf of Mannar. The correlation between fish eggs family and zooplankton group were found to be significant (p<0.01) at Thoothukudi and Punnakayal and correlation between fish larval family and zooplankton group were found to be significant (both p<0.01 and p>0.05) at all three stations. From the occurrence of fish eggs and larval stages it can be inferred that fishes such as Caranx sp., Chanos chanos, Cynoglossus arel, Cynoglossus semifasciatus, Escualosa thoracata, Mugil cephalus and Terapon jarbua species appear to be continuous breeders in the waters of Gulf of Mannar; fishes such as Encrasicholina heteroloba, Pseudorhombus javanicus appear to spawn thrice in a year and some fishes like Amblygaster leiogaster, Arothron sp., Anodontostoma chacunda, Auxis rochei rochei, Bothus sp., Callionymus sp., Carangoides malabaricus, C. praeustus, Decapterus russelli, Dussumieria elopsoides, Echelus sp., Etroplus suratensis, Gerres erythrourus, Hemiramphus sp., Hilsa kelee, Hirundichthys coromandelensis, Hypoatherina valenciennei, Ophisurus macrorhynchos, Opisthopterus tardoore, Pelates quadrilineatus, Planiliza macrolepis, P. subviridis, Platycephalus indicus, Rastrelliger kanagurta, Sardinella fimbriata, S. jussieu, Saurida tumbil, Scomberomorus commerson, Setipinna taty, Sphyraena sp., Terapon puta and Thryssa dussumieri appear to spawn once in a year. Maturity stages of fishes were observed and correlated with abundance of eggs and larvae. It was found that when matured stocks were available that time occurrence of fish eggs and larvae were also present in Gulf of Mannar. The COI sequence of eggs of Thryssa hamiltonii, Planilza macrolepis, P. subviridis and Sardinella jussieu and larvae of Carangoides praeustus, Chanos chanos, Gerres erythrourus, Hypoatherina valenciennei, Pelates quadrilineatus and Terapon puta were generated from the Thoothukudi and Punnakayal waters. GIS based distribution of fish eggs and larvae has been studied at all the three stations. The abundance of fish eggs were in higher proportions in the nearshore waters off Punnakayal during summer and the aggregations of larvae in Gulf of Mannar was the highest in the nearshore waters of Thoothukudi and Mandapam during summer. Considering all, the environmental parameters, zooplankton and fish eggs and larval diversity and distribution of the studied stations reflected good water quality with high potential fish eggs and larval yields. As per the study on fish eggs and larvae, Punnakayal and Thoothukudi are the most productive water body followed by Mandapam in Gulf of Mannar. In the Gulf of Mannar, fish eggs and larvae were observed almost in every month at Punnakayal and Thoothukudi compared to Mandapam, indicating that Punnakayal and Thoothukudi region is probably a suitable spawning ground for many species. Occurrence of fish eggs during summer may be due to the peak spawning activities of these fishes coinciding the fishing holiday declared by the coastal state government with a view to enhance the breeding and spawning activities of these fishes. COI barcodes are essential to verify the species identification of fish eggs and larvae, especially of morphologically similar species. In the present study, COI barcodes were generated for the eggs of Thryssa hamiltonii, Planiliza macrolepis, P. subviridis and Sardinella jussieu and larvae of Carangoides praeustus, Chanos chanos, Gerres erythrourus, Hypoatherina valenciennei, Pelates quadrilineatus and Terapon puta collected from Thoothukudi and Punnakayal.
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