Taxonomy and Identification of Finfish Eggs from Muthupettai, South East Coast of India

The fish seed resource is a major input for fish farming. There is a playing important role for increasing fisheries production, providing food and income as well as contributing to national economy. Fishes is a delicious and most important source of animal protein food. Since, the fish seed resource is an essential for food security, rural development and poverty alleviation. In the present investigation fin fish eggs belonging to 43 species of finfishes belong to 31 genera, 19 families, 8 orders, have been collected, identified and described in detail. Among the various finfish eggs collected, higher number of eggs were recorded for Cluepeids fishes, followed by Engraulids, Carangids, Cynoglossids, Tetraodontids, Teraponis, Mugilids, Atherinids, Synodontids, Ophichthids, Pristigastrids, Chirocentrids, Scombrids, Gerreids, Soleids, Bothids, Pleuronectids and Hemiramphids from Muthupettai waters.


Introduction
The knowledge on the early development of fin fishes in Indian waters is incomplete and more information is needed on the early life history of a large number of species. The prospective values of the studies on the planktonic fish eggs and larvae have been widely recognised in recent years especially after standardisation of techniques for their rearing [1][2][3]. Availability of extensive information on the biology of edible fishes is an essential prerequisite before planning for their proper management [4,5] and for rational exploitation of these resources. For aquaculture practices, information on early developmental stages of commercially important finfishes is essential. However ichthyoplankton survey conducted over a period of two years along Muthupettai waters, few embryonic and early stages of fin fishes were collected and then visibly were identified.

Materials and Methods
The study was conducted at Muthupettai coast during between from January 2010 to December 2011. Finfish eggs were collected every month in the early hours of the day during high tide, with the help of plankton net of diameter 0.5 m made of bolting silk (No: 10 mesh size, 158 μm). Volume of water filtered was quantified with the help of a calibrated flow meter (General Oceanics, INC model) attached to it. The net was towed horizontally along the surface water at a constant speed of 1.0 km/hr for about 15-20 minutes in each station by adopting the method of [6,7]. Samples from all the stations were preserved onboard in 5% buffered formalin-seawater and sorted in the laboratory [8]. For identification of finfish eggs, the earlier investigations made by Delsman, Vijayaraghavan, Bensam, Job, Jones, and Venkataramanujam [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] were consulted. The photographs were taken by using a Sony Camera Measurement was taken micrometer fixed in the microscope.
in lower bony fishes, yolk is vacuolated or segmented and a wide perivitelline space is present such as clupeoid fishes (Figures 3 and 4).

Membrane:
The outer egg membrane (chorion) in most marine fishes is smooth and unornamented, but in few eggs, it is ornamented. For example, eggs belonging to the order Synodontiformes, the egg membrane has a honey comb-like polygonal network on the outer surface. The eggs of Myctophiformes have the spine like structure on the chorion. Hemiramphids and Exocoetids have the adhesive filaments ( Figures 5 and 6).
Size of the egg: According to Ramaiyan et al. [26], most of the marine fish eggs (especially planktonic eggs) are in the size range of 0.5-4.0 mm in diameter. Bothid flat fishes have the small eggs, the size ranges between 0.5 to 0.8 mm whereas, Pleuronectid flat fishes have large eggs ranging from 4.0 to 4.5 mm; eels have still larger eggs of about 5 mm in size. In eels, the large size may be due to hydration of the egg and the progressive development of Perivitelline space.
Majority of the planktonic marine finfish eggs are spherical in shape. For example, fishes belonging to the orders Clupeiformes, Mugiliformes, Aulopiformes, Atheriniformes, Perciformes, Pleuronectiformes and Tetraodontiformes have spherical eggs. Few eggs are ellipsoidal in shape; for example, fishes belonging to the family Engraulidae the eggs are ellipsoidal in shape. Eggs of Stolephorus indicus and S. commersoni are provided with a knob-like structure at one pole (Figures 7 and 8).

Results and Discussion
Taxonomical position of species: Classification of the fishes whose eggs are dealt with in the present work and their placement in Families    as well as other taxa are largely as per the classification followed by Nelson [27][28][29]. Nomenclature of Subfamilies in Family Clupeidae is as per Whitehead [30] for other families as given by Nelson [28,29]. For the identification of fin fish eggs the methodology followed by previous workers such as Delsman, Vijayaraghavan, Job, Jones, Venkataramanujam, Whitehead and Nair [9][10][11][12][13][14][15][16][17]19,23,25,30,31]

Descriptions of the species
Ophichthys sp. (Snake eels): Eggs of Ophichthys sp. are pelagic, rounded, colorless and transparent. Diameter ranges from 2.30-2.80 mm. Yolk is spherical, colorless, transparent and segmented. A single, yellowish oil globule, measuring the diameter of 0.5 mm and it is located opposite to the developing embryo in the yolk mass. Perivitelline Space is large. Nature of the Chorion is smooth and unpigmented. Identification of these eggs is based on the previous works of Delsman, Ramaiyan et al., Ganapati,Raju,and Manickasundaram [17,26,[32][33][34].

Chirocentrus dorab (Forsskal, 1775), (Dorab wolf-herring):
C. dorab eggs are pelagic, rounded, colorless and transparent. Egg diameter ranges between 1.68-1.72 mm (egg is easily recognized by their large size). Yolk mass is spherical, segmented, colorless and transparent, the yolk diameter ranges between 1.21-1.30 mm. 7-19 small sized oil globules are distributed irregularly in the yolk. Perivitelline width is narrow. The Egg membrane is not smooth but has on its surface a network of fine ridges which give it a honey comb appearance. Unpigmented in nature. These eggs are identified based on the works of Delsman, Ramaiyan et al. and Manickasundaram [9,26,34].
Nematolosa nasus (Bloch, 1795) (Long-ray bony bream): Eggs of N. nasus are pelagic, spherical, colorless and transparent. Egg diameter ranges between 0.94-1 mm. Yolk is spherical, colorless, transparent and vacuolated, the vacuoles being fairly large in size. Golden yellow, uneven sized eight oil globules are present; the size ranging between 0.036-0.081 mm. Usually the oil globules are found near the tail of the embryo. Perivitelline width is narrow. Pigmentation is absent in early eggs, but in late stages of the embryonic development, a few black pigment spots are noted on the dorsal side of the embryo. These eggs were identified based on the works of Job, John and Ramaiyan et al. [23,26].

Saurida gracilis (Quoy and Gaimard, 1824) (Slender lizard -fish):
Eggs of S. gracilis are pelagic, perfectly spherical, colorless and transparent and an average egg measuring 1.02 mm in diameters. Yolk shape is spherical, clear, unsegmented filling practically the entire surface inside the egg membrane. Single colorless and transparent oil globule located at the centre of the yolk. Perivitelline width is narrow. Envelop is ornamented, fine network of hexagonal meshes are found on the surface of the egg membrane, the average mesh size being 0.03 mm. The fine net-work of ridges on the egg membrane affords additional protection to the egg which is necessary for the longer time taken for the development of the embryo. In the mid stages of developing embryo, the embryo is fairly large in size and occupies the whole of the egg surface. The eyes and auditory vesicles are clearly seen. The heart has begun to beat very slowly and myotomes are faintly discernible. The trunk and tail regions of the developing embryo are also well developed. Pigmentation is absent. Identification is based on the works of Delsman, Venkataramanujam and Ramaiyan et al. [18,[24][25][26].
Saurida tumbil (Bloch, 1795) (Common saury): S. tumbil eggs are pelagic, spherical, colorless, transparent and measuring 1.12 mm in diameter. Yolk is spherical, colorless, transparent, unsegmented and filling practically the entire space inside the egg membrane. Perivitelline width is narrow. Egg membrane is thin and ornamented, marked by network of hexagonal meshes of approximately equal size on the outer surface of the egg membrane. The hexagonal meshes project in the form of ridges, which are easily seen when viewed from the side, measuring 0.034 mm across. Pigments and Oil globules are absent. The embryo appears fairly large, with well developed head, trunk and tail regions. The eyes and the auditory vesicles are distinct. Identification of these eggs is based on the previous works of Venkataramanujam, Abukhair Mohammad Mohsin and Mohd Azami Ambaki [24,25,39].

Saurida sp. (Lizard fishes):
Saurida eggs are pelagic, spherical, colorless and transparent, measuring 2 mm in diameter. Yolk is spherical, unsegmented, colorless and transparent; the diameter being 1.98 mm. Perivitelline widths is narrow. Net-work of hexagonal meshes is found on the egg membrane. Pigments are absent. The identification is based on the earlier work of Delsman and Ramaiyan et al. [18,26].

Saurus sp. (Lizard fishes):
Saurus sp. eggs are pelagic, spherical, pale whitish in color and measuring 1.12 mm in diameter. Yolk is spherical, granular, colorless and transparent; the diameter being 0.98 mm. 21 (22)(23)(24)(25)(26)(27)(28) oil globules are present, of these; 6-8 are large in size, the size ranging between 0.038-0.076 mm, the average oil globule diameter being 0.05 mm. These oil globules are irregularly distributed in the yolk. Perivitelline width is narrow. Bold hexagonal marking present on the egg membrane, distance between 2 opposite sides is 0.288 mm, thickness of hexagons 0.0288 mm, 29 ridges are present on the surface of the egg membrane, the distance between 2 ridges is 0.11-0.18 mm. Few melanophores present on the dorsal side of developing embryo and few stellate chromatophores are present on the yolk. Identification is based on the works of Bapat, Delsman, Venkataramanujam and Ramaiyan et al. [1,18,[24][25][26].
Synodontid Egg: Egg of Synodontid is pelagic, spherical, colorless and transparent; the average diameter being 2.05 mm. Yolk is spherical, granular, colorless and transparent; the average diameter being 1.99 mm. Single, colorless and transparent oil globule situated at the center of the yolk, the average measuring 0.44 mm in diameter. Perivitelline width is narrow. Bold hexagonal markings are present on the surface of the egg membrane, 17 ridges are present on the egg membrane, which affords additional protection to the egg which is necessary by the longer time taken for the development of the embryo. Unpigmented in nature. Identification of this egg is based on the work of Delsman and Ramaiyan et al. [18,26].

Liza dussumieri (Valenciennes):
These eggs are pelagic, globular, colorless and transparent; the diameter ranging between 0.53-0.57 mm and the average diameter being 0.55 mm. Yolk is spherical, clear, colorless, transparent and unsegmented. Single oil globule is occupying the head portion of the developing embryo. The size range of the oil globule is between 0.154-0.1.65 mm and the average diameter being 0.15 mm. Perivitelline width is narrow. Pigments are present on the developing embryo; two patches of light yellowish brown pigments in the head region and black pigments intermingled with light yellowish brown chromatophores on the trunk and tail regions and similar pigment spots were noticed on the oil globule also. In early stage, the head, trunk and tail are not clearly visible. Identification of these eggs is based on the work of Job, John and Ramaiyan et al. [23,26].  [26,40,41].
Pranesus pinguis (Lacepede, 1803) (Silver side): P. pinguis eggs are pelagic, spherical, without any sculpture, colorless and transparent and the average diameter of the egg being 0.59-0.62 mm. Yolk is spherical and unsegmented measuring a diameter of 0.514-0.518 mm. Oil globules is absent. Perivitelline width is very narrow. Spot like black pigments are found scattered all over the egg and punctuate black pigments found scattered from the head to near the caudal region of the developing embryo. The embryo is very prominent with head (primordial brain, eyes and auditory vesicles) trunk (tubular heart) and tail, the developing eyes are very prominent but without pigmentation. These eggs were identified based on the works of Ramaiyan et al., Nelson,Thangaraja and Manickasundaram [26,28,32,34].  [1,[24][25][26]36] were consulted for the identification of these eggs.  [1,11,[24][25][26]32] were employed for the identification of the eggs.

Carangoides malabaricus (Bloch and Schneider
Decapterus russelli (Ruppell, 1830) (Indian shad): D. russelli eggs are pelagic, spherical, colorless and transparent, the size ranging between 0.7-0.76 mm in diameter. Yolk is spherical, slightly segmented, colorless and transparent, diameter being 0.58 mm. Single and prominent, yellowish-brown colored oil globule is ventrally situated; the size being 0.14 mm in diameter, it has faint yellow tinge. Perivitelline width is narrow. Oil globule with numerous, thick brown punctate and filament like pigments, punctate brown pigments present all over the dorsal and ventral surface of the embryo from snout to caudal region of the developing embryo. Few stellate pigments are present on the head region of the developing embryo. On the trunk region of the developing embryo, black and yellow chromatophores are alternating each other. The developing embryo is well developed but the caudal region is free from the yolk mass and capable of moving occasionally. Previous works done by Delsman, Ramaiyan et al. and Manickasundaram [15,26,34] was used to identify the eggs.  [23,26] described these eggs and his work was consulted.

Secutor ruconius (Hamilton, 1822) (Deep pug nose pony fish):
Eggs of S. ruconius are pelagic, spherical, colorless and transparent measuring 0.66-0.68 mm in size (average: 0.67 mm). Yolk is spherical, unsegmented located at the centre of the egg. The average diameter of the yolk being 0.652 mm. Single and prominent oil globule, present at the center of yolk, measuring 0.17 mm in diameter. Perivitelline width is very narrow and unpigmented in nature. The work of Ramaiyan et al. and Thangaraja [26,32] was used to identify the eggs.  [21][22][23]26,32,34,38] were used for the identification of these eggs.  [11,[24][25][26]34,36] were used for the identification of the eggs.
Pleuronectid Egg: Pleuronectid eggs are pelagic, spherical, colorless and transparent, measuring a diameter of 4.05-4.85 mm. Yolk is spherical, unsegmented, colorless and transparent in nature. Oil globules are absent. Pigmentation is absent. In late stage of embryonic development, the developing embryo is fully developed with eyes, auditory vesicle and with distinct head, trunk and tail region. Caudal region of embryo is free from the yolk Ramaiyan et al. and Matarese et al. [26,42] were used for the identification of these eggs.  [26,31,32] were used for the identification of the eggs.

Cynoglossus arel (Bloch and Schneider, 1801) (Brown tonguefish):
C. arel eggs are pelagic, spherical, colorless and transparent, measuring 0.64-0.66 mm in size. Yolk is spherical, unsegmented, colorless and transparent. 20-30 oil globules are concentrated at the anterior side of the egg, the oil globules are mostly smaller in size and some are relatively larger. The diameter of the oil globule ranges from 0.03-0.06 mm. Perivitelline widths is very narrow and pigments are absent. The blastoderm has already spread over the surface of the yolk and appears as a cap surrounding the yolk. Works of Bapat, Venkataramanujam, Ramamoorthi, Ramaiyan et al., Thangaraja and Balakrishnan [1,[24][25][26]32,43] were used for the identification of these eggs.
Cynoglossus puncticeps (Richardson, 1846) (Speckled tongue sole): C. puncticeps eggs are pelagic, perfectly spherical, colorless and transparent and the average size measuring 0.67 mm in diameter. Yolk is spherical, unsegmented, colorless and transparent measuring a size of 0.656 mm. Number of oil globules are varied from 15 -18. These oil globules are uneven in size; the average size being 0.012 mm. Mostly, these oil globules are spread all over the yolk and located at the centre of the yolk. Quite narrow perivitelline width. Embryo developes without any pigmentation on its body, 16 somites and rudiments of eyes are discernable. Venkataramanujam, Ramamoorthi, Ramaiyan et al. and Thangaraja [24][25][26]32] works were employed for the identification of these eggs.

Arothron hispidus (Linnaeus, 1758) (White-spotted puffer):
Eggs of A. hispidus are pelagic, spherical, colorless and transparent, measuring 1.49 mm in diameter. Yolk is spherical, unsegmented, colorless and transparent. Single, pale yellow oil globule is present in the yolk, measuring 0.430 mm in size. Perivitelline width is narrow in lateral side (0.122 mm) and wide in anterior and posterior sides (0.149 mm). Prominent, black pigments present on the oil globule. In developing embryo, the body somites are not prominent but are marked by the pigments. Auditory vesicles and unpigmented eyes have also appeared. Works of Ramaiyan et al., Jones, Thangaraja, Sundaramanickam et al. and Prabhu [26,27,32,44,45] were consulted for the identification of these eggs.

Arothron sp. (Blowfish):
Eggs of Arothron sp. are pelagic, spherical, colorless and transparent; average egg diameter is 1.42 mm. Yolk is spherical, unsegmented and the average yolk diameter is 1.11 mm. A single, light yellowish oil globule is present, the size measuring from 0.27-0.30 mm. Perivitelline width is narrow. Yolk is fully brownish pigmented. Four branched stellate chromatophores are present on the oil globule and brown pigments on the yolk. The sides of the embryo are deeply pigmented and few chromatophores are seen at the tail region of the developing embryo. The development of auditory vesicle and eyes could be seen clearly in the embryo. Works of Venkataramanujam, Ramaiyan et al., Jones, Thangaraja and Manickasundaram [24][25][26][27]32,34] were used for the identification of the eggs.
Mangrove has a generally been recognised as nursery and feeding grounds for most of the fishes. In the modern days, aquaculture is a fastest growing industry throughout the world to increase the fishes productions mainly in coastal aquaculture. Climatic or weather conditions are mainly affecting the species distribution from marine environment still, the favorable conditions occurs on the ecosystem because of the most organisms tolerate unfavorable conditions. Advance technology of finfish seed production as by induced breeding is sometimes fairly or absence, though the reason of genetic deterioration. Though, the collection of seeds are well from the natural environments are only the major source at present. Therefore, Muthupettai mangrove environment is one of the rich grounds for the finfish eggs resources. Some species in eggs are localized while others have a wide range of distribution. The density of fin fish eggs at all stations showed a seasonal variation. The maximum number of eggs were recorded during postmonsoon followed by premonsoon, summer and monsoon seasons. The seasonal occurrence of finfish eggs did not follow a similar pattern during the two-year period of study. This might be due to the fluctuation in the environmental parameters. The study was providing information on the sampling stations should be avoiding drainage wastes and some other pollution illegally releasing from the environment. There urgently be required prober management and further scientifical research for maintain the survive of species and safe demand of food.