The elasmobranchs (sharks, rays and skates) being the extant survivors of one of the earliest offshoots of the vertebrate evolutionary tree are good model organisms to study the primitive vertebrate conditions. They play a significant role in maintaining the ecological balance and have high economic value. Due to over-exploitation and illegal fishing worldwide, the elasmobranch stocks are being decimated at an alarming rate. Appropriate management measures are necessary for restoring depleted elasmobranch stocks. One approach for restoring stocks is implementation of conservation measures and these measures can be formulated effectively by knowing the evolutionary relationship among the elasmobranchs. In this study, a total of 30 species were chosen for molecular phylogeny studies using mitochondrial cytochrome c oxidase subunit I, 12S ribosomal RNA gene and nuclear Internal Transcribed Spacer 2. Among different genes, the combined dataset of COI and 12S rRNA resulted in a well resolved tree topology with significant bootstrap/posterior probabilities values. The results supported the reciprocal monophyly of sharks and batoids. Within Galeomorphii, Heterodontiformes (bullhead sharks) formed as a sister group to Lamniformes (mackerel sharks): Orectolobiformes (carpet sharks) and to Carcharhiniformes (ground sharks). Within batoids, the Myliobatiformes formed a monophyly group while Pristiformes (sawfishes) and Rhinobatiformes (guitar fishes) formed a sister group to all other batoids.

Compensatory growth has been reported in stunted fish by several researchers, and the same has been applied at field level for enhancing the fish production. Many of the commercially important marine finfishes such as European seabass (Adakli & Tasbozan, 2015),

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A study was conducted to compare the reproductive performance of Clarias batrachus (Linnaeus, 1758) collected from three different rivers viz., Krishna in Andhra Pradesh, Godavari in Maharashtra and Narmada in Madhya Pradesh. Twenty pairs of brooders from each location were randomly selected and induced with pituitary extract (P) and ovaprim (O). Reproductive performance in terms of stripping percentage, pseudo gonado-somatic index, spawning, fecundity, fertilisation rate, hatching rate, and survival rate as well as fry rearing performance in terms of percentage weight gain, specific growth rate (SGR) and survival rate were monitored. Brooders collected from Godavari exhibited significantly (p<0.05) higher values for all the reproductive performances indicators compared to brooders collected from Narmada and Krishna rivers. But fishes collected from Krishna River exhibited significantly higher (p<0.05) fry survival. Fry produced from Godavari brooders attained highest (p<0.05) percentage weight gain (1085.88±37.41), SGR (17.61±0.19) and fry survival rate (43.67±1.45) in comparison to Narmada. Results clearly indicated that reproductive performance varied significantly among the brooders collected from the three different rivers.

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Identification of elasmobranchs by conventional taxonomy is difficult due to similarities in morphological characters. Species-specific molecular markers are good choice for identifying species irrespective of it's life stage. Recently, mitochondrial cytochrome c oxidase subunit I (COI) gene got global recognition as a barcode gene to discriminate all animals up-to species level. In this study, mitochondrial COI partial gene was used to develop DNA barcodes for 18 species of elasmobranchs (10 species of sharks and 8 species of rays). The COI barcodes clearly distinguished all the species with high interspecific distance values than intraspecific values. The average interspecific and intraspecific distance values are 8.6% and 0.3% for sharks, respectively and 12.4% and 0.63% for rays, respectively using K2P method. The Neighbor-Joining tree showed distinct clusters shared by the species of same genera. The COI barcodes were also used to estimate allopatric divergences for selected species across broad geographical locations and found that Sphyrna lewini, Aetobatus narinari and Neotrygon kuhlii have cryptic diversity.