New Distributional Record of Greater Amberjack Seriola dumerili (Risso, 1810) (Perciformes: Carrangidae) from the Eastern Arabian Sea, India

Background: The fishes of the family Carangidae forms one of the largest families of bony fishes, representing about 140 species, widely distributed in all tropical and temperate marine waters of the world. In recent past, fishes of this family are exhibiting new geographical distribution which could be attributed to climatic variability. Methods: The specimens were collected from multiday trawl boats operated along Karnataka coast. Morphometric and meristic characteristics together with genetic analysis using DNA bar coding was used to validate the identity of the specimen. Spatial distribution map of the species in Indian Ocean was generated using the information from the present study and available literature. Result: The morphometric and meristic characteristics of the specimens of greater amberjack, Seriola dumerili collected during the study were comparable with the previous investigations. The phylogenetic tree constructed using sequences of COI (MW974826 and MW974827) of the Seriola species showed distinct clustering among species with significant bootstrap values confirming the identity to the extent of 99% with the sequences of Seriola dumerili deposited in NCBI GenBank. This study confirms the first distributional record of Seriola dumerili from the eastern Arabian Sea.

Osmoregulatory Plasticity of Juvenile Greater Amberjack (Seriola dumerili) to Environmental Salinity

Osmotic costs in teleosts are highly variable, reaching up to 50% of energy expenditure in some. In several species, environmental salinities close to the isosmotic point (~15 psu) minimize energy demand for osmoregulation while enhancing growth. The present study aimed to characterize the physiological status related to osmoregulation in early juveniles of the greater amberjack, Seriola dumerili, acclimated to three salinities (15, 22, and 36 psu). Our results indicate that plasma metabolic substrates were enhanced at the lower salinities, whereas hepatic carbohydrate and energetic lipid substrates decreased. Moreover, osmoregulatory parameters, such as osmolality, muscle water content, gill and intestine Na+-K+-ATPase activities, suggested a great osmoregulatory capacity in this species. Remarkably, electrophysiological parameters, such as short-circuit current (Isc) and transepithelial electric resistance (TER), were enhanced significantly at the posterior intestine. Concomitantly, Isc and TER anterior-to-posterior intestine differences were intensified with increasing environmental salinity. Furthermore, the expression of several adeno-hypophyseal genes was assessed. Expression of prl showed an inverse linear relationship with increasing environmental salinity, while gh mRNA enhanced significantly in the 22 psu-acclimated groups. Overall, these results could explain the better growth observed in S. dumerili juveniles kept at salinities close to isosmotic rather than in seawater.

Evaluation of Praziquantel Efficacy against Zeuxapta Seriolae Infections in Greater Amberjack, Seriola Dumerili

The aim of this study was to evaluate the efficacy of dietary praziquantel (PZQ), a promising fish anthelminthic, against Zeuxapta seriolae, a lethal ectoparasite of greater amberjack (Seriola dumerili Risso) farmed in the Mediterranean and elsewhere. The trial was carried out in small cages (3 m3) in situ, harbouring fish (125 ± 14 g) naturally infected with Z. seriolae, at 25 ± 1 °C water temperature. Praziquantel-medicated diet (150 mg PZQ/kg fish) was delivered for three days against a control group. Measurement of both adults and oncomiracidia of Z. seriolae in sampled gill arches revealed significant differences between the tested groups (PZQ: 19.3 ± 9.8 vs. Control: 3.8 ± 6.3). Considering an estimated efficacy of 80.4% in the medicated fish, the present study indicates that oral PZQ treatments can confront Z. seriolae infections considerably in farmed greater amberjack and, perhaps, replace the commonly used hydrogen peroxidase baths.