Showing papers by "National Institute of Oceanography, India published in 2007"

New Computations of the Tide‐generating Potential

Abstract: Summary A time-harmonic expansion of the gravitational tide potential is computed using an ephemeris of high precision for the Moon and the Sun and the latest I.A.U. astronomical constants. The results, which are computed for three different epochs and by novel methods, are compared with Doodson's classic expansion. The chief differences are due to secular trends in large terms and to revised constants which reduce all the solar terms. A new expansion is also given for the radiational tide potential.

Basin-wide seasonal evolution of the Indian Ocean's phytoplankton blooms

Abstract: A climatology of Sea-viewing Wide Field-of-View Sensor (SeaWiFS) chlorophyll data over the Indian Ocean is used to examine the bloom variability patterns, identifying spatio-temporal contrasts in bloom appearance and intensity and relating them to the variability of the physical environment. The near-surface ocean dynamics is assessed using an ocean general circulation model (OGCM). It is found that over a large part of the basin, the seasonal cycle of phytoplankton is characterized by two consecutive blooms, one during the summer monsoon, and the other during the winter monsoon. Each bloom is described by means of two parameters, the timing of the bloom onset and the cumulated increase in chlorophyll during the bloom. This yields a regional image of the influence of the two monsoons on phytoplankton, with distinct regions emerging in summer and in winter. By comparing the bloom patterns with dynamical features derived from the OGCM (horizontal and vertical velocities and mixed-layer depth), it is shown that the regional structure of the blooms is intimately linked with the horizontal and vertical circulations forced by the monsoons. Moreover, this comparison permits the assessment of some of the physical mechanisms that drive the bloom patterns, and points out the regions where these mechanisms need to be further investigated. A new outcome of this study is that in many distinct areas, time shifts of 1-2 months are witnessed in the timing of the bloom onsets in adjoining regions. These time shifts are rationalized in terms of horizontal advection and Rossby wave propagation.

Monsoonal impact on planktonic standing stock and abundance in a tropical estuary (Cochin backwaters – India)

Abstract: Environmental studies in the Cochin backwaters (CBW), a tropical estuary along the southwest coast of India showed that seasonal fluctuations in salinity created by the monsoonal rainfall and associated run off is a major factor controlling the distribution and abundance of micro- and mesozooplankton. During premonsoon season, the CBW was characterized by warm waters (av. 32.6 ± 0.6 °C) with relatively high salinity (>23; except in the lower estuary). On the other hand, fresh water was found to dominate the entire area during monsoon and postmonsoon seasons. The enormous input of nutrients (nitrate, phosphate and silicate) into the estuary from various sources (industries, agriculture and domestic) was responsible for the high phytoplankton biomass (av. 10.4 ± 10.1 mg m−3) irrespective of seasons. The phytoplankton community was, in general, dominated by diatoms (av. 88 ± 12%), and proliferation of multiple species of diatoms (Skeletonema costatum, Thalassiosira subtilis and Nitzschia closterium – 1600 × 103 cells L−1) at different locations were observed especially during high saline condition. In case of zooplankton (micro- and meso), high standing stocks (micro av. 81.4 ± 48.1 mg C m−3; meso av. 88 ± 125 mg C m−3, respectively) were recorded during the premonsoon season. Copepods (e.g. Calanoids) formed the abundant group (av. 75 ± 18%) in the mesozooplankton community irrespective of seasons. The ratio of carbon content between phytoplankton and zooplankton (P:Z) was quite high (>100) during monsoon and postmonsoon seasons, but became low during premonsoon season (

Observed seasonal variability of barrier layer in the Bay of Bengal

Abstract: [1] The observed formation of barrier layer (BL) and the seasonal variability of BL thickness (BLT) in the Bay of Bengal are examined utilizing the most comprehensive data set. Thick BL (∼40 m) first appears in the coastal region of the northeastern bay in June and spreads westward as the summer monsoon progresses. Along the east coast of India the BL formation and its variability are controlled by the East India Coastal Current (EICC). Thick BL (∼50 m) appears along the east coast of India in November when the EICC flows equatorward and gets spatially organized by December. By January it weakens when the EICC reverses. The mature phase of BLT, both in amplitude (∼60 m) and in spatial extent occurs during February, when the Subtropical Anticyclonic Gyre (SAG) is well established in the bay. During both the summer and winter monsoon seasons the surface circulation and the redistribution of low saline waters show a dominant influence on the observed BLT distribution. Other processes such as Ekman pumping and propagating Rossby waves forced by the propagating Kelvin waves along the eastern boundary also contribute significantly in modulating its variability. The annual mode of BLT shows maxima during November–December, whereas the semiannual mode peaks during February–March and August–September. The peak in February–March is attributed to the interior Ekman pumping and the associated convergence in the central bay, whereas the peak during August–September is due to the westward propagating downwelling Rossby waves from the eastern boundary.

Eddy-mediated biological productivity in the Bay of Bengal during fall and spring intermonsoons

Abstract: The signature of cold-core eddies and their role in altering the biological productivity of the Bay of Bengal was examined using two recent sets of hydrographic data collected along the central and western Bay of Bengal during fall (14 September – 12 October, 2002) and spring (12 April – 7 May, 2003) intermonsoons under the Bay of Bengal Process Studies (BOBPS) programme. Based on the thermohaline structure and the satellite-derived sea-level anomaly maps 9 cyclonic eddies were identified. Out of this, 4 cyclonic eddies – 2 each along the central Bay and along the western boundary – occurred during fall intermonsoon 2002, while 5 occurred – 3 along the central Bay and 2 along the western boundary – during spring intermonsoon. The eddy depressed the temperature, which varied from 3 o C to 7 o C at 120 m depth. Maximum depression of temperature was associated with spring-time eddies in the northern Bay, where subsurface stability was low. The reduced water column stability in spring leads to greater eddypumping, thereby cooling the water to a greater extent. However, the cyclonic eddies were unable to break the stratification of the top 20m layer, thereby curtailing their effects below this depth during both seasons. Eddypumping not only cooled the water column but also enhanced the nutrient concentrations. This in turn increased the biological productivity of the Bay to 1½-2 times. In addition, the subsurface chlorophyll maximum (SCM), which is generally located between 40 and 70 m in fall and 60 and 90 m in spring intermonsoons, shallowed under the influence of the eddies and also enhanced the chlorophyll concentration in the SCM to more than double. Thus, eddy-pumping of nutrients controls the biological productivity of the Bay of Bengal during both the seasons. In the fall intermonsoon, however, the riverine input of nutrients and sediments in the northern Bay also plays a role in altering the biological productivity. This has an overall implication to the basin-wide new production and export flux and, at least partly, resolves the reason for the comparable annual fluxes of organic carbon

Application of remote sensing and GIS for the demarcation of groundwater potential zones of a river basin in Kerala, southwest coast of India

Abstract: An integrated hydrogeological investigation has been made to delineate the groundwater-potential zones of the Muvattupuzha river basin, Kerala, along the southwest coast of India. The basin is characterized by charnockites and gneisses of Archean age covering more than 80% of the area and the remaining by Pleistocene laterites and Miocene formation. The basin receives high rainfall, measuring 3100 mm/year. However, acute water shortage occurs during the premonsoon season and hence, a number of dug wells are made to tap the groundwater. Seasonal rainfall during NE and SW monsoons is the major source of groundwater recharge. Further, hydrogeomorphology, geology, fracture systems and the slope of the terrain also play a significant role on the movement and behaviour of the groundwater of this basin. The integration of conventional and remote sensing data has been made through geographic information system (GIS) and it is found that about 50% of the area can be identified as very good or good potential zones, whereas the remaining area falls under moderate and poor categories. Most of the Muvattupuzha sub-basin and the western part of the Kothamangalam and Kaliyar sub-basins are classified as good groundwater-potential zones, although the eastern upstream part of the basin has poor groundwater potential.

Improved bathymetric datasets for the shallow water regions in the Indian Ocean

Abstract: Ocean modellers use bathymetric datasets like ETOPO5 and ETOPO2 to represent the ocean bottom topography. The former dataset is based on digitization of depth contours greater than 200 m, and the latter is based on satellite altimetry. Hence, they are not always reliable in shallow regions. An improved shelf bathymetry for the Indian Ocean region (20°E to 112°E and 38°S to 32°N) is derived by digitizing the depth contours and sounding depths less than 200 m from the hydrographic charts published by the National Hydrographic Office, India. The digitized data are then gridded and used to modify the existing ETOPO5 and ETOPO2 datasets for depths less than 200 m. In combining the digitized data with the original ETOPO dataset, we apply an appropriate blending technique near the 200 m contour to ensure smooth merging of the datasets. Using the modified ETOPO5, we demonstrate that the original ETOPO5 is indeed inaccurate in depths of less than 200 m and has features that are not actually present on the ocean bottom. Though the present version of ETOPO2 (ETOPO2v2) is a better bathymetry compared to its earlier versions, there are still differences between the ETOPO2v2 and the modified ETOPO2. We assess the improvements of these bathymetric grids with the performance of existing models of tidal circulation and tsunami propagation.

Effect of totally or partially replacing fish meal by alternative protein sources on growth of African catfish Clarias gariepinus (Burchell, 1822) reared in concrete tanks

Abstract: A 12-week feeding trial was carried out in concrete tanks to examine complete and partial replacement (75%) of fish meal (FM) with poultry by-product meal (PBM), meat and bone meal (MBM) and soybean meal (SBM) in practical feeds for African catfish Clarias gariepinus. Triplicate groups of fish (initial body weight ranged from 90.33 to 93.93 g fish−1) were fed seven isonitrogenous and isocaloric diets of 20% digestible protein and 300 kcal 100 g−1 of digestible energy. The control contained 25% herring meal, whereas in the other six diets, PBM, MBM and SBM replaced 75% or 100% of the FM. Final body weight (FBW) and specific growth rate (SGR) of the fish fed diets containing PBM (75% and 100%), SBM (75% and 100%) and MBM (75%) were all higher, but not significantly different than those for fish fed the control diet. Replacing 100% of the FM by MBM significantly lowered FBW and SGR. Concerning whole body composition, there were no significant differences in ash and gross energy content of whole-body among fish; fish fed diets containing PBM-100% recorded significantly lower protein content compared with the control diet, while fish fed diet SBM-100% recorded significantly lower moisture content compared with the control diet. Also fish fed diets SBM-100% and PBM-75% recorded higher lipid and gross energy contents compared with the control diet. The study revealed that satisfactory growth and feed utilization responses could be achieved through the replacement of FM by PBM, SBM and MBM in the diet of African catfish.

Stress effect of different temperatures and air exposure during transport on physiological profiles in the American lobster Homarus americanus.

Abstract: Homarus americanus is an important commercial species that can survive 2–3 days out of water if kept cool and humid. Once caught for commercial purpose and shipped around the world, a lobster is likely to be subjected to a number of stressors, including emersion and air exposure, hypoxia, temperature changes and handling. This study focused on the effect of transport stress and specifically at different animal body temperature (6 and 15 °C) and air exposure during commercial transport and recovery process in water. Animals were monitored, by hemolymph bleeding, at different times: 0 h (arrival time at plant) 3 h, 12 h, 24 h and 96 h after immersion in the stocking tank with a water temperature of 6.5 ± 1.5 °C. We analysed the effects by testing some physiological variables of the hemolymph: glucose, cHH, lactate, total protein, cholesterol, triglycerides, chloride and calcium concentration, pH and density. All these variables appeared to be influenced negatively by high temperature both in average of alteration from the physiological value and in recovering time. Blood glucose, lactate, total protein, cholesterol were significantly higher in the group with high body temperature compared to those with low temperature until 96 h after immersion in the recovery tank.

Simulated Seasonal and Interannual Variability of the Mixed Layer Heat Budget in the Northern Indian Ocean

Abstract: A global ocean general circulation model (OGCM) is used to investigate the mixed layer heat budget of the northern Indian Ocean (NIO). The model is validated against observations and shows fairly good agreement with mixed layer depth data in the NIO. The NIO has been separated into three subbasins: the western Arabian Sea (AS), the eastern AS, and the Bay of Bengal (BoB). This study reveals strong differences between the western and eastern AS heat budget, while the latter basin has similarities with the BoB. Interesting new results on seasonal time scales are shown. The penetration of solar heat flux needs to be taken into account for two reasons. First, an average of 28 W m 2 is lost beneath the mixed layer over the year. Second, the penetration of solar heat flux tends to reduce the effect of solar heat flux on the SST seasonal cycle in the AS because the seasons of strongest flux are also seasons with a thin mixed layer. This enhances the control of SST seasonal variability by latent heat flux. The impact of salinity on SST variability is demonstrated. Salinity stratification plays a clear role in maintaining a high winter SST in the BoB and eastern AS while not in the western AS. The presence of freshwater near the surface allows heat storage below the surface layer that can later be recovered by entrainment warming during winter cooling (with a winter contribution of 2.1°C in the BoB). On an interannual time scale, the eastern AS and BoB are strongly controlled by the winds through the latent heat flux anomalies. In the western AS, vertical processes, as well as horizontal advection, contribute significantly to SST interannual variability, and the wind is not the only factor controlling the heat flux forcing.

Molecular ecology of nifH genes and transcripts in the eastern Mediterranean Sea.

Abstract: The eastern Mediterranean Sea is one of the most extreme oligotrophic oceanic regions on earth in terms of nutrient concentrations and primary productivity. Nitrogen fixation has been suggested to contribute to the high N : P molar ratios of approximately 28:1 found in this region. Surprisingly, no molecular biological work has been performed in situ to assess whether N(2) fixation genes actually occur in the eastern Mediterranean Sea, or to determine which organisms are responsible for this process. In this study, we examined the presence and expression of nitrogenase genes (nifH) in the upper water layer of the eastern Mediterranean. Clone libraries constructed from both DNA and reverse-transcribed PCR-amplified mRNA were examined and compared. We observed different nifH genes from diverse microbial groups, such as Cyanobacteria, Proteobacteria and methanogenic Archaea. Interestingly, numerous phylotypes were observed in coastal stations at the DNA level but none were active. However, in far offshore stations, the phylotypes observed at the DNA level were the ones that were actually active. Our preliminary study revealed diverse diazotrophs that possess and express nifH genes, which may support N(2) fixation in the eastern Mediterranean Sea.

Reduced iron associated with secondary nitrite maxima in the Arabian Sea

Abstract: Dissolved iron and Fe(II) were measured in the oxygen minimum zone (OMZ) of the Arabian Sea in September 2004. The OMZ is a well-demarcated feature characterized by high rates of denitrification, and a deep nitrite maximum coinciding with oxygen levels below 1 μmol L -1 . This zone is significantly enriched in dissolved Fe relative to overlying and underlying waters and up to 50% of the dissolved Fe is present as Fe(II). The maxima in Fe(II) are at the same depth as the deep nitrite maxima, centered around 200-250 m. They coincide with a local maximum in total dissolved Fe, suggesting that Fe accumulates at this depth because of the greater solubility of Fe(II) over Fe(III). Fe(II) is thermodynamically unstable even at submicromolar oxygen levels, so active biological reduction is the most plausible source. To our knowledge, this is the first report of a potential link between Fe reduction, elevated dissolved Fe concentrations, and nitrite accumulation within an OMZ. Denitrification has a high Fe requirement associated with the metalloenzymes for nitrate and nitrite reduction, so in situ redox cycling of Fe has important implications for the nitrogen cycle.

Systemic bud induction and retinoic acid signaling underlie whole body regeneration in the urochordate Botrylloides leachi.

Abstract: Regeneration in adult chordates is confined to a few model cases and terminates in restoration of restricted tissues and organs. Here, we study the unique phenomenon of whole body regeneration (WBR) in the colonial urochordate Botrylloides leachi in which an entire adult zooid is restored from a miniscule blood vessel fragment. In contrast to all other documented cases, regeneration is induced systemically in blood vessels. Multiple buds appear simultaneously in newly established regeneration niches within vasculature fragments, stemming from composites of pluripotent blood cells and terminating in one functional zooid. We found that retinoic acid (RA) regulates diverse developmental aspects in WBR. The homologue of the RA receptor and a retinaldehyde dehydrogenase-related gene were expressed specifically in blood cells within regeneration niches and throughout bud development. The addition of RA inhibitors as well as RNA interference knockdown experiments resulted in WBR arrest and bud malformations. The administration of all-trans RA to blood vessel fragments resulted in doubly accelerated regeneration and multibud formation, leading to restored colonies with multiple zooids. The Botrylloides system differs from known regeneration model systems by several fundamental criteria, including epimorphosis without the formation of blastema and the induction of a “multifocal regeneration niche” system. This is also to our knowledge the first documented case of WBR from circulating blood cells that restores not only the soma, but also the germ line. This unique Botrylloides WBR process could serve as a new in vivo model system for regeneration, suggesting that RA signaling may have had ancestral roles in body restoration events.

Indian summer monsoon variability during the Holocene as recorded in sediments of the Arabian Sea: timing and implications

Abstract: Indian monsoon precipitation fluctuated significantly during the Holocene and a reliable reconstruction of the timing of the events and their implications is of great benefit to our understanding of the effect and response of low latitude climate systems to the forcing factors. We have carried out high-resolution terrigenous proxy studies on a laminated sediment core from the Oxygen Minimum Zone of the eastern Arabian Sea margin to reconstruct the summer monsoon-controlled precipitation changes during the Holocene. The temporal variation in the terrigenous proxy indicators of this core, in combination with other high-quality cores from the Arabian Sea, suggests several abrupt events in monsoon precipitation throughout the Holocene. The early Holocene monsoon intensification occurred in two abrupt steps at 9500 and 9100 years BP and weakened gradually thereafter, starting at 8500 years BP. A weakening in precipitation recorded at ∼7000 years BP, synchronous with similar conditions in India. One of the most significant weak monsoon periods recorded in our studies lies between 6000 and 5500 years BP. Spectral analysis of the precipitation records reveals statistically significant periodicities at 2200, 1350, 950, 750, 470, 320, 220, 156, 126, 113, 104 and 92 years. Most of these millennial-to-centennial cycles exist in various monsoon records as well as the tree ring Δ14C data and/or other solar proxy records. We suggest that throughout the Holocene, externally, small changes in solar activity controlled the Indian monsoon to a large extent, whereas internally, non-solar causes could have influenced the amplitude of decadal-to-centennial oscillations.

Assessing the use of a dietary probiotic/prebiotic as an enhancer of spinefoot rabbitfish Siganus rivulatus survival and growth

Abstract: The use of prebiotics and probiotics as feed supplements that improve efficiency of intestinal bacteria is becoming de rigueur in animal husbandry in many regions worldwide. We tested the effects of a commercial probiotic (Biogen � ) containing allicin, high unit hydrolytic enzyme, Bacillus subtilis spores and ginseng extracts on survival, growth, carcass composition and feed cost/benefit in rabbitfish Siganus rivulatus. Fifteen net cages (100 · 100 · 40 cm; L · W · H) were stocked with 10 juvenile rabbitfish (10.3 g per fish) each and placed in a large rectangular tank and offered feed at 4% body weight daily. Cages were offered one of five isonitrogenous and isocaloric diets containing 0, 1, 2, 3 and 4 g kg )1 probiotic at three replicates per treatment for 98 days. Fish in all cages were weighed at 2-week intervals and feed regimen was adjusted accordingly. Rabbitfish offered the control diet exhibited lower growth and feed utilization than all experimental treatments. There was no effect of probiotic inclusion level on survival but growth was better at all inclusion levels than in the control. No significant differences (P > 0.05) in growth were observed among fish groups fed various levels of the probiotic. Carcass composition was not affected by dietary probiotic inclusion. Ultimately, when all

The DDX3 subfamily of the DEAD box helicases: divergent roles as unveiled by studying different organisms and in vitro assays.

Abstract: DDX3 (or Ded1p), the highly conserved subfamily of the DEAD-box RNA helicase family (40 members in humans), plays important roles in RNA metabolism. DDX3X and DDX3Y, the two human paralogous genes of this subfamily of proteins, have orthologous candidates in a diverse range of eukaryotes, from yeast and plants to animals. While DDX3Y, which is essential for normal spermatogenesis, is translated only in the testes, DDX3X protein is ubiquitously expressed, involved in RNA transcription, RNA splicing, mRNA transport, translation initiation and cell cycle regulation. Studies of recent years have revealed that DDX3X participates in HIV and hepatitis C viral infections, and in hepatocellular carcinoma, a complication of hepatitis B and hepatitis C infections. In the urochordates (i.e., Botryllus schlosseri) and in diverse invertebrate phyla (represented by model organisms such as: Drosophila, Hydra, Planaria), DDX3 proteins (termed also PL10) are involved in developmental pathways, highly expressed in adult undifferentiated soma and germ cells and in some adult and embryo's differentiating tissues. As the mechanistic and functional knowledge of DDX3 proteins is limited, we suggest assembling the available data on DDX3 proteins, from all studied organisms and in vitro assays, depicting a unified mechanistic scheme for DDX3 proteins' functions. Understanding the diverse functions of DDX3 in multicellular organisms may be particularly important for effective strategies of drug design.

Atmospheric deposition and surface stratification as controls of contrasting chlorophyll abundance in the North Indian Ocean

Abstract: Intense upwelling during summer and convection in winter are believed to drive higher biological productivity in the Arabian Sea than in the Bay of Bengal. Although the Arabian Sea receives substantial atmospheric deposition of dust aerosols, its role in biological activity is unknown. We have analyzed chlorophyll-a (SeaWiFS), absorbing aerosol index (TOMS), surface winds (NCEP), and modeled dust deposition and SST (OI) data during two distinct seasons June-August (JJA, summer months) and October-December (OND, winter months) for the period 1997-2004. Climatologies of physicochemical properties have been developed from World Ocean Atlas 2001 (WOA01). Our results suggest that despite the strong vertical supply of nutrients in the western and central Arabian Sea regions, maximal chlorophyll-a was limited to the former region in both JJA and OND periods, suggesting the importance of atmospherically transported substances in determining chlorophyll abundance in the North Indian Ocean. Time-averages (1997-2004) revealed chlorophyll abundances in northwestern regions are larger than in other regions of the respective basins. The NW regions of the Arabian Sea and the Bay of Bengal have exhibited contrasting chlorophyll distribution patterns during El Nino years (1997-1998 and 2002-2003; positive SST anomalies); decreased and increased chlorophyll contents in respective regions. Following the passage of tropical cyclones, SeaWiFS records depicted large areas in the Arabian Sea to experience intensified chlorophyll production with strong wind speeds of 55-65 knots whereas its enhanced production occurred only in small patches even under the influence of Orissa Super Cyclone of October 1999 (wind speed up to 140 knots) due to strong stratification.

Offshore Frontal Part of the Makran Accretionary Prism: The Chamak Survey (Pakistan)

Abstract: The Makran accretionary prism developed in the north-western part of the Indian Ocean as a consequence of the subduction of the Arabian Sea since Late Cretaceous times. It extends from southern Iran to the Baluchistan region of Pakistan where it joins the Chaman-Ornach-Nal left-lateral strike-slip fault systems to the north and the Owen Fracture Zone-Murray Ridge transtensional (right-lateral) system to the south in a complex triple junction near the city of Karachi. In September to October of 2004, we surveyed most of the accretionary complex off Pakistan with R/V Marion Dufresne. We achieved a nearly continuous bathymetric mapping of the prism and the subduction trench from 62°30′E to the triple junction near 62°30′E together with nearly 1000 km of seismic reflection (13 lines) and we took 18 piston cores in different geological settings. One of the main results is that the frontal part of the Makran accretionary prism is less two-dimensional than previously expected. We interpret the along-strike tectonic variation as a consequence of lateral variations in sediment deposition as well as a consequence of the under-thrusting of a series of basement highs and finally of the vicinity to the triple junction.

Modeling the barrier-layer formation in the southeastern Arabian Sea

Abstract: The effect of salinity on the formation of the barrier layer (BL) in the southeastern Arabian Sea (SEAS) is investigated using an ocean general circulation model. In accordance with previous studies, the runoff distribution and the India–Sri Lanka passage have a strong impact on the realism of the salinity simulated in the area at seasonal time scales. The model simulates a BL pattern in fairly good agreement with available observations. Eulerian and Lagrangian approaches show that the BL is formed by two complementary processes, the arrival of low-salinity surface waters that are cooled en route to the SEAS and downwelling of waters mostly local to the SEAS in the subsurface layers. The surface waters are partly of Bay of Bengal origin and are partly from the SEAS, but are cooled east and south of Sri Lanka in the model. That the downwelled subsurface waters are warm and are not cooled leads to temperature inversions in the BL. The main forcing for this appears to be remotely forced planetary waves.

Growth performance and feed utilization of Nile tilapia Oreochromis niloticus (Linnaeus, 1758) and tilapia galilae Sarotherodon galilaeus (Linnaeus, 1758) fingerlings fed plant protein-based diets

Abstract: This study was designed to determine the effect of complete substitution of fish meal (FM) by three plant protein sources including extruded soybean meal (SBM), extruded full-fat soybean (FFSB) and corn gluten meal (CGM) on growth and feed utilization of Nile tilapia Oreochromis niloticus and tilapia galilae Sarothrodon galilaeus. Four isonitrogenous of crude protein (ca. 28.0%) and isocaloric (ca. 19 MJ kg−1) experimental diets were formulated. The control diet (diet 1) was prepared with FM as the main protein sources. Diets 2–4, each FM control diet, were completely substituted with SBM (diet 2), FFSB (diet 3) and CGM (diet 4). l-lysine and dl-methionine were added to plant protein diets to cover the nutritional requirements of tilapia. Each treatment was allocated to three net pens and fed for 17 weeks. Nile tilapia fed the control diet showed significantly higher (P≤0.05) values for final body weight (FBW), feed intake (FI), weight gain (WG) and specific growth rate (SGR), whereas fish fed the diet with CGM achieved the lowest values. Tilapia galilae fed SBM diet recorded the highest (P≤0.05) values for growth performance. Better feed conversion ratio (FCR) for both Oreochromis niloticus and Sarothrodon galilaeus was observed when fish were fed SBM diet, whereas the worse FCR was recorded for FFSB diet. Feed utilization parameters including protein productive value (PPV), fat retention (FR) and energy retention (ER) showed significant differences (P≤0.05) for both the species fed different dietary protein sources. The present results suggest that, for Nile tilapia, both SBM and FFSB supplemented with dl-methionine and l-lysine can completely replace dietary FM. Meanwhile, S. galilaeus fed SBM diet exhibited comparable growth and feed utilization with those fish fed a fish-meal-based diet.