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Dr. N. Saha



Name:  Dr. Nirmalendu Saha, Ph.D, FNASc., FZS

Designation:  Professor of Zoloogy

Specialization:  Biochemical Adaptation and Metabolic Regulation


Contact Information:

Biochemical Adaptation Laboratory
Department of Zoology,
North-Eastern Hill University
Shillong 793022, INDIA

Tel.: +91 364 272 2322 (work), +91 364 2550752 (home), +91-9436100836 (mobile)


Academic Qualifications:




B. Sc.


North-Eastern Hill University, Shillong

M. Sc.


North-Eastern Hill University, Shillong

Ph. D.


North-Eastern Hill University, Shillong




  • Fellow of National Academy of Sciences, India (F.N.A.Sc.)
  • Fellow of Zoological Society, Kolkata (F.Z.S.)
  • ISCA Young Scientists Award by the Indian Science Congress Association in the year 1990.
  • Young Scientist Best Speaker Prize and a gold medal by the Ichthyological Society of India for the year 1987.
  • National Merit Scholarship from Matriculation up to M.Sc.


  • DAAD Fellow (1st June 1 1991 30th  September 1993)
  • Senior DAAD Fellow (1st October to 31st December, 1997)
  • Visiting Scientist (BAT II) on invitation in the laboratory of Professor Dr. D. Häussinger, Germany (1st May, 2001 to 30th April 2002)
  • Senior DAAD Fellow (1st December, 2005 31st  January, 2006)


Memberships of academic societies, etc.:

  • Life Member of the National Academy of Sciences, Allahabad, India
  • Life Member of the Indian Science Congress Association, Kolkata
  • Life Member of the Indian Society of Biological Chemists
  • Life Member of the Indian Society of Comparative Animal Physiologists

Major areas of research:

  • Nitrogen metabolism in air-breathing teleosts with special reference to ornithine-urea cycle (OUC) and amino acid metabolism under environmental stresses.
  • Molecular mechanisms of regulation of ureogenesis and amino acid metabolism under environmental constraints in air-breathing catfishes.
  • Nitrogen and carbohydrate metabolism, oxidative stress and protein turnover with relation to cell volume changes in air-breathing catfishes.
  • Cell volume changes and early immediate gene expression in the hepatocytes of air-breathing catfishes.
  • Molecular characterization and regulation of expression of different nitric oxide synthase genes and the role of nitric oxide under environmental stresses in air-breathing teleosts.
  • Oxidative stress and antioxidant properties of air-breathing catfishes under environmental stresses.
  • Influence of nanoparticles on oxidative stress and antioxidant properties in air-breathing catfishes.


Number of M. Phil. /Ph. D. produced:

Ph. D. : 18



Dr. Jacqueline Dkhar    


Dr. Lipika Das


Dr. Supiya Dutta


Dr. Carina Goswami


Dr. Bidyadhar Das


Dr. Zaiba Y. Kharbuli


Dr. Arundhati Bhattacharjee


Dr. Shritapa Datta


Dr. Kuheli Biswas


Dr. Jamesteword Khongsngi


Dr. Lucy M. Jyrwa


Dr. Mahua G. Choudhury


Dr. Gitalee Bhuyan


Dr. Manash Das


Dr. Hnunlalliani


Dr. Bodhisattwa Banerjee


Dr. Priyanka Lal


Dr. Suman Kumari



M. Phil.: 1



Ms. Carina Goswami             



Number of Ph. D. students working for the degree: 6

  • Mr. Debaprasad Koner          
  • Ms. Rubaiya Hasan               
  • Mrs. Annu Kumari                
  • Mr. Elvis Khongmawloh       
  • Ms. Aquisha S. Lanong         
  • Mr. Revelbornstar Snaitang  


Major Research Projects completed/in progress:

  1. Role of amino acid metabolism in Indian air-breathing teleosts to survive under hyper-ammonia stress. GTZ, Germany (1996-2000).

  2. Purification and characterization of carbamyl phosphate synthetase(s), and expression of urea cycle enzymes during early developmental stages in an amphibious potential ureogenic teleost, Clarias batrachus. UGC, New Delhi (2001-2004)

  3. Culture of carps and air-breathing fishes in hilly region and   transfer of technology to rural population of Meghalaya. DBT, New Delhi (2002-2005)

  4. Physiological significance of occurrence/expression and tissue distribution of nitric oxide synthases, production of nitric oxide under environmental constraints and pathological conditions in the air-breathing catfish, Heteropneustes fossilis. DST, New Delhi (2006-2009)

  5. Molecular and functional characterization of nitric oxide synthases and production of nitric oxide under environmental constraints and pathological conditions in the air-breathing catfish, Clarias batrachus. UGC, New Delhi (2007-2010)

  6. Influence of hyper-ammonia stress on the expression of multiple glutamine synthetase genes, mRNAs for ornithine urea cycle enzymes and mitogen activated protein kinases in air-breathing catfish, Heteropneustes fossilis. DST, New Delhi (2010-2013)

  7. Molecular characterization in the expression of mRNAs for ornithine-urea cycle enzymes and enzyme proteins, multiple glutamine synthetase genes and signaling cascades under hyper-ammonia stress in the air-breathing walking catfish, Clarias batrachus. DBT Twining, New Delhi (2011-2015).

  8. Effects of high environmental ammonia on the expression of multiple glutamine synthetase genesmitogen-activated protein kinases and Hsp70 in the air-breathing mud eel, Monopterus cuchia. UGC, New Delhi.

  9. Possible upregulation of ornithine-urea cycle genes and involvement of MAPKs to adapt under hyper-ammonia stress in air-breathing catfish, Clarias batrachus. DST-SERB, New Delhi (2014-2017)

  10. Molecular adaptation during exposure to zinc oxide and titanium dioxide nanoparticles with special reference to oxidative stress, nitric oxide production, expression of heat shock proteins in air-breathing catfish, Clarias batrachus. DST-SERB, New Delhi (2018-2021)

  11. To elucidate the unique biochemical adaptational strategies that allow two air-breathing catfishes (Clarias batrachus and Heteropneustes fossilis) to survive in ammonia enriched toxic waste. NASF-ICAR (2018-2021)


Major findings in research

Prof. Saha has shown for the first time the unique presence of a functional ornithine-urea cycle (OUC) in two freshwater air-breathing catfish that are predominantly available in Indian subcontinent, such as Heteropneustes fossilis, Clarias batrachus (Saha and Ratha, 1987,1989; Saha et al., 1999), which otherwise is known to be non-functional or absent in typical fresh water teleosts. This unique finding by Prof. Saha has contradicted the earlier “gene deletion” hypothesis proposed by Brown and Cohen (1960) based on their findings of non-occurrence of functional OUC in fresh water teleosts, may be because of deletion of some genes required for OUC during their adaptive evolution in fresh water. In contrast, Prof. Saha and his group showed the existence of a functional OUC in air-breathing catfish, regulation of which depends on variable environmental constraints that they face regularly in natural habitats. For example, while living inside the mud-peat for months during the drought season under water restricted condition (Ratha et al. 1995; Saha et al., 2001), high concentration of ambient ammonia in stagnant water bodies due to evaporative water loss in summer (Saha and Ratha, 1990,1994; Saha and Das, 1999; Saha et al., 1995, 2003, 2007), and in alkaline condition (Saha et al., 2002), which compel them to switch over from ammoniotelic to ureotelic mode of nitrogen excretion by inducing the OUC enzyme activities. Although such unique adaptation was witnessed in amphibians, but not reported in any teleost species. In addition to this, Prof. Saha revealed existence of a functional OUC in non-hepatic tissues other than its usual presence in hepatic tissues, such as in kidney and muscle of these catfish as a special adaptation (Saha and Ratha, 1987, 1989; Saha et al., 1999), which is not found in higher vertebrates. Prof. Saha has also shown that these catfish have the capacity to accumulate very high concentration of ammonia while this is not so in mammals, where excess level of plasma ammonia may lead to coma and death.  Further, these catfish have the ability to convert the accumulated ammonia to glutamine and various non-essential amino acids very efficiently (Saha et al., 2000, 2002, 2007), as another unique adaptational strategy existing in these catfish. Another recent important contribution by Prof. Saha and his group is in relation to the occurrence of three glutamine synthetase (GS) genes expressed differentially in different tissues in catfish in contrast mammalian system, where the GS enzyme is encoded by only one gene, and all the three GS genes get induced specifically in different tissues under ammonia stress in high ambient ammonia (Banerjee et al. 2018).  His group has reported mitochondrial localization of both the isoforms of arginase (ARG 1 and 2), the last enzyme of the OUC, in C. batrachus liver, thereby suggesting that urea is exclusively synthetized inside the mitochondria of hepatic cells of catfish (Banerjee et al., 2017). This is again a unique observation in contrast to mammals, where urea is synthesised primarily in the cytosol of hepatic cells due to cytosolic localization of ARG, suggesting a regulatory role of mitochondrial urea synthesis in catfish.

Prof. Saha made a significant revelation regarding the presence of two types of carbamyol phosphate synthetase (CPS), the CPS I (ammonia- and N-acetyl-L-glutamate-dependent), which is normally present in higher vertebrates such as in mammals and amphibians, in addition to the presence of a typical fish-type CPS III (glutamine- and N-acetyl-L-glutamate dependent) activity in air-breathing catfish (Saha et al., 1997, 1999, 2007). This is again another novel contribution of showing the presence of both the OUC-related CPSes (CPS I and III) in a single vertebrate species, which was not observed together in any other vertebrate. It was suggested that glutamine- and N-acetyl glutamate-dependent CPS III, found in lower vertebrates, is the evolutionary precursor to ammonia- and N-acetyl-L glutamate-dependent CPS I of ureotelic mammalian and amphibian species (Mommsen and Walsh, 1989). Thus, the presence of both types of OUC-related CPS activities in these two catfish probably has evolutionary significance with relation to the evolution of OUC in vertebrates, in addition to their physiological significance of efficient conversion of toxic ammonia to urea via the OUC by involving both the isoforms of CPS under ammonia stress.

Prof. N. Saha and his group have also demonstrated the induction of nitric oxide (NO) synthesis by inducing the inducible nitric oxide synthase (NOS) gene under ammonia stress during exposure to high ambient ammonia and during mud-dwelling in air-breathing catfish (H. fossilis and C. batrachus) (Choudhury and Saha, 2012a,b; Kumati et al. 2018). He further suggested that the enhanced production of NO under ammonia stress, which is known to play diverse physiological functions in mammals under environmental stresses, is also playing a significant role in catfish in defending against the various ammonia-induced stressors as another adaptational strategy. His group has also recently demonstrated that enhanced production of endogenous NO can have antioxidant activity against the nanoparticle-induced oxidative stress in hepatocytes of air-breathing catfish (Koner et al. 2019).


Awards Received by Research Students:

Dr. Shritapa Datta:

  • Young Scientist Award by the Indian Science Congress Association, Kolkata (2004)
  • Swarna Jayanti Puroskar by the National Academy of Sciences, Allahabad (2007)

Dr. Kuheli Biswas:

  • Young Scientist Award by the Indian Science Congress Association, Kolkata (2007)

Dr. Mahua G. Choudhury:

  • President Dr. Shanakar Dayal Sharama Gold medal by the NEHU (2005)
  • Young Scientist Award by the Indian Science Congress Association, Kolkata (2010)
  • Swarna Jayanti Puroskar by the National Academy of Sciences, Allahabad (2012)
  • Dr. (Mrs.) Gouri Ganguly Memorial Award by the Indian Science Congress Association, Kolkata (2014)

Dr. Bodhisattwa Banerjee:

  • Young Scientist Award by the Indian Science Congress Association, Kolkata (2015)
  • NPDF by the SERB-DST for two years (2017-18)
  • Post-doctoral Fellowship to Israel for two years.


National: 16
International: 69




Updated by lakmen_zoology on Sep 09, 2019 11:21:20