The following points highlight the top ten roles of biotechnology in aquaculture. Some of the roles are: 1. Nutrition 2. Feeding Stimuli and Chemical Signal 3. Reduce the In-Pond Chemical Oxygen Demand 4. Administration of Mammalian Hormones 5. Cryopreservation 6. Use of Allomones and Pheromones 7. Genetic Manipulation 8. Hormonal Manipulation for Sex Control and Others.
Role # 1. Nutrition:
Indian aquaculture industry lags behind in the science of nutrition. A good approach would be to improve the quality and utilisation of various agricultural and industrial by-products for efficiency.
Various foodstuffs having potential values as fish feed ingredients have not been nutritionally utilised as they contain toxic or anti-nutritional factors. The need of biotechnology is to develop new varieties of foodstuff with totally free or low content of such intoxicants.
Other developments of improved feeds are:
ADVERTISEMENTS:
(1) Development of food additives, such as anabolic steroids and thyroid hormones, have resulted in increased growth of salmonid fishes.
(2) Development of new artificial diets, such as micro-encapsulations for filter-feeders (oysters and mussels).
(3) Improved culture of single-celled feed organisms (algae, yeast, bacteria).
Role # 2. Feeding Stimuli and Chemical Signal:
To obtain the full sequence of feeding behaviour from initial recognition of feeding ‘strike’ to ingestion of food particles, it is necessary to identify the feeding stimuli or chemical signal. It is thus required to genetically design or engineer the bacterial strain with characteristics of having better cellulose degradation capacity.
Role # 3. Reduce the In-Pond Chemical Oxygen Demand:
ADVERTISEMENTS:
Microbial processing of livestock manure through anaerobic digestion in biogas plants reduces the in-pond COD.
It also improves the fertilisation quality of the inputs, Biotechnology has attained great significance in aquaculture development by increasing the nitrogen fixation levels in ponds through bio-fertilisation with blue-green algae (azolla) and green-manuring and through genetic manipulation of bacteria to improve their nitrogen fixing capacity. This has definitely increased fish production.
Role # 4. Administration of Mammalian Hormones:
Mammalian gonadotropic hormones have been used extensively for spawning of carps and catfishes. Hormonal manipulation of sex is being practised to control unwanted reproduction in prolific breeders such as common carp and Tilapia. Administration of mammalian growth hormones through feed or injection has enhanced fish growth. Manipulated monosex population improves nutritive value of fish flesh and growth.
Role # 5. Cryopreservation:
Cryopreservation refers to preservation of gametes and embryo generally at below freezing temperature for ready availability of genetic material for breeding and research purposes. Cryopreservation of milt has been successfully developed for several fishes.
ADVERTISEMENTS:
It is essential since the males of some fish species mature earlier than the females and there would be dearth of oozing males when fully mature female fishes would be available. Cryopreservation of zygotes and embryos have facilitated large scale fish seed production programme.
Role # 6. Use of Allomones and Pheromones:
In large scale induced breeding, use of allomones and pheromones is of great significance. Under biotechnological programme it is necessary to study the role of pheromones in alarm and social behaviour, species and sex recognition, sex behaviour and territorial and space recognition.
Role # 7. Genetic Manipulation:
Change in genetic make-up of any organism by application of improved bio-techniques is referred to as genetic manipulation. Fishes, generally, can tolerate a wide range of genetic manipulation than terrestrial farm animals.
(a) Chromosome Manipulation:
Through chromosome manipulation fish stock can be improved for breeding and culture by way of gynogenesis, androgenesis and polyploidy.
(i) Gynogenesis (all Maternal Inheritance):
Gynogenesis in fishes can be induced by stimulating parthenogenetic development of fish eggs by artificially inactivated spermatozoa. Through X-ray or UN-rays, the genetic contents (DNA) in spermatozoa can be destroyed.
With such spermatozoon fertilisation would occur without any contribution from them. The diploid parthenogenetic individuals would give rise to offsprins that would be females having maternal inheritance only Ex. Grass carp, Salmon, Rainbow trout, etc.
(ii) Androgenesis (all Paternal Inheritence):
ADVERTISEMENTS:
Similarly with X-rays or UN-rays the genome of ovums can be destroyed and fertilisation with normal spermatozoon would result in homogametic males having paternal inheritance only. Ex. Common carp.
(iii) Polyploidy:
Polyploidy (individuals having extra sets of chromosomes) can be achieved by subjecting fertilised eggs to heat, cold, pressure or chemical shocks. Polyploidy produces
(1) Sterile individuals,
(2) Enhanced growth and survival,
(3) Improved quality of flesh in some fishes,
(4) More viable and ideal for producing new hybrids.
(b) Gene Transfer or Transgenesis:
Transgene- sis results in formation of ‘Transgennic fish’. The techniques involved is through micro-injection and electroporation, genes are introduced into one-celled embryo or oocyte.
The potentialities of transgenesis are:
(1) Tolerance to physical factors. Ex. tolerance to cold using antifreeze gene.
(2) To accelerate growth by using growth hormone genes.
(3) Efficient use of food by fishes through manipulation of biochemical pathways.
(4) To increase disease resistance by using specific disease resistance genes (Ex. T-cell receptor, immunoglobulin, lymphokines, etc.).
(5) Behavioural modification (maturation, reproduction, sex control, etc.) by regulation of endocrine function.
(c) Application of Cell Culture Biotechnology to Marine Macro-Algae:
Seaweeds can be easily genetically engineered. In many maritime countries, tons of seaweeds are produced through mariculture, which are used as human food (green seaweeds) and for commercial production of phyco-colloids (agar, algins, carrageenas, etc.) for industrial purposes.
Role # 8. Hormonal Manipulation for Sex Control:
Sex hormones (steroids) are used to produce monosex for culture of tilapia in particular. Tilapia being a prolific breeder, creates problem in pond culture as it results in overcrowding with small size fishes and thus, in decreased production. Therefore, monosex culture controls reproduction and also helps in increased production.
To obtain only males by sex reversal method, the early fry of tilapia are fed with androgen 17-a methyl testosterone for induction of sex reversal from genetic females to phenotypic males. Similarly, in species where females are bigger and grow faster than males, only females can be produced for monosex culture by feeding fry with estrogen 17b-Estradiol benzoate or diethyl stibestrol.
Role # 9. Fish Disease Management:
Fish diseases can be controlled through development of biotechnologically produced vaccines. Vaccines against vibriosis and furunculosis have been developed and are available in the market. However, they are for limited fish species. There is an increased demand to use biotechnology for developing vaccines against bacterial, viral and other diseases affecting several commercially important culturable fish species.
Role # 10. Current Breakthrough and Essentials for Future Research:
Technological advancement has led to freshwater and marine pearl culture product development such as chitin, chitosan, etc. Further studies for even more efficient and large scale production technologies is essential.
Attention should be drawn towards genetic improvement of fish stock through selection and genetic engineering, ex-situ conservation methodologies, gene banking both with live and gamete level approaches, which would subsequently lead to future research. Social impact of fisheries and aquaculture development has to be studied and the need is to develop parameters to undertake Social Impact Assessment (SIA).
Thus, for the development of biotechnology it is urgently required to upgrade laboratory facilities and attract young blood for research and training. It should be noted that water resources in the country are not exclusively available for aquaculture as there is excessive pressure on their use from several other sectors.
Therefore, any further growth in aquaculture for quantum jump would have to be vertical and technology based. The transfer of technology from the laboratory to the field has had its own causalities.
Today only about 30% of the proven technology available in various fields of aquaculture has been manifested in the field. There is thus, urgent need to narrow the gap between the results of research and those in the farmers field.