by
V.R.P. Sinha
National Project Director
FAO/UNDP Projects
and
Head, Freshwater Aquaculture Research and
Training Centre (CIFRI), Dhauli
P.O. Kausalyagang
Via Bhubaneswar-751 002 (India)
When fish are cultivated, many species do not get the required environmental conditions which normally they require for propagation in the natural conditions and thus, though they are physiologically ready to spawn there, they do not spawn. Spawning habits differ considerably in different groups of fish. While certain fish are season-bound spawners and spawn in particular seasons such as spring, summer, rainy season and winter, others are non-season-bound ones and spawn round the year. Similarly, many of them spawn in confined waters, others in fluviatile conditions; some migrate from freshwater to the sea or from the sea to freshwater to spawn.
Most of the confined-water or freshly inundated area spawners lay sticky eggs and exhibit active parental care. Their eggs instead of settling down at the bottom and dying of inadequate oxygen get adhered with the help of sticky layer to objects, particularly green plants, where their oxygen demand is adequately met. Also, those fish exhibiting parental care normally lay the eggs on clumps to facilitate them to aerate properly and easily. Unlike these, those spawning in fluviatile conditions have floating, semi-floating or rolling eggs without any sticky layer, where the current of the water ensures adequate protection and oxygenation of the eggs. Besides adequate protection and oxygenation, proper food organisms need to be available for offspring. Inundated area or flooded river provides offspring the “richly laid” table of unicellular animals and rotifer especially developed because of submerged rotting dry grass and plants. Thus, the time, place, manner and habit of the spawning along with the number, size, physical and physiological properties of the laid eggs need to be in consonance with the controlled environment for successful induced breeding either by manipulating the environment or by hypophysation i.e., with the injection of fish pituitary extract.
Family Cyprinidae:
Aristichthys nobilis
Carassina auratus
Carassius carassius
Catla catla
Cirrhinus molitorella
Ctenopharyngodon idella
Cyprinus carpio
Hypophthalmichthys molitrix
Labeo calbasu
L. fimbriatus
L. gonius
L. rohita
Mylopharyngodon piceus
Ostoochilus hasselti
O. thomassi
Parabramis pekinensis
Puntius genionotus
Tinca tinca
Family Sacchobranchidae:
Heteropneustes fossilis
Family Clariidae:
Clarias batrachus
C. macrooephalus
Family Schilbeidae:
Pangasius larnaudi
P. pangasius
P. sutchi
Family Ophiocephalidae:
Channa marulius
C. striatus
C. punctatus
Family Cichlidae:
Etroplus suratensis
Helistoma temmincki
Tilapia hornorum
T. melanopleura
T. mossambica
T. zilli
Family Anabantidae:
Anabas testudineus
Osphronemus geramy
Trichogaster pectoralis
Family Megalopidae:
Megalops cyprinoides
Family Clupeidae:
Hilsa ilisha
Family Chanidae:
Chanos chanos
Family Anguillidae:
Anguilla bengallensis
A. japonica
Family Mugilidae:
Mugil cephalus
M. tade
M. dussumieri
Family Centropemidae:
Lates calcarifer
Family Polynemidae:
Eleutheronema tetradactylum
Polynemus paradiseus
Family Carangidae:
Seiola quingeradiata
S. purpurascens
Trachinotus carolinus
Family Serranidae:
Lateolabrax japonicus
Epinepholus sp.
Family Sparidae:
Crysophrys major
Mylio macrocephalus
Family Plecoglossidae:
Plecoglossus altivelis
Family Tetrodontidae:
Fugu rubripes
Of the listed fishes, attempts were made and are still being made to induce carp, catfish, mullet and milkfish to spawn in confined water through hypophysation technique with varying success. Many species have been successfully spawned and techniques have been perfected. However, the major reasons for getting erratic results of hypophysation both in freshwater and brackishwater appears to be the non-availability of ripe spawners. Also, the knowledge on the proper environmental conditions necessary for such spawning is very scanty.
However, most commonly cultivated fish could be conveniently grouped into three major groups on the basis of their amenability to induced spawning either by manipulating the environment or by hypophysation: (i) Species which can mature and spawn in ponds such as Tilapia mossambica (tilapia), Puntius gonionotus (tawes), Trichogaster pectoralis (sepat siam), Helostoma temmincki (kissing gourami), etc., (ii) Species which can mature and spawn in ponds when given suitable substratum/conditions even without hypophysation, examples, Cyprinus carpio, Osteochilus hasselti (nilem), Asiatic carps, etc. and (iii) Species which mature in ponds but do not ovulate there unless they are subjected to hypophysation. The examples are, Asian major carps, such as Catla catla, Labeo rohita, Ctenopharyngodon idella, etc.
To facilitate induced spawning different methods are used for the fish belonging to the above groups. Common carp which breeds almost throughout the year in Asia and Far-East is provided with weeds, grass or Kakabans as egg collector. In Indonesia, highly developed techniques for breeding of common carp have been evolved (Chaudhuri, 1967) which all involve providing suitable substratum to the parent stock for egg collection. These techniques are used in Thailand, Malaysia and Vietnam. In India and China submerged aquatic weeds like Ceratophyllum, Myriophyllum, Hydrilla, Najas and water hyacinth are used for the attachment of eggs. However, in Philippines, they are induced to spawn by hypophysation. While Carassius carassius, Puntius gonionotus and Puntius orphoides are supplied with running water in Indonesia to induce and accelerate spawning. The same techniques are adopted in Thailand and Malaysia. Different methods have been developed in Indonesia to induce spawning in the nilem, Osteochilus hasselti yet all methods provide a strong current of water to induce them to spawn. Similarly, Trichogaster pectoralis is also induced to spawn with the help of letting in fresh oxygenated water into ponds having submerged weed. Suitable aquatic plants or other such material for the construction of nests are necessary to induce spawning of gourami, Osphronemus goramy. In India, plants such as Typha are grown in the marginal areas of the ponds to facilitate gourami to build the nest. The same technique is used in Philippines and Ceylon. For spawning Helostoma timmincki, the spawning ponds are drained out and the bottom is dried up and then filled up with freshwater where paddy straw or floating aquatic weeds are spread on the surface of the water to provide shade to the eggs and protection to the larvae against rain and sun. For spawning Etroplus suratensis hard objects like wooden planks, slate, slabs, stones, bricks or bamboo poles are kept to facilitate eggs for attachment. Channa striatus, C. marulius, Clarias batrachus, Heteropneustes fossilis and Anabas testudineus spawn in confined water but methods have been developed in India for their controlled breeding through hypophysation.
In certain parts of India, the Indian carps are induced to spawn in special type of perennial and seasonal ponds or impoundment locally known as bundhs. These bundhs receive considerable quantities of rain water after a heavy shower from the extensive catchment area which induce fish to spawn without hypophysation. Thus, it appears that most of the freshwater fish are induced to spawn by providing proper substratum to lay their eggs and also that the freshwater supply to the pond has a conducive role, which will be elaborated in more detail later while discussing major carp induced spawning.
Spawning is the culmination of the reproductive cycle and thus the factors which influence reproductive maturity would indirectly or directly influence spawning for which spawners sexual maturity is the basic pre-requisite. Adequate and proper diet, suitable temperature/photoperiod, adequate living space and oxygen are well known factors which effect sexual maturity. Yet given all these, certain species, though sexually mature, do not spawn till proper environmental stimuli particularly temperature or photoperiod or rainfall are fulfilled.
Fish such as medaka, Cryzias latipes, the honmoroko, Gnathopegon caerulescous, etc. spawn during the long day season from spring to summer and it has been reported that these species could be matured and spawned by means of increasing the illuminated period (Yoshioka, 1963, 1966, 1970; Hibiya et al., 1972, 1973; Harrington, 1950, 1957). Whereas, salmonids which spawn in the autumn when the diurnal illumination is short, behave in the opposite way and were induced to spawn earlier by shortening the illuminated period (Corson, 1955; Nomura, 1962; Henderson, 1963). It is interesting to note that in case of Oryzias, light greatly influences spawning. They spawn before dawn and when day and night effects were artificially altered spawning occurred at the beginning of the artificially lit period after a few days. Yoshioka (1963) inhibited spawning in Oryzias by keeping them in darkness and then provided them with various amounts of artificial light. He found that in illumination greater than 5 lux all the fish which were ovulating spawned but in illumination less than one lux some spawned and some did not. Spawning was also induced by suddenly subjecting individuals which were already well lit to a very strong light (more than 5000 lux) and all ovulating individual spawned. This confirms that the occaional spawning of Cryzias during the day or in the evening is the result of changes in illumination. Yet, the fish will not mature at a temperature below 10°C, however, favourable the illumination conditions may be and so is the case with minnow which will not spawn below 7°C (Bullough, 1939). The gold fish will not spawn at any season unless the temperature is above 14°C. In contrast brook trout (Salvelinus fontinalis) raised under natural illumination showed no influence of temperature on maturation even with a temperature difference of 8.5°C to 16°C, maturation was effected only when there was artificial change between long-day and short-day period of illumination. Thus, it appears that both light and temperature are limiting factors in maturation and spawning in certain species but there are species in which temperature alone is the main factor in inducing maturation and illumination has no role of importance. Shehadeh (1976) remarks that since most physiological functions in poikilotherms are temperature dependent, photoperiodism seems to be temperature sensitive in a majority of the species examined. However, certain factors may become limiting in one situation while other factors may become limiting even for the same species in different agroclimatic conditions.
In case of major carps such as Catla catla, Labeo rohita etc. monsoon rain has a conducive effect on their breeding whether naturally breeding in wild or by hypophysation. Therefore, factors associated with rain such as temperature, turbidity, pH, O2 have been correlated to influence spawning of the carps but no critical factor was assigned which was responsible for triggering spawning in nature or in induced breeding. It has been observed that following injection of the pituitary extract fraction containing gonadotropin (Sinha, 1969), the gonad of the recipient spawner always became translucent and showed maximum percent of loss of weight after drying. Those fish which had commenced ovulating after getting the injection of fish pituitary gonadotropin lost 73.5% as compared to 63% in control. Males injected with this fraction showed the maximum percentage loss of weight of the semen after drying, much higher than those of control. The volume of semen increased to about twice the volume collected before the treatment. Major electrolytic ions such as sodium, potassium, calcium and magnesium and chloride in the blood and semen, showed that following injection of the pituitary extracts the cl level increases significantly in the blood of the female. As with the female, male serum cl significantly increased after the treatment but the level went down significantly in the seminal fluid differing from serum cl (Sinha, 1971) indicating the electrolytic concentration in the blood and dilution in the semen is because of the gonadal hydration which appears to be a pre-requisite for spawning of those physiologically ripe carps. In 1974, a hypothesis regarding spawning of carps suggested that during induced breeding gonadal hydration was achieved by the injection of the additional amount of exogenous pituitary material, whereas in natural spawning in riverine condition a sudden drop in the electrolytic level in the water by flood or heavy monsoon rain induced hydration of the fish as a whole and consequently the gonad, and those fish which were ripe in condition started spawning then in nature. It is common knowledge that when fish go from water of higher electrolytic level to lower level, for example, from sea water to freshwater, they gain water and thus the weight and reverse is true when they come from lower electrolytic level to higher level. In rivers and reservoirs, there is a marked increase of electrolytic level during mummer months and their level decreases suddenly after monsoon rain.
Further, the total water content of the ovary, the appearance of fluid in the space between the follicular cells, the loosening of the adhesion between the follicular cells and the egg and increase in diameter of egg suggest that these morphological changes accompanying ovulation are proceded by a remarkable absorption of water into the ovary and ovarian egg. Whether the condition prevailing in ponds during spawning season do favour such absorption of water or not needs investigation, especially because these carps do mature in ponds but do not spawn there. The water in these ponds is perhaps not that much diluted with rain or flood water as that of the rivers where they normally breed. In this context it is important to note that the males do spermiate in ponds but the female do not ovulate there. This may be because the sperm have no mechanical barrier to water movement unlike the chorion which may mechanically oppose or support the entry of ions and water to the egg for its final maturation (Sinha, 1980).
Wilhemi et al (1955) have shown that marked flexure and vibration of the body, which they called a ‘spawning reflex’, could be induced in Fundulus hetroclitus by the injection of highly purified vasopressin and oxytocin and by synthetic oxytocin. However, it is difficult to decide whether such reflex is the true spawning reflex, since the experiments were not planned to show the emittance of the genital products following the reflex. Egami (1959) and Ishii (1961) claimed that neurohypophysial hormones were effective in inducing spawning. However, Sinha (1971) found negative correlation between the presence of isotocin/arginine vasotocin and spawning.
It is sometimes said that a two-component control system with two gonadotropins may be needed: one for cogenesis and vitellogenesis and the other for ovulation. Thus, in case of these carps which do not normally ovulate in ponds, though achieving gonadal development up to fourth stage, it may be argued that they may not contain the other gonadotropin which is responsible for ovulation. Yet, it is interesting to note that pituitary of donor carps inhabiting ponds is effective on the recipient, which also inhabit the ponds. Thus, if donor pituitary is lacking the ovulating gonadotropin it would not have been effective in inducing spawning of others. In this regard, it is essential to point it out that the same fraction containing pituitary gonadotropin (Sinha, 1969) induced courtship behaviour as well as ovulation of viable eggs in the carps (Sinha, 1971) and also maintained and initiated all the reproductive process in the hypophysectomised female catfish indicating that some gonadotropin does both the functions in the carps (Sundararaj, et al., 1972).
Further investigations indicated that qualitatively there appears to be no difference in the gonadotropin of a free spawner like common carp and refractory species like Indian major carp or Chinese carps. However, when quantitatively assessed it has been found out that the gonadotropin content of the pituitary gland of common carp and Puntius gonionotus is considerably more than that in the pituitary glands of the other carps which do not breed in confined water presumably due to reduced accumulation of gonadotropin in the pituitary gland and therefore the additional amount of exogenous pituitary material is needed to induce those refractory fishes to spawn in confined water. The reason for reduced accumulation of the gonadotropin needs thorough endocrinological investigation in terms of ecological parameters of the environment and the reproductive biology of the fish. However, researches are actively going on to induce spawning with the intervention at the hypothalamic-pituitary interface through the administration of LH-RH. The introduction of the synthetic LH-RH (luteinizing hormone-releasing hormone) for ovulation which causes an elevated plasma level of gonadotropin hormone in the common carp, Cyprinus caroio (Breton and Weill, 1973) appears to be promising. Its use along with fish pituitary extract is giving excellent results in carp breeding in China.
Many have started experimenting ovulation with sex steroids with conflicting results. However, it can be fairly presumed that with the present knowledge of the spawning of the fish much better results of induced spawning of cultivable species could be achieved if ripe parent stock is available and they are subjected to hypophysation with simulation of natural condition for the spawning.
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