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In water, the determination of acid or base is related to quantity of hydrogen ions (H+). The scale for measuring the degree of acidity is called the pH scale, which ranges from 1 to 14. A value of 7 is considered as neutral, a value below 7 is acidic and above 7 is base. The acceptable range for fish culture is normally between pH 6.5- 9.0. Very high (above 9.5) or very low (less than 4.5) these ranges are unfavorable condition for most aquatic organism. Water quality consider is key for successful of aquaculture. In aquaculture system, various physico-chemical parameters are influencing significant role in their fish production, although pH is the main parameter to affect the water quality. Both extreme and lower pH can affect the physiological function in reproduction and growth of fish, even cause mass mortality in fish culture. The fertilization of most fish species is unsuccessful at water pH lower than 4.0 (Yang et al., 2011).
Most teleost fish species are oviparous, producing yolk containing eggs, although viviparity, with embryos developing within the female reproductive system.
There are three main types of ovarian development have been noted for fish. (1) synchronous, where all oocytes develop and ovulate at the same time, (2) group-synchronous, where at least two populations of oocytes can be recognized in the ovary throughout the reproductive season (i.e. vitellogenic and maturing), and (3) asynchronous, where oocytes of all stage of development are present without a dominant population. Asynchronous ovulators” or batch spawners, eggs are recruited into maturation and ovulation from the population of yolked oocytes in several batches during the spawning season (Wallace and Selman, 1981).
The swelling of the egg is completed, the two parts of the egg kernel have become well-formed and are easily distinguishable by form and colour. The animal pole rises as a small hillock on the yolk mass and develops a dark yellow colour. After a short time, the duration of which depends on the temperature of the water, the cleavage of the animal pole starts and the one-cell “hillock”, successively becomes 2, 4, 8, 16, and 32 celled. At this stage it looks like a mulberry (morus in Latin) and is, hence, termed the morula stage and cells are undergo further subdivision and its yields a many-celled “blastoderm”, which to start with has only one layer of cells. It gradually acquires several layers of cells. Each of these cells is termed the “blastomere”. At the morula stage the developing embryo is very sensitive to shaking and the cells may become torn off from the surface, resulting in the death of the embryo. A space, termed the segmentation cavity, appears later on between the yolk and the cell mass. At this stage, the embryo is called the blastula.
The cells of the blastoderm initially arrange themselves on top of the yolk in the form of a cup. As cell division progresses, the cells start covering the yolk resulting finally in enclosing the yolk mass completely, leaving at one end only a small opening, the blastopore. Later, this also completely closes. This is the transition point to the embryonic development stage from the initial germ development stage.
Pollution of aquatic environment resulting from acid precipitation and increase the environment problem to the aquatic organism. Low pH levels accelerate the release of metals from rocks or sediments in the stream. These metals can affect a fish's metabolism and the fish's ability to take water, in lower pH range can increase the heavy metal toxicity in certain water bodies. The low pH values (4.5 to 5.0) are suffer the fishes significantly declined their egg production in reduced (ex. flagfish and jordanella floridae, common carp). Generally, egg fertilization after few hours it will undergo several changes. The chorion hardnening and plasma membrane from resistant barrier to protect the developing embryo from external medium. The chorion is at first freely permeable to water and various molecules and later resistant to osmosis and diffusion. Soon egg laying, only the perivitelline space is penetrable by water. As damage to the osmotic activity of perivitelline colloids reduced water uptake of eggs cultivated at low pH values. The eggs are susceptible to acid exposure immediately after fertilization until the membrane have hardened due to this very low hatching percentage of egg laid, fertilized in low pH level (Lee and Gerking, 1979). The oogenesis is more sensitive to acidity condition rather than alkaline condition. And also fish larvae, immature insects are more sensitive to pH level 5 and may die in this low pH (ex. Cyprinus carpio larvae died after nine days in water with pH lower than 5.0).The harmful effects of an acidic pH may be easily observed in the egg membranes through the emergence of bubbles that stick to them. This makes the eggs float on the surface of the incubator (Zaniboni-Filho, 2000). In acidic condition lake female fishes possess the low serum calcium concentration in the ovarian maturation period. George Lake fishes are disappeared due to low pH condition and they stopped reproduction (Beamish at al., 1975). In increasing hydrogen ion concentration is relation to increase the heavy metal toxicity in water it could lead to cease the many fish spawning. The low pH values are affecting the egg in following ways.
Lethal pH level for eggs and larvae of different teleost species (source; Oyen et al., 1991)
*The available study on lethal pH level for egg and larvae are limited for Indian cultivable freshwaters fish species. A specific detailed scientific studies are required further for few more species.
Approach pH level for egg and larvae of cultivable freshwater fish species in India;
High pH levels (9-14) can harm fish by denaturing cellular membranes. Changes in pH can also affect aquatic life indirectly by altering other aspects of water chemistry. At high alkaline condition NH4 is converted into toxic from NH3 and also It will strip a fish of its slime coat and high pH level ‘chaps’ the skin of fish because of its alkalinity. The chronic exposure to pH value above 10 is harmful to all species. A pH range of 6.5 to 9.0 provides adequate protection for the life of freshwater fish and bottom-dwelling macro invertebrates. Beyond this range, its cause severe physiological damage to fishes. Extreme pH can kill adult fish and invertebrate life directly and can also damage developing juvenile fish. When the pH of freshwater becomes highly alkaline (e.g. 9.6), the effects on fish may include: death, damage to outer surfaces like gills, eyes, and skin and an inability to dispose of metabolic wastes. High pH may also increase the toxicity of other substances. The physiological effects on aquatic life induced by high pH (>9) have been studied less than those at low pH. This is likely because high pH waters are less common. The effect of pH is related to age and developmental stage and larval stages were observed to be most sensitive to pH changes
As being several Water quality parameters is playing significant role in the many aquatic life. Among these pH is also consider as one of the most important parameters to many fishes, in their early life stages; although pH is the measurement of the acidity, alkalinity of the water or soil. The lower and higher pH condition fish growth reduced and reproduction failure occur and most of the fishes do not survive in the below pH 4 and above pH 11 for long periods. The pH values are affecting the fishes including oogenesis, exchange of ions with water and respiration, and also fertilization and hatching of many fish species. The hatching period of salmonids, carp, flag fish, eastern catfish are influenced by pH. As serious chronic effect is increased acidity surface water to hinder with fish reproductive cycle. The low pH level is causing the reduction of calcium level in female fish and they cannot produce egg or eggs fail to pass from the ovaries or fertilized, the developed larval become abnormal condition. There several studies are available about effect of low pH of fish growth, survival, and reproduction than high pH. Suitable and widely accepted pH value for fish culture is 6.5 to 8.5. In the above viewed content, water pH range is having significant role in production of early life stage of fishes and their production.