Hatchery Management

Hatchery – a facility where eggs are hatched under artificial conditions

Facts:20,000 - total number of fish species in the world 2,200 - total number of fish species in the Philippines of which, 100 species are commercially impt.

Fish Production Methods

1. Capture

2. Culture

Criteria for Candidate Species for Fish Culture(i)It must withstand the climate of the region in which it will be raised. Thus, the rearing of coldwater fish like salmonids and trout is limited to temperate regions or mountain areas of tropical countries because they can not tolerate warm water with its low oxygen content.

(ii) Its rate of growth must be sufficiently high.

Small species, even if they reproduce well in ponds and accept formulated diets, are not the most suitable for rearing.

Also, the best culture species are those which are low in the food chain, e.g., plankton feeders, herbivores, and detritivores. Their culture is also least expensive, even on an intensive scale, because they do not need to be given diets which have a high content of animal protein.

(iii) It must be able to reproduce successfully under culture conditions.

Species for culture should be able to reproduce in captivity/confinement without needing special conditions that have to be fulfilled, and which give high returns on eggs and fry.

(iv) It must accept and thrive on abundant and cheap artificial food.

Culture species which feed on cheap artificial feeds and give low feed conversion ratios (FCRs), also tend to give very good production rates, thus bringing in better financial returns.

(v) It must be acceptable to the consumer.

Even if all the foregoing criteria are met by a candidate species, it is not worth culturing if there is no market for it. It is possible, though, to promote acceptability of or encourage consumption of a particular species to ensure that it will eventually sell in the market. (This was the situation with tilapia in the Philippines prior to the introduction of the bigger-sized, lighter coloured S. niloticus in the early 1970s.)

(vi) It should support a high population density in ponds.

Social and gregarious species which can grow well to marketable size even under high density conditions in ponds or tanks are preferable to those which can be grown together in dense numbers only up to a certain age beyond which they eat each other (e.g., pike).

(vii) It must be disease-resistant.

Reared fish must be resistant to disease and accept handling and transport without much difficulty.Tilapia for example is an ideal species for culture because of its high resistance to disease even in highly intensive culture systems.

initial and basic requirement of fish culture:

production of young fish for stocking

Fish culture today is hardly imaginable without the artificial or semi-artificial mass propagation of fish seeds of cultured fish species. The need for production of quality fish seed for stocking the artificial ponds and natural water bodies has been steadily increasing.

Artificial propagation methods constitute the only practicable means of providing enough quality seed

NATURAL PROPAGATION OF FINFISH

Significance of Propagation

to survive and flourish and add a large number of offspring to the population.

Biology of Propagation

The propagation habit is the most vital adaptation of the fish to its environment with respect to survival.

For successful propagation, the place where eggs are released should have optimal conditions with respect to oxygen, temperature, food, etc. and should be almost free of enemies. Those fishes unable to find such conditions have gradually been eliminated.

The nature of the propagation habit of any fish is determined by:

1.the age or time of sexual maturity2.the season of propagation, 3.the place of propagation, and4. the extent of parental care

Age of sexual maturity

Some fishes, such as Tilapia spp., become sexually mature within a few months, while others may take as long as a few years.

Sexual maturity depends on: a. Climate - Sexual maturity is delayed in cold climates, while it is accelerated in warmer environments. b. Type of spawner – whether multiple spawners or season-bound spawners

Season of propagation

- a slight change in temperature, oxygen, and other parameters greatly affect cold-blooded animals a. Multiple spawners –matures earlier than season-bound spawners

b.Season-bound spawners

Place of propagation

Freshwater fishes are known to spawn in three different types of sites:

(1) confined waters

(2) flowing waters

(3) inundated terrains.

Parental care

- is a very important adaptation among fish for ensuring the survival of their offspring where parent fish look after their offspring during their most critical stage of life when they are defenseless and very sensitive.

This is actually the “hereditary foresight” of the females to provide more yolk for the embryo to sustain life for a long time or to place the eggs on such sites where the optimum environmental conditions are met (or are most probably met) and beyond the reach of enemies. Some fish have in their eggs a poisonous substance which keeps predators away.3.2.4.2 Active parental care. In active parental care, either one or both of the parents take an active part in caring for and defending their eggs, larvae, and sometimes the fry as well. This includes the selection and preparation of a suitable place for depositing the eggs, selection of a good substrate to which the eggs can adhere, collection of nest making materials, and preparation of the nest (Figure 3).The so-called “nest cleaners” have the most primitive type of “nest”, consisting of just the bushy roots of plants which are only cleaned by the fish. There is no actual collection of nest building materials involved nor actual nest building. On the other hand, the “nest builders” collect pebbles, leaves, roots, etc. and build their nest (e.g., giant gourami). Some of the gouramis prepare their nest out of objects which are cemented together with a foamy sticky substance. The “foam nest builders” make their nest out of foam, which being unpalatable, protects the eggs hidden in the foamy mass (e.g. Trichogaster spp.). Then, there are the mouth breeding cichlids (Tilapia leucosticta, T. galilea, T. macrochir, T. nilotica, T. variabilis, T. macrocephala, Haplochromis spp., Astatoreochromis alluandi, Serranochromis spp., Petenia spp., etc.). These fishes take the eggs into their mouth, and keep them there until they hatch. Among the tilapias, the female incubates the eggs in the case of T. leucosticta, T. macrochir, T. nilotica, and T. variabilis; the male in the case of T. macrocephala and both the sexes in the case of T. galilea. In the case of the pearlspot, the eggs are attached to the underside of submerged objects, where they are fertilized and remain until hatching. The newly hatched larvae are taken to nearby shallow pits prepared by the male and are shifted from one pit to another about once a day. Later, the fry are guarded by the female. The non-mouth-breeding tilapias (T. zillii, T. melanopleura, and T. sparmanii) deposit their eggs on stones or other substrata and zealously guard the eggs and larvae.Apart from depositing the eggs in a safe and congenial place, parental care extends further to the aerating and protection of eggs, and in some cases the protection of the spawn and fry as well. Aeration is done by one of the parents by producing a continuous water current over the eggs by means of its fins, the parent fish guarding its eggs or larvae from small enemies and larger predators. It also cleans the developing eggs and removes the unfertilized ones.In general, the following conclusions can be drawn with respect to the influence of parental care on the number of eggs produced:fish with passive parental care produce more eggs than those exerting active parental care;fishes with active parental care produce far fewer eggs than those which do not exhibit parental care, andfishes that abandon their eggs after laying them produce more eggs compared to those not abandoning their eggs.The number of eggs produced per kg of body weight depends on the size of eggs. Fish producing very small eggs (0.3–0.5 mm in diameter) produce 500 000–1 000 000 eggs per kg of body weight, while those with eggs of medium size (0.8–1.1 mm) produce only 100 000–300 000 eggs per kg of body weight. Those with larger sized eggs, 1.5–2.5 mm, produce only about 5 000–50 000 eggs per kg of body weight.In culturing fishes with well developed parental care, the fish culturist need not bother about artificial propagation. However, these naturally propagating fish, such as tilapias, often pose a major problem by overpopulating the pond. Therefore, the fish culturist has to take certain measures to prevent excessive propagation. Monosex culture or culturing them with some predator species is often practised.Hence, such fishes (tilapias and others) have been excluded from the scope of this manual.

Types of Parental Care

Passive - This is actually the “hereditary foresight” of the females to provide more yolk for the embryo to sustain life for a long time or to place the eggs on such sites where the optimum environmental conditions are met and beyond the reach of enemies. Some fish have in their eggs a poisonous substance which keeps predators away. 

a.Active

b. Active

- either one or both of the parents take an active part in caring for and defending their eggs, larvae, and sometimes the fry as well. This includes the selection and preparation of a suitable place for depositing the eggs, selection of a good substrate to which the eggs can adhere, collection of nest making materials, and preparation of the nest

Development of the Sexual Products

1.Development of eggs

Stage I: The primitive egg cells (ovogonium or archovogonium) are very small, their size being hardly bigger than that of other cells (8–12 microns). They multiply by normal mitosis.

Stage II: The egg cells grow to a size of 12–20 microns, and a follicle begins forming around each egg cell. The follicle, whose function is to nurture and protect the developing egg, eventually becomes a double layer of cells.

Stage III: During this stage, the egg cell grows significantly larger to attain a size of 40–200 microns and becomes enclosed by the follicle..

These first three stages mark the period prior to the accumulation of nutrients in the developing eggs.

Stage IV: During this stage the production and accumulation of the yolk begins; this is a process known as vitellogenesis. The egg continues to grow to a size of 200–350 microns with the accumulation of drops of lipoid materials in its cytoplasm.

Stage V: This marks the second phase of vitellogenesis. The cytoplasm is now full of lipoid drops and yolk production begins. The egg size reaches 350–500 microns.

Stage VI: This is the third phase of vitellogenesis, during which the yolk plates push the lipoid drops toward the edge of the cell where two rings begin forming. The nucleoli, which take part in protein synthesis and the accumulation of nutrients are seen adhering to the membrane of the nucleus. The size of the egg is now 600–900 microns.

Stage VII: The process of vitellogenesis is completed during this stage and the egg attains a size of 900–1 000 microns. When the yolk accumulation ends, the nucleoli withdraw into the centre of the nucleus. The micropyle (a small opening on the egg shell) develops during this stage.

Stages IV, V, VI, and VII are the stages of vitellogenesis, when yolk is synthesized and accumulated in the egg cell. The egg is now materially ready. To reach this stage of development, the female fish needs a lot of protein in its food and a favourable temperature range

Further development of the eggs toward ovulation (final ripening) is regulated by gonadotropin hormones, which are formed and stored in the pituitary gland or hypophysis. Some hormones of the hypophysis, such as FSH (follicle stimulating hormone) and LH (luteinizing hormone), are continuously produced and secreted into the blood stream.

On the other hand, the steroid type of hormones (oestrogens) secreted by the capsule (theca) of the follicle “inform” the brain about the stage of egg development.

On the completion of stage VII, the egg may remain as such for several months without any change, and this forms the “dormant” or “resting” phase.

This resting or dormant phase will either end in ovulation if favourable conditions occur, or in follicular putrefaction and resorption in the absence of such conditions.

When the environment changes for the better, the fish starts gathering, through its sense organs, all the necessary information about environmental conditions; e.g., temperature, suitable place for spawning, water current, floods, presence of fish of the opposite sex, etc.

This sensory information accumulates in the hypothalamus of the brain and when a certain threshold level is reached the hypothalamus gives an order through a hormone (gonadotropin-releasing-horwone, GRH) to the hypophysis to release gonadotropins into the blood system. The gonadotropins, thus released, reach the gonad and trigger the preovulation process and final ovulation.

The first effect of gonadotropins on the egg is the movement of its nucleus toward the micropyle. This is followed by what is termed as “hydration”, wherein the eggs absorb water. All these are completed during the preovulation stage.

After preovulation, the membrane of the nucleus disappears, the chromosomes become visible, and the first cell division of meiosis occurs (during which the total number of chromosomes is reduced to half). At the same time, the follicle keeping the egg fixed on to the wall of the ovary gets dissolved by enzymes and the “ripe for fertilization” egg falls into the cavity of the ovary.

The second cell division of meiosis normally takes place in the presence of the sperm, which intrudes into the nucleus of the egg through the micropyle. Therefore, the presence of the male pronucleus is necessary for the development of the female pronucleus.

OOGONIAL PROLIFERATION PHASE

VITELLOGENESIS PHASE

RESTING OR DORMANT PHASE OVULATION RESORPTION/

PUTREFACTION

SPAWNING

What happens during ovulation?

1.Migration of the nucleus to the periphery of the egg near the micropyle

2.Hydration

3. Breaking/rupture of the follicle

4. First phase of meiosis(cell division of meiosis in which the number of chromosomes is reduced to one half)

2. Development of Sperm

The process of development of sperm is far less complicated than that of eggs.

Characteristics of the Sperm

oThe sperm are motionless in the testis but become motile when they come in contact with water.

oThe motile period of the sperm is very short and depends on the temperature of the water.

oThe sperm of warmwater fishes move actively by their filamentous tail for only about half or one minute.

o The fish sperm are very small, their estimated number in one cubic centimetre of milt being about 10 000–20 000 million depending on the denseness of the milt.

Fertilization and Fertilized Egg

oThe eggs that have fallen into the cavity of the ovary do not have definite shape.

oThe egg shell is soft and tightly surrounds the cell “kernel”, which includes the nucleus and the mass of yolk.

oWhen the ripe egg falls into the water it assumes a round shape and within a short time begins to swell.

oThe water penetrates between the shell and kernel of the egg and thus the perivitelline space develops.

oThe micropyle closes within a minute, after which no sperm can enter the egg. The swelling usually lasts for about one-two hours. The egg then takes its final form and becomes water-hardened. The swelling, however, does not alter the size of the kernel.

oThe fertilized fish eggs can be of different types. However, for practical purposes, two principal categories can be distinguished:

1.non-adhesive

2.adhesive

Non-adhesive eggs

Types:1.buoyant eggs - specific weight slightly less than that of water

2. floating eggs - specific weight weight is slightly higher than that of water

3. semi-floating eggs- specific weight is higher than that of water

4. rolling eggs - specific weight is higher than that of water

What determines the specific weight of eggs?

Answer:

The specific weight of eggs is determined by the:a.size of the perivitelline space

b.the specific weight of the kernel-affected by presence or absence of oil droplets

Adhesive eggs

oThese eggs have an adhesive layer on their shell, which becomes activated when the egg comes into contact with water.

oThe adhesive layer sticks the eggs to some objects or to each other.

oTwo types of attachment can be distinguished:

1. eggs sticking to objects

2. eggs sticking only to each other, forming a clump or egg mass

oThe adhesiveness can either be:

1.strong and the eggs suffer damage if torn off from their substratum

2.quite weak and the eggs can be easily removed

Variations:

1.The adhesiveness gradually weakens during the course of egg development.

2.Higher salinity effects a negative influence on adhesiveness.

3.The fish eggs vary in size

The factors which determine the size of the egg are:

1. the size of the egg “kernel”

2. the thickness of the egg shell

3.size of the perivitelline space.

*The first two determine the size of the “dry” eggs (i.e., before they come in contact with water), while the third determines the size of the water-hardened eggs.

Thank you!