Saturday, October 7, 2023
Thursday, October 5, 2023
Copepods as fish food organisms
Copepods
Copepods are common zooplankton both in freshwater and in brackish water. Their advantages being wide range of body size within and between species. They are natural feeds for larvae and juveniles of many finfish and crustaceans. The early stage nauplii and copepodites can be extremely useful as initial prey for species that have very small mouth gape at first feeding.
In the wild, most marine larvae feed on copepod eggs and nauplii during the first few weeks of life. Since a number of larval fish cannot be reared using rotifers as the first feed but have to be reared on either laboratory reared or wild caught copepod nauplii. Adult copepods range from 0.5 to 5.0 mm. The larval stages consist of six naupliar and six copepodite stages.
4.2. Copepod classification
Kingdom :Animalia
Phylulm :Arthropoda
Sub-phylum : Crustacea
Class
: Maxillopoda
Sub-class
: Copepoda
4.3. Biology and life cycle of copepods
Most
adult copepods have a length between 1 and 5 mm. The body of most copepods is
cylindriconical in shape, with a wider anterior part. The trunk consists of two
distinct parts, the cephalothorax (the head being fused with the first of the
six thoracic segments) and the abdomen, which is narrower than the
cephalothorax. The head has a central naupliar eye and unirameous first
antennae that are generally very long. Planktonic copepods are mainly suspension
feeders on phytoplankton or bacteria; the food items being collected by the
second maxillae. The male copepods are commonly smaller than the females and
appear in lower abundance than the latter. The eggs hatch as nauplii and after
five to six naupliar stages (moltings), the larvae become copepodites. After
five copepodite moltings the adult stage is reached and molting is ceased. A
diapause stage is present in the development of the copepods so as to survive
adverse environmental conditions, such as freezing. The major diapause habitat
is the sediment, although a minor part of the diapausing individuals may stay
in the planktonic fraction, the so-called “active diapause”. Harpacticoid copepods
are less sensitive and more tolerant to extreme changes in environmental
conditions (i.e. salinity: 15-70 g/l; temperature: 17-30°C) than calanoids and
thus are easier to rear under intensive conditions. Moreover, harpacticoids
have a higher productivity than calanoids and can be fed on a wide variety of
food items, such as microalgae, bacteria, detritus and even artificial diets.
However, as mentioned previously, care should be taken in this respect as the
lipid and (n-3) HUFA composition of the copepods is largely dependent on that
of the diet fed.
4.4. Candidate species and culture techniques
The
main suborders of copepods found in brackishwater are calanoids (Acartia, Calanus and Pseudocalanus
spp.), harpacticoids and cyclopoids.
Herbivorous copepods are primarily filter feeders and typically feed on very
small particles. But they can feed on larger particles, which give them an
advantage over the rotifers. Copepods can also eat detritus. Calanoida is an
important order of copepods, a kind of zooplankton. They include 43 families
with about 2000 species of both marine and freshwater copepods. Calanoid
copepods are important in many food webs, taking in energy from phytoplankton
and algae and 'repackaging' it for consumption by higher trophic level predators
like birds, fishes and mammals. Many commercial fishes are dependent on
calanoid copepods for diet in either their larval or adult forms. Baleen whales
such as the bowhead whale eat copepods of the genera Calanus and Neocalanus.
4.5. Culture techniques
A
continuous production system for the calanoid copepod Acartia tonsa consists of three culture units: basis tanks, growth
tanks and harvest tanks. The Acartia
tonsa are isolated from natural plankton samples or reared from resting
eggs onwards. The basis tanks (200 l grey PVC tanks: 1500 x 50 cm) are run
continuously and the eggs produced are used to adjust population stocks. These
tanks are very well controlled and kept under optimal hygienic conditions:
using filtered (1 μm) sea water (salinity 35 g/l) and fed with Rhodomonas
algae. Temperatures are kept at 16-18°C and a gentle aeration from the bottom
is provided. Adult concentrations with a ratio of 1:1 males to females are
maintained at less than 100 per l by adjusting once a week with stage IV - V copepodites.
Approximately 10 l of the culture water is siphoned daily from the bottom of
the tanks (containing the eggs), and replaced by new, clean seawater. Eggs are
collected from the effluent waters by the use of a 40 μm sieve; production
averaging 95,000 eggs/day, and corresponding to a fecundity rate of 25 eggs/
female per day. The basis cultures are emptied and cleaned two to three times
per year, by collecting the adults on a 180 μm sieve and transferring them to
cleaned and disinfected tanks. Collected eggs are transferred to the growth
tanks where maximal densities reach 6000/l. The nauplii start to hatch after 24
h with hatching percentages averaging 50% after 48 h incubation. Initially Isochrysis is given at a concentration
of 1000 cells ml/1 and after 10 days a mixture of Isochrysis and Rhodomonas
administered at a concentration of 570 and 900 cells ml/1, respectively. The
generation time (period needed to reach 50% fertilized females) is about 20
days with a constant mortality rate of about 5%/day. After 21 days, the adults
are collected using a 180 μm sieve and added either to the basis or harvest
tanks. Harvesting tanks are only in use once the fish hatchery starts to
operate. Cultures are maintained in 450 l black tanks under the same conditions
as described above. Each tank receives a daily amount of 16 X 108 Rhodomonas cells, harvested from bloom
cultures. These tanks are emptied and cleaned more regulary than stock tanks.
To facilitate the harvesting of solely nauplii or copepodites of a specific
stage (depending on the requirements), eggs are harvested daily and transferred
to the hatching tanks; the aeration levels within these tanks being increased
to maintain 80% oxygen saturation. Nauplii of appropriate size (and fed on
Isochrysis) are harvested on a 45 μm screen and by so doing cannibalism by the
copepod adults is also minimized.
4.5.1. Use of resting eggs
Many
temperate copepods produce resting eggs as a common life-cycle strategy to
survive adverse environmental conditions. Resting eggs can tolerate drying at
25°C or freezing down to - 25°C and that they are able to resist low
temperatures (3-5°C) for as long as 9 to 15 months. These characteristics make
the eggs very attractive as inoculum for copepod cultures. Samples of sediments
rich in resting eggs can be stored in a refrigerator at 2-4°C for several
months. When needed, the sediment containing the resting eggs is brought in
suspension and sieved through 150 μm and 60 μm sieves. The resting eggs is then
immersed in the disinfectant, (i.e. FAM-30 or Buffodine); surface-disinfection
being needed to eliminate contaminating epibiotic micro-organisms. After
disinfection, the eggs are then washed with 0.2 μm filtered sterile seawater
and transferred to disinfected culture tanks or stored under dark, dry and cool
conditions. Before, starting the surface-disinfection procedure attention must
be paid to the physiological type of resting eggs. Some marine calanoids are
able to produce two kinds of resting eggs, i.e. subitanous and diapause eggs.
Since subitanous eggs only have a thin vitelline coat covering the plasma
membrane, they are more susceptive to disinfectants than the diapause eggs
which are enveloped by a complex four-layer structure.
Cladocerans as Fish food organisms
Cladocerans
Cladocera or Cladocerans are small crustaceans commonly called water fleas, They are part of the Class Branchiopoda. They have soft body and are small in size therefore they form an important part in fish culture specially seed rearing process. A brief of Cladocerans is as follows
3.1.Cladocerans classification
Kingdom - Animalia
Phylum - Arthropoda
Sub-phylum - Crustacea
Class - Branchiopoda
Sub-class - Phyllopoda
Order – Cladocera
3.2. Biology and nutritional value of cladocerans
In
contrast to the prosperity of cladocerans in freshwater systems, with more than
600 recorded species, marine cladocerans show a very low diversity, with only
eight truly marine species. These 8 species can be divided in two distinct
groups, the Podonidae (represented by the genera Evadne, Pleopis, Podon and
Pseudevadne), and the Sididae with only one species, Penilia avirostris).
3.2.1. Daphnia
The
most commonly known genus is Daphnia (freshwater fleas), which is the most
researched in this group and Moina. Cladocerans are free-swimming organisms,
and most orientate themselves with dorsal side up. The head is typically
separated from the body by a deep indentation, but also may not be separated.
It projects forward as a beak or rostrum. On the forehead is an unpaired
compound eye, a result of two fused eyes, and, in most species, a simple
naupliar eye.
3.2.1.1. Daphnia classification
Kingdom: Animalia
Phylum: Arthropoda
Sub-phylum: Crustacea
Class: Branchiopoda
Order: Cladocera
Family: Daphniidae
Genus: Daphnia
3.2.1.2. Nutritional value of Daphnia
The
nutritional value of Daphnia depends strongly on the chemical composition of
their food source. However, since Daphnia is a freshwater species, it is not a
suitable prey organism for marine organisms, because of its low content of
essential fatty acids and in particular (n-3) HUFA. Furthermore, Daphnia
contains a broad spectrum of digestive enzymes such as proteinases, peptidases,
amylases, lipases and even cellulase that can serve as exoenzymes in the gut of
the fish larvae.
3.2.1.3. Nutritional value of Moina
The
nutritional content of Moina varies considerably depending on their age and the
type of food they are receiving. Although variable, the protein content of Moina
usually averages 50% of the dry weight. Adults normally have a higher fat
content than juveniles. The total amount of fat per dry weight is 20-27% for
adult females and 4-6% for juveniles.
3.2.1.4. Biology and life cycle of Daphnia
Daphnia
is a frequently used food source in the freshwater larviculture (i.e. for
different fish species). Daphnia are small crustaceans that are almost
exclusively living in freshwater. The head projects ventrally and somewhat
posteriorly in a beak-like snout. The trunk appendages (five or six pairs) are
flattened, leaf-like structures that serve for suspension feeding (filter
feeders) and for locomotion. Species of the genus Daphnia are found from the
tropics to the arctic in habitats varying in size from small ponds to large
freshwater lakes. The adult size is subjected to large variations; when food is
abundant, growth continues throughout life and large adults may have a carapace
length twice that of newly-mature individuals. Normally there are 4 to 6 Instar
stages; Daphnia growing from nauplius to maturation through a series of 4-5
molts, with the period depending primarily on temperature (11 days at 10°C to 2
days at 25°C) and the availability of food. Daphnia species reproduce either by
cyclical or obligate parthenogenesis and populations are almost exclusively
female. Eggs are produced in clutches with parthenogenetic eggs produced
ameiotically and result in females, but in some cases males can appear.
Factors, such as change in water temperature or food depreviation as a result
of population increase, may induce the production of males. The fertilized eggs
are large, and only two are produced in a single clutch (one from each ovary),
and are thick-shelled: these resting or dormant eggs being enclosed by several
protective membranes, the ephippium.
Life
cycle of Daphnia
3.2.2. Moina
Various
species includes Moina affinis, M. australiensis, M. belli, M. brachiata, M. brachycephala, M. flexuosa, M. hartwigi,
M. hutchinsoni, M. macrocopa, M. micrura, M. minuta,
M. mongolica, M. rectirostris, M. reticulata,
M. salina and M. tenuicornis. Adult Moina have an average size (700-1,000 µm) and
are approximately the same size or only slightly larger than adult rotifers and
smaller than newly-hatched brine shrimp. Moina are ideally suited for feeding
freshwater fish fry as they have a longer life span. Moina micrura grown in ponds, fertilized with mostly chicken manure
or, less frequently, with pig manure, are used as the sole food for fry of many
ornamental tropical fish species, with a 95-99% survival rate.
3.2.2.1. Moina classification
Kingdom: Animalia
Phylum: Arthropoda
Sub-phylum: Crustacea
Class: Branchiopoda
Order: Cladocera
Family:
Moinidae
Genus:
Moina
3.2.2.2. Life Cycles of Moina
The
reproductive cycle of Moina has both a sexual and asexual phase. Normally, the
population consists of all females that are reproducing asexually. Under
optimum conditions, Moina reproduce at only 4-7 days of age, with a brood size
of 4-22 per female. Broods are produced every 1.5-2.0 days, with most females
producing 2-6 broods during their lifetime. Under adverse environmental
conditions, males are produced and sexual reproduction occurs resulting in
resting eggs (ephippia). The stimuli for the switch from asexual to sexual
reproduction in populations of Moina is an abrupt reduction in the food supply,
resulting in an increase in resting egg production. However, it is advantageous
to keep the population well fed and in the asexual mode of reproduction, since
fewer progeny are produced with resting eggs.
3.2.2.2.1. Production and use of resting eggs
Resting
eggs are interesting material for storage, shipment and starting of new Daphnia
cultures. The production of resting eggs can be initiated by exposing a part of
the Daphnia culture to a combination of stressful conditions, such as low food
availability, crowding of the animals, lower temperatures and short
photoperiods. These conditions are generally obtained with aging populations at
the end of the season. Collection of the ephippia from the wild can be carried
out by taking sediment samples, rinsing them through a 200 μm sieve and
isolating the ephippia under a binocular microscope. Normally, these embryos
remain in dormancy and require a diapause inhibition to terminate this status,
so that they can hatch when conditions are optimal. Possible diapause
termination techniques are exposing the ephippia to low temperatures, darkness,
oxygen and high carbon dioxide concentrations for a minimal period of several
weeks (Davison, 1969). There is still no standard hatching procedure for
Daphnia. Generally the hatching process is stimulated by exposing the ephippia
to higher temperatures (17-24°C), bright white light, longer photoperiods and
high levels of dissolved oxygen. It is important, however, that these shocks
are given while the resting eggs are still in the ephippium. After the shock
the eggs may be removed from the ephippium. The hatching will then take place
after 1-14 days.
Collect Moina/Daphnia
from stagnant water bodies like ponds and tanks with
the help of a scoop net having 100-200 µ mesh.
Place the content in a plastic bucket.
Dilute the
sample by adding clear water and examine under a microscope to pick up Moina/Daphnia
with help of a dropper.
Inoculate Moina/Daphnia
@ 1-2 nos./ 10 ml of filtered water in a 20 ml glass tube.
Feed Moina/Daphnia with yeast or groundnut oil cake @200 ppm.
After 3-4 days, transfer the test tube cultures into 1 liter glass jar or beaker and feed with yeast.
After 5-6
days, use this cultures
for further inoculation in mass culture tanks.
Steps of c mass culture
For mass culture, 500-1000 litre capacity cement cistern or plastic pools.
Wash the culture tank thoroughly with clean ground water or 1% KMnO4.
Fertilize the tank with slurry @ 3-4 ml/liter for 3-4 days regularly.
On 3rd or 4th day of fertilization, inoculate the tank with Moina/Daphnia @
40-50 individual/litre.
In about 6-7 days, Moina/Daphnia multiplies and reaches to a peak density, ranging from 10,000-25,000 individual/litre.
Harvest the Moina/Daphnia in morning or late evening.
Wednesday, October 4, 2023
Pond preparation for aquaculture
Pond preparation
In any earthen pond culture system the bottom soil play
important role infish production. High organic matter content in neutral soil
often promotes higher primary productivity and hence higher fish yield. Natural
food organisms are one of the most important food sources in ponds. It is rich
in protein, vitamins, minerals and other essential growth elements that simple
supplementary feed cannot complete. Fish yield in pond can also be affected by
the presence of predators, deteriorating water quality and improper pond
management. Hence, pond preparation is a first step towards ensuring higher
fish production. It includes pre-stocking and post stocking management
practices. Pre-stocking pond preparation includes soil sampling , drying,
manuring and fertilization, weed control, insect control , predatory and
weed fish control. Post stocking pond
management includes the other steps which support a good yield like natural
plankton production, disease free aquatic environment, weed control, management
of various pond structures application of inputs as and when necessary and
regular monitoring of growth.
A brief description of pond preparations steps are given
below.
13.1. Soil sampling:- Prior to pond preparation,
soil samples are collected from the pond bottom, dikes for pH, organic matter
and important nutrient contents analysis. 12 soil samples from 0-15 cm top soil
are collected from one ha pond area in S- shaped pattern. Soil in sieved to
remove stones, wooden material and coarse particles. All the samples are dried
in air and labeled after mixing sub samples properly. The dried soil is then
packed in labeled plastic bag and analysis for its composition. Soil pH
analysis is generally conducted to determine nature of the soil if acidic or
basic. For newly developed ponds where acid sulphate soils are found lime
application rate can be calculated based on pH of soil. When acidic soil
condition is detected, corrective measures can be incorporated in the pond
preparation activities. Calcium sulfate (CaSO4.2H2O) are
used in soil having alkaline pH.
13.2. Leaching :-If
the soil is acidic it is flushed with freshwater to dissolve the acids, salts
undesirable metallic compounds like aluminum, iron and excess sulfur ions are
washed out.
13.3. Pond drying:-The
pond bottom is exposed to sun light and air to eradicate undesirable fish
species, insects and disease causing agents. Soil exposure to air and light
also fasten the mineralization of organic matter. Harmful gases trapped in the
bottom soil are also released. The pond is dried until the soil cracks or when
it is firm enough to hold one's weight without sinking more than 5 cm on
walking over the surface. While drying other activities like repair of dikes
and inlet and outlet gates, leveling, installation of screens and substrates
installation if required are undertaken.
13.4. Tilling:-Tilling or ploughing of
bottom soil improves soil quality by exposing subsoil to the atmosphere thereby
speeding up the oxidation process. It also helps to turn the sub surface soil
nutrients and their subsequent utilization to improve the pond productivity.
13.5. Liming:-Lime are the materials
which contain calcium and magnesium compounds and are capable of neutralizing
acidity. Most common liming materials are oxides, hydroxides and carbonates of
calcium and magnesium having higher percentage of calcium compared to
magnesium. (a) CaO - Calcium oxide or Quick lime (b) Ca(OH)2 Calcium hydroxide or slacked lime, (c)
CaCO3- Calcium carbonate agricultural lime are the commonly
occurring forms of limes. Calcium
carbonate is most widely used lime in aquaculture.
13.6.
Liming substances:- Liming
substances are the following:
(a) Calcium oxide (CaO):- Calcium oxide is
variously known as unslaked lime, burnt lime and quicklime. It is manufactured
by roasting calcitic limestone in a furnace. Calcium oxide is caustic and
hygroscopic and is sold commercially in powder and granular forms.
(b) Calcium hydroxide (Ca(OH)2):-Calcium
hydroxide is referred as flaked lime, hydrated lime, slaked lime or builder's
lime. It is prepared by hydrating calcium oxide. It sold commercially in powder
or granular forms.
(c) Calcium carbonate ( CaCO3) and
mixed calcium-magnesium carbonate, [CaMg (CO3)2]:-The
carbonates occur widely in nature. Among the common forms that can be utilized
as liming substances are calcitic limestone which is a pure calcium carbonate
and dolomitic limestone which is a calcium-magnesium carbonate with varying
proportions of calcium and magnesium. Commercial calcium carbonate is known as
agricultural lime. The carbonates are the least reactive of the three liming
substances.
13.7.
Action of liming:- The
favorable actions of liming are: (a) kills most micro-organisms especially
parasites due to its caustic reaction, (b) raised pH of acidic water to neutral
or slightly alkaline value, (c) increases the alkaline reserve in water and mud
which prevents sudden fluctuation in pH, (d) neutralizes the harmful action of
sulfides and acids, (e) promotes biological productivity since it enhances the
breakdown and degradation of organic substances by bacteria creating a more
favorable oxygen and carbon reserves, (f) precipitates suspended or soluble
organic materials, decreases biological oxygen demand (BOD), increases light
penetration, enhances nitrification due to the requirement of calcium by
nitrifying organisms. Excessive liming, however, can be damaging because it
decreases phosphorus availability through precipitation of insoluble calcium or
magnesium phosphate.
Commonly occurring chemical reaction in pond
water are as follows
CO2 in water is mainly produced as
a result of respiration and degradation of organic matter. CO2 is
three times more soluble in water than oxygen. It reacts with water
and form carbonic acid (H2CO3) which is a weak acid and
breaks up into H++ HCO3- ions. In presence
of carbon dioxide CaCO3
dissolve in water and form calcium bi carbonate Ca(HCO3).This is
stable product present in excess of CO2. In Presence of Acid and
base different reaction occurs.
13.8.
Methods of liming
Liming can be done in three
different ways:
·
Broadcast
over dried pond which includes the dike walls.
·
Mixing
with water and spraying over the pond, and
·
Liming
the flowing water into the pond.
In general, any one of
these methods may be employed. When we are using the first two methods, lime
should be spread as uniformly as possible over the complete surface of the pond
or pond water. The third method is uncommonly practices although it saves the
labor in spreading.
Agricultural wastes like
basic slag, cement factory wastes, paper mill sludge have also been found to be
suitable for use as liming materials as they contain good amount of CaO. Rock
phosphate containing calcium besides phosphorous may be used as a source of
phosphorous in acid soils but only to a
limited extent due to its effectiveness under moderately acid condition which
is rather undesirable for fish ponds.
13.9. Fertilization:-One
usual way of increasing carrying capacity of a pond is to improve its natural
fertility through the addition of organic or inorganic fertilizers. Pond
fertilization is an important and necessary step in extensive and
semi-intensive methods of farming operations.
(a)
Organic manures
Proximate nutrient content
of certain oil cakes are as follows
|
Oil cake |
Nitrogen % |
Phosphorous% |
Potash% |
|
Ground nut oil cake |
6.0-6.5 |
0.8-1.0 |
0.8-1.0 |
|
Mustard oil cake |
4.0-4.5 |
1.0-1.6 |
1.0-1.5 |
|
Madhuka seed cake |
2.0-2.5 |
0.5-0.8 |
1.5-1.9 |
|
Neem cake |
4.5-5..0 |
0.8-1.0 |
1.0-1.5 |
Animal wastes also
strengthen the food chain ensuring easy availability of natural fish food
organisms that support the fish growth. The nutrient content in the different
animal waste are as follows
|
Animal wastes |
Nitrogen % |
Phosphorous% |
Potash% |
|
Cattle dung |
0.4-0.5 |
0.2-0.4 |
0.1-0.2 |
|
Pig dung |
0.4-0.6 |
0.3-0.6 |
0.2-0.4 |
|
Duck droppings |
0.6-0.9 |
0.3-0.6 |
0.4-0.6 |
|
Vermicompost |
0.4-1.4 |
0.1-0.25 |
|
(b)
Inorganic
fertilizers
Inorganic fertilizers are
synthetic fertilizers containing pure form of nutrient. When inorganic
fertilizers are applied in pond immediately they are dissolved in water to
release contained nutrient. Nitrogen,
phosphorus, potash calcium, magnesium, sulphur are macronutrients while copper,
iron, iodine, selenium, zinc, cobalt, chromium are some of the micronutrients.
Nitrogen is required for the synthesis of
protein in living beings. In soil and water it can be supplemented by
application of urea, calcium ammonium nitrate, potassium nitrate, ammonium
sulfate, ammonium nitrate, sodium nitrate and liquid nitrogen. In pond average
amount of urea applied is 20.0 kg/ha/month.
Nitrogen content present in
some of the inorganic fertilizers are
|
Inorganic fertilizers |
Formula |
Nitrogen content |
|
Urea |
CO(NH2) |
44-46% |
|
Calcium nitrate |
Ca(NO3)2 |
15% |
|
Ammonium nitrate |
(NH4)2NO3 |
33 |
|
Ammonium sulfate |
(NH4)2SO4 |
21 |
|
Sodium nitrate |
NaNO3 |
16 |
|
Potassium nitrate |
KNO3 |
13 |
Phosphorous in fresh water
ponds affect pond productivity.
Phosphorous is useful in the synthesis of cell wall of plant and animal
cells and tissues. The main form of inorganic phosphate fertilizers are as
follows
Phosphorous is also
released in water as a result of degradation of plant and animal remains. The
availability of phosphorous to a large extent depends on the soil pH. It is
more available at neutral pH. If the pH is acidic it combines with the Aluminum
present in the water and form Aluminium phosphate. Under alkaline conditions it
combines with calcium and form calcium phosphate. These complexes make
phosphorus unavailable minimizing the phytoplankton production. Mostly in pond
single super phosphate is used in pond water the normal rate is 25 kg/ha/yr.
|
Name of fertilizer |
Formula |
Phosphorous
content in % |
|
Single super phosphate |
|
|
|
Diammonium phosphate |
(NH4)2HPO4 |
20-23 |
|
Tripple super phosphate |
Ca(H2PO4)2 |
7-22 |
|
Rock phosphate |
|
12-17 |
|
Nitrophosphate |
Ca(H2PO4)2H2O |
10-15 |
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