Photo credit: Marx Perfecto C. Garcia (Philippines)Review: Abdel Rahman El Gamal (Founder the website)
The inserted photo shows the eyelid in
a mullet specimen (Mugil sp.).
There are several
theories related to the possible roles of eyelids in fishes. It is generally
accepted that the eyelids may play a role in affecting the vision and enhance
the ability of fish to focus on specific objects. This is supported by the
presence of eyelids in deep sea fish whereas better vision and focusing would
be of top importance for the survival and well-being of fish in the deeper part
of ocean as the visibility is severely reduced. It is also believed that eye
lids serve as a physical barrier and protect fish eyes against foreign objects
in the waters.
It is questionable whether the adipose
eyelid could block out ultraviolet light
and so prevent the UV damage to the fish’s retina in some species.
Apart from above, the eyelids served as a
taxonomy tool in some fish groups such as mullets. In flathead grey mullet, Mugil cephalus, the adipose eyelid is
well developed, covering most of pupil with only a narrow slit over the pupil,
while in thin-lip grey mullet (Chelon ramada), the adipose eyelid is
poorly developed.
Photo credit: Marx Perfecto C. Garcia (Philippines)
Description: Abdel Rahman El Gamal (Founder of
the website)
The inserted picture was taken in
an aquaculture facility in China and shows several sizes of bamboo graders.
The use of bamboos in aquaculture
goes back to about a century when bamboo cages were used in Indonesia. In
countries where bamboos are abundant, bamboos have been introduced more in
aquaculture as an eco-friendly material with lower cost and easier maintenance.
Fish graders have been added to the use of bamboos.
Bamboo graders are commercially
produced at the moment. As the case with other bar graders, the thickness of
bamboo stems as well as the distance between them would determine the size of
fish retained above the grader and those that passes through for a given
species. That is why; graders are numbered according to the space between bars for
easier use.
It may need mentioning that freshly cut green bamboo are often flexible
and can be shaped and manipulated for various uses including graders. Other
treatments may be applied for the same purpose including the use of heat.
Review: Abdel Rahman El Gamal (Founder of the
website)
The removal of the premaxilla of bone of the upper lip of tilapia
males goes back to the late 1970s. The purpose of such practice is to reduce
the aggressive behavior of tilapia males and hence reduce the possible injuries
and/or mortality of females during the spawning season especially when the
mating takes place in confined places such as hapas or tanks whereas females
can be exhausted or experience scale loss that may lead to their death. This harm
is more frequent when males are much larger than females. The clipping
of the premaxilla is done using sharp scissors or razors.
As expected, in open pond breeding, the aggressive behavior of males is
not common as females usually have more chance to escape such harassment and
hence the removal of the male premaxilla is not usually required. The same is
true when females are mated with similar-sized males.
The resulting wound should be disinfected using proper disinfectants
such as potassium permanganate or a 10% solution of Betadine.
It may
worth noting that the removal of the male premaxilla does not interfere with
the reproduction or feeding activities of treated males.
This lecture on the management of fish hatcheries was delivered in Fish
Culture Development training course during August 2019. The lecture starts with
general information related to the various modes of reproduction among aquatic
animals of finfish, shell fish, mollusks and others including substrate
spawners, mouth brooders till giving birth. The levels of parental care have
been also addressed. Relying aquaculture on wild collected seeds has been
covered along with less reliability of such approach and hence the necessity to
have fish hatcheries.
The focus of the lecture has been placed on the
hatchery technology of fish species giving examples of various groups of
finfishes and crustaceans in freshwater and marine waters including acquiring
broodstock, hatchery facilities, reproduction technology (natural – artificial)
and the relationship between adopted technologies and the biology of fish as
well as the economic considerations. The lecture addressed the quality of
hatchery production whether through genetic enhancement or biosecurity measures
such as vaccination or disease-free protocols.
Photo credit: Marcel Jean Adavelo (Madagascar) – Review:
Marcel Jean Adavelo and Abdel Rahman El Gamal (Founder of the website)
As shown in the attached picture, the spawning tilapia pond
is separated by a net with appropriate mesh size that retains the broodstock in
a part of the pond while allows the produced fry and fingerlings to freely move
back and forth from/to the pond partitions.
The manual lift tray located on the pond dyke is used to
feed the fry/fingerlings as well as to collect them. As expected, the
collection process continues for the fingerlings that pass through the net
especially when attracted by feed. There will be always a possibility that some
fingerlings may grow and stay in the breeding partition and turn too large to
pass through the net. These will be sorted out upon the draining of the pond by
the end of the spawning season.
In brief, the simplicity of such system is a
main issue to promote such system in small-scale aquaculture in Madagascar and
other countries whenever the overall conditions permits.
Video credit: Fares Fares Arab (Egypt) and Marx Perfecto C. Garcia (Philippines) -Information source: Fares Fares Arab Description: Abdel Rahman El Gamal (Founder of the video channel)
This video was filmed in an intensive fish farm located in Ismailia
region, Egypt. The greenhouse has a dimension of 54×60 meters and hosts 42
grow-out circular tanks with a 7-m diameter each. The plastic lining has a 1 mm
thickness with a guaranteed durability of 10 years in sun and 15 years in shade.
The water depth in the tanks is 175 cm and the daily water exchange
rate is about 5%. The farm depends on underground water from 28-m deep well. Water
temperature during winter ranges from 21 – 23 C eliminating the need for
heating facilities. Because the salinity of well water is about 25 g/l, a
mixing with freshwater takes place to bring the salinity down in grow-out
tanks.
Fish grown in the system are all-male of either Nile tilapia
(Oreochromis niloticus) produced in a hatchery within the facility, or
red tilapia initially brought from United Arab Emirates.
The first phase of production (not seen in the video) is
done in an outside hatchery and fingerling ponds where tilapia fry are grown on
natural food for three months ending by juveniles of about 70-g average size
which are moved in the greenhouse where they are stocked at a density of 110
fish/m3. The grow-out cycle
is 3 months with a target production of 1.5 ton/tank (25 kg/m3). The
average harvest size is 250 g. Feed used is commercial floating feed of 30%
protein. The management of the farm adopts the harvest every about 10 days.
The greenhouse shown in the video is phase one
while there is phase two has been prepared as shown in the end of the video.
There is also about one hectar of land that is planned for the completion of integration
between the aquaculture facility and vegetable crops.
This lecture has been delivered by Dr. Abdel Rahman El Gamal
during August 2019 as a contribution to the “Fish Culture Development training
course – Africa” which is annually organized by the Egyptian International
Centre for Agriculture (EICA) with the support by Japan International
Cooperation Agency (JICA). The introductory part of the lecture addressed the
key issues especially those related to the applications of genetics in
aquaculture which addressed the management of broodstock (with a special emphasis
on effective breeding number), selection methodologies (for single or multiple
traits), hybridization, ploidy induction (triploidy – tetraploidy) and ending
by advanced technologies such as gynogenesis, androgenesis and genetic
engineering. This updated lecture included more details on the heritability of
some economical traits in selected fish species. The main breeding issues such
as inbreeding, genetic bottlenecks, selection plateau and others have been
addressed in this lecture. The genetic background in the sex reversal of
tilapia fry has been covered in the lecture.
The possible genetic concerns regarding the stocking enhancement programs have been also addressed. Diagrams and case studies have been brought in to support the lecture. Fish genetics, application of fish genetics in aquaculture, heritability coefficient, selection, selection index, selection index, selection plateau, effective breeding number, hybridization, reciprocal cross, sex reversal of tilapia, triploidy, tetraploidy, gynogenesis, androgenesis, genetics in stock enhancement..
The
inserted pictures belong to Omani abalone, Haliotis mariae. In the absence of external signs of sexual
dimorphism for the shell structure, the sexing of abalone cannot be done based
on the external differentiation and is only determined through the visual
inspection of gonads which could be seen if the foot and mantle are forced away
from the right side.
Male gonads tend to be from white to creamy
beige in color while females’ ovaries are usually darker; greyish-green. In
spent females, the color of gonads often fades.
This lecture was delivered in aquaculture development training course hosted by the Egyptian International Centre for Agriculture (EICA).
This updated lecture presents not only statistics of 2017 but emerging practices such as biosecurity system as well as specific issues has been highlighted in this lecture such as the problems facing the shrimp aquaculture.
The contribution of aquaculture to the total fishery over years has been illustrated. The same is true regarding the major contribution of tilapia in Egyptian aquaculture and the means attempted to expand the production basket.
The position of Egyptian aquaculture regarding global aquaculture has been tabulated showing that in 2017 Egypt ranks 6th in regard to world aquaculture.
Photo credit: DO Xuan Hai (Vietnam) Description: Abdel Rahman El Gamal (Founder of the website)
The inserted
photos regarding the artificial reproduction of rabbitfish (Siganus guttatus)
were taken during a training course conducted in the Philippines. The high
economic value of this tropical food marine species encouraged its culture that
relied mostly on the fingerlings captured from the wild.
As the case with many farmed fish, the artificial propagation is
found to be the reliable approach towards sustainable production of the
species.
The hormonal spawning induction trials used human chorionic gonadotropin
(hCG), LHRH-analog, or carp pituitary extract whether given either individually
or in combination.
