Mengatasi air hijau pada kolam

Air  hijau dalam kolam koi adalah momok bagi pengemar Koi, air yang berwarna hijau tidak hanya membuat pemandangan di kolam tidak indah juga membuat Koi tidak bisa dinikmati keindahannya. Problem air kolam berwarna hijau atau Green water sangat biasa terjadi dan dialami para penggemar koi. Air kolam koi yang berwarna hijau disebabkan oleh ledakan populasi ganggang (algae) di dalam kolam atau biasa disebut Algae Booming . Ganggang merupakan fitoplankton yang berukuran sangat kecil dalam orde mikron yang hidup di dalam air kolam koi. Sebagaimana tumbuhan lainnya ganggang mengkonsumsi Ammonia untuk tumbuh dan berkembang, sehingga ganggang akan tumbuh dengan sangat subur jika terdapat Ammonia yang cukup di dalam air. Semakin tinggi kandungan  amonia  di kolam  koi akan membuat kolam menjadi cepat berwarna hijau.

Ammonia di dalam kolam koi dihasilkan dari kotoran ikan koi, sisa makanan, hewan mati dan tumbuh-tumbuhan mati yang membusuk di dalam kolam. Biasanya pertumbuhan ganggang akan berlangsung dengan pesat pada saat suhu di dalam kolam mulai meningkat terutama pada musim panas dan kemarau. Problem air  hijau di kolam koi tidak bisa diatasi dengan menggunakan filter mekanis karena ukuran ganggang yang sangat kecil yang tidak memungkinkan disaring.

Untuk mengatasi masalah air hijau pada kolam koi perlu dicari sebab utamanya. Ada beberapa kondisi ideal yang memungkinkan algae tumbuh dan berkembang dengan baik. Karena itu solusi untuk mengatasinya adalah mengurangi atau menghilangkan kondidi-kondisi ideal ganggang tumbuh dan berkembang. Kondisi ideal untuk algae tumbuh pesat jumlahnya adalah:

  1. Suhu air di dalam Kolam yang hangat, Algae tumbuh dengan baik di suhu  air yang hangat. Pada musim kemarau atau musim panas suhu air di dalam kolam cenderung meningkat sehingga memungkinkan ganggang tumbuh dengan baik.
    2. Sinar Matahari yang penuh di dalam kolam, Sebagaimana halnya tumbuhan lain di , algae memerlukan sinar matahari untuk melakukan fotosintesis. Pada kolam outdoor sinar matahari akan secara penuh masuk ke dalam kolam sehingga Algae dapat tumbuh dengan baik.
    3. Sisa  Makanan Koi yang berlebih, sisa makanan ikan yang berlebih akan  membusuk dan menghasilkan ammonia. Amonia merupakan nutrisi yang baik untuk pertumbuhan ganggang.
    4. Kotoran Koi menghasilkan Amonia. Kotorabn Koi yang mengandung ammonia akan membuat algae tumbuh dengan subur.

Jika sebagian atau keseluruhan  syarat tersebut  terpenuhi, ganggang di kolam koi akan  tumbuh dengan baik dan air akan menjadi  berwarna hijau (booming algae). Karena itu  Kunci untuk membersihkan air hijau adalah dengan menghilangkan  atau meminimalkan kondisi ideal untuk pertumbuhan mereka.

Untuk mengendalikan pertumbuhan  Algae di kolam ikan koi dapat dilakukann dengan beberapa cara. Bisa dipilih cara yang tepat atau kombinasi  beberapa cara yang paling mungkin dan efisien.

1. Menaungi Kolam Koi

Kehangatan air dan ketersediaan cahaya untuk fotosintesis dipengaruhi  oleh sinar matahari yang masuk ke dalam kolam koi. Menaungi  kolam akan mengurangi cahaya matahari di kolam. Jika cahaya yang masuk berkurang maka pertumbuhan ganggang akan terhambat Menaungi kolam dapat dilakukan dengan memasang atap atau dengan menanam pohon di sekitar kolam. Menanam pohon di sekitar kolam bisa membuat  kolam kotor oleh daun-daunan yang terjatuh.

2. Buang Semua Kotoran Yang menghasilkan Ammonia

Menghilangkan kotoran baik yang bersifat fisik maupun kimia. Pembuangan ini dilakukan dengan memasang sistem filter kolam koi yang baik dan tepat. Sistem Filter fisik menghilangkan sebagian besar bahan organik yang membusuk di kolam. Filter kolam koi harus memiliki kapasitas  tidak kurang dari 10% dari volume kolam koi, idealnya adalah 30% Volume kolam. Air yang sudah masuk ke dalam filter dikembalikan lagi ke dalam kolam dalam bentuk yang sudah bersih menggunakan pompa. Pompa ini  harus mampu mengalirkan seluruh volume air kolam  dalam satu jam/satu siklus putaran dalam satu jam. Misalnya volume kolam adalah 6000 liter, maka kemampuan pompa haruslah 6000 liter/jam dan volume filter 1800 liter.

Filter kolam koi biasanya memiliki beberapa chamber, filter mekanis, filter biologis dan kimia.Material yang tidak mampu di sharing dengan  filter mekanis difilter dengan filter biologi dan kimia. Pada ruang filter biologis bakteri tertentu mengubah amonia menjadi nitrit ini, yang selanjutnya dikonversi oleh bakteri lain ke nitrat. Nitrat kurang berbahaya daripada kedua, tetapi mereka kuat pupuk untuk semua tanaman di dalam kolam, termasuk ganggang.

3. Menambahkan tanaman pada ruang filter

Tanaman akan mengkonsumsi amonia untuk kelangsungan hidupnya. Dengan memberikan tanaman air pada ruang filter akan mengurangi makanan untuk algae sehingga tidak dapat tumbuh dengan  baik.

4. Memberikan Zat Water Cleaner

Water Cleaner menggunakan metode kimia untuk mengendalikan algae, Water cleaner akan membunuh algae  atau menghambat semua jenis ganggang  yang ada dalam air. Karena water cleaner merupakan zat racun , maka perlu berhati-hati dalam menggunakannya. Dalam dosis yang berlebihan akan dapat meracuni ikan koi.

5. Menambahkan Carbon Aktif  dan Batu Zeolit

Karbon aktif dapat menyerap zat-zat kimia berbahaya di dalam kolam koi demikian pula dengan Batu zeolite.

6. Menambahkan Lampu Ultra Violet

Sistem lampu ultraviolet yang dirancang untuk membunuh alga dan membuat mereka menggumpal, selanjutnya algae yang sudah mati dapat disaring dengan filter mekanis. Lampu UV secara efektif dapat  menghilangkan air hijau di kolam koi dalam waktu singkat.

7. Mengganti air sebagian secara periodik.

Mengganti air secara periodik  10-30%  dari volume air kolam akan membantu mengurangi kandungan amonia dalam air , jika diperlukan dapat dilakukan  setiap hari. Jika tidak, Anda bisa  dilakukan penggantian air kolam sebagian setiap minggu. Jangan mengganti air kolam keseluruhan , karena kondisi air yang sudah mature akan kembali dari nol. Ikan perlu beradaptasi lagi dan sistem filter biologis tidak bekerja secara sempurna.

Cara-cara tersebut merupakan beberapa alternatif yang bisa dipilih agar  dapat mengurangi dan menghilangkan air hijau di kolam. Pada dasarnya air hijau di dalam kolam koi dapat diatasi dengan sistem filter kolam yang baik dan mumpuni. Karena itu jika kolam koi berwarna hijau periksa sistem filternya, dari mulai rancangannya, volumenya, kapasitas pompa dan lain-lain.

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Better Management Practices For Tilapia Cage Farming In Vietnam

 

Tilapia cage farming

The aquaculture sector has increasingly played a vital role in meeting the growing global demand for food. This role has internationally widely recognised in recent years. Freshwater aquaculture has been commonly practiced in the Mekong Delta region for centuries, providing livelihoods to poor rural people as well as food supplies, employment and income.

Cultivation of fish in cages is a dominant type of freshwater aquaculture in the southern provinces of Viet Nam and the Mekong Delta. Due to limited land availability, cage culture of fish in Tien Giang has expanded by effectively taking full advantage of the available water resources.
Tilapia cage farms are the most popular freshwater cultivation practice in Tien Giang which has contributed substantially to livelihoods, food demand and poverty alleviation. However, this type of floating fish cultivation is increasingly facing difficult challenges, including a deterioration in water quality and fish mortalities. Safe environments and clean water are required to underpin the sustainability of tilapia cage farming in Tien Giang.

Study location and methodology

Tien Giang is about 70 km from Ho Chi Minh City and has a total area of about 2,482 km2. It is situated in the northeastern Mekong Delta and stretches about 120 km along the north bank of theTienRiver (one of the tributary ends of the MekongRiver) and has a 32 km border with the EastSea.

Tien Giang is the fifth largest producing province in the Mekong Delta, and the fourth in terms of total culture area. The total area under fish cultivation (mainly catfish) was 400 ha and fish production was 27,000 tonnes in 2005.
Thoi Son Islet is located in the TienRiver, close to My Tho City, and is one of the major tilapia (Oreochromis niloticus) cage farming areas of Tien Giang. The location of Tien Giang and Thoi Son Islet are shown in the satellite view on the adjacent page.
On-site sampling, laboratory analysis and questionnaire surveys were deployed to collect data from the local cage farmers. Surveys and sampling were conducted over three seasons in 2009 (dry, rainy and transitional seasons). Information collected using semi-structured checklists in questionnaire sets included:
  •  Data on socio-economic aspects such as age, education level, investment costs and stakeholders’ concerns regarding the long-term environmental sustainability of intensive farming systems; and
  • Data relating to farming activities such as seed supply, water use, stocking density, feeds, feed management, disease issues and health management.

SPSS 13.0 for WINDOWS and Excel software were used to analyse frequencies, case summaries, and to conduct T-test, one-way ANOVA and linear regression in order to understand the socio-economic situation, environmental issues and improve production of farming in fish cages.

Tilapia cultivation practices and emerging issues

The practice of farming fish in floating cages has been underway in Tien Giang for ten years and is the predominant fishery activity along the TienRiver. Not surprisingly, the Tien Giang aquaculture sector has annually provided around 18,000 tonnes of fish meat and substantially created job for more than 3,000 people and 10,000 workers relating to services and household levels.

About 145,000 m3 of total area of water surface is being used for fish cage farms. There were approximately 1,573 floating cages throughout four major districts, comprising: Chau Thanh, My Tho, Cai Lay and Cai Be. In the first five months of 2009 alone, 128 new floating cages were constructed and 1,046 tonnes of fish were harvested (Table 1).
Presently, farmers culture tilapia year around and are using more pellet feed and chemicals than previously due to higher stocking densities, water quality deterioration and consequently disease during off-seasons, especially during the floods.
Most cages are topped with wooden frames which are also home for the farmers. Cage components consist of a frame, mesh or netting, feeding ring, lid and flotation. Cage shapes may be square or rectangular. The most common cage size is: 4 x 8 x 3 m (length x width x depth). Cages may be categorised as small (less than 100 m3) and medium (from 100 to 500 m3).
About 74 per cent of the cages are small and this influences the method of harvest and the cage farmers’ finances in Thoi Son Islet.

Water quality

Cages are floated in clusters along the banks of the TienRiver and concentrated in My Tho City. However, there are a number of emerging problems with self-pollution due to ineffective cultivation practices and unplanned farm development.

First of all, wastes from the fish and uneaten feed are discharged directly into river, yet water quality monitoring has not been conducted adequately. Farmers do not have any tools for checking water quality (oxygen, pH and temperature), which are essential aquaculture practices.
Secondly, floating cages are densely and spontaneously set by farmers themselves, without planning. This is the most critical survey finding as cage systems are located nearby industrial effl uents and sometimes block the navigation of the river by local vehicles.
More importantly, My Tho City and the My Tho industrial park are not far from production sites, being only 500 m away from some cage clusters. Industrial and domestic wastewater is ultimately diffused along the river’s banks and through the cage culture system.
Although farmers are aware of environmental pollution and take it seriously (78 per cent), they cannot point out the main reason of the deteriorating water quality systematically (42 per cent). The majority of interviewees argued that the industrial development may cause water pollution (58 per cent). Unfortunately, there is no regulation or document on environmental issues relating to cage aquaculture at the local level.
Water quality in the Thoi Son Islet Tilapia cage farming was assessed over three seasons: dry, rainy and transitional seasons. During the dry season, the water quality of TienRiver is better than in the wet and transitional seasons. Most importantly, water quality in the wet season has significantly impacted cage culture production, causing pH, dissolved oxygen, chemical oxygen demand, nitrite, nitrate and phosphate to fall within undesirable levels. The seasonal water quality in the TienRiver (Thoi Son Islet section) can be expressed based on Water Quality Index (WQI) and is depicted in Figure 2.

Seed supply

Seed quality is the most vital concern of farmers, especially for the systems with higher level of intensification. In Thoi Son Islet, fingerlings are purchased from private hatchery providers (Cai Lay, Cai Be and Phu Tuc districts) without the inspection of local Department of Fisheries. There is no evidence to certify that fingerlings are good quality, fully ripe or free from restricted chemicals/drugs. Hence nursery owners do not bear the responsibility for the final products. As a result, the loss rate in the nursery stage of cultivation is very high.

The stocking density of cage farmed tilapia is a significant factor that impacts on the survival, growth and food conversion ratio (FCR). The research survey and findings showed that the average density in Thoi Son Islet cage farms is 8.48 ± 1.83 kg/m3 with average weight of seed is 20.52 ± 8.38 g/fish.
Importantly, there is a linear correlation between stocking density and loss rate and food conversion ratio as shown in Figure 3a and 3b. Practically, high density is not a good practice for caged tilapia to survive and develop. The research findings reveal that there is a relation between the stocking density and: (i) the FCR (r = 0.89, P < 0.01) ; (ii) the loss rate (r = 0.61, P < 0.01).

Feeds and feed management

There are three major components of investment costs for caged tilapia cultivation, including: (i) feed; (ii) seed or fingerlings; and (iii) veterinary including chemicals and drugs. Of these, feed is the highest cost in tilapia cage culture in Thoi Son Islet.

Two kinds of feed used for this system are: (i) manufactured feed; and (ii) home-made feed. The ingredients of home-made feed are various such as rice bran, broken rice and trash fish. Although that kind of feed helps to reduce costs, its protein level is quite low and FCR is rather high.
Feeding practices vary from farmer to farmer. Interestingly, the frequency of feeding may be three or four times a day depending on fish age and farmers’ experience. This leads to overfeeding, and in turn it causes pollution from residue, especially home-made feed. This becomes a critical problem for cage culture as the uneaten feed cannot accumulate on the bottom like in the pond culture to be removed later.
At the study area, feed ratio and FCR cannot be accurately calculated by most of the farmers, who simply feed based on their experience and observed behaviour of the fish. This results in waste and inefficient feeding practices. However, feed input was recorded by a few farmers which the owners themselves did not manage these farms (pointing to financial control rather than good farming practices).
In Thoi Son Islet, the research results show that there is a relation between the FCR and: (i) the loss rate (r = 0.65, P < 0.01); (ii) the productivity (r = -0.54, P < 0.01) as shown in Figure 3. The higher FCR the lower the productivity and higher the loss rate.

Disease issues and health management

Drugs and chemicals are used in most of the steps of the cage culture, such as: hatchery, transportation, cage preparation, stocking, nursing, fingerling and grow-out. There is no residue control on fingerlings, hence the private nurseries do not bear the responsibility for final products. This raises an issue on food quality and safety. Furthermore, most of the farms do not have drug and chemical usage-notes.

The addition of vitamins, amino-acids and probiotic-enzymes are common practices of most farmers in Thoi Son Islet. Moreover, most farmers do not know either the composition of these products nor the concept of withdrawal period. In many cases, products are not in their original packaging and sold in a hand-labelled transparent plastic bag.

Environmental assessment and management

In the tilapia cage farm systems, most cages are located along river banks. The distance between cages is quite close, i.e. typically two to three meters if the cages belong to one owner or five to 10 meters if the cages belong to different owners.
On the other hand, cage locations do not follow the zoning which is encouraged by the government agencies for aquaculture. Thus, their wastes and discharges cause concerns on water quality, diseases, navigation hazards and landscape of the area. These systems also have received negative impacts from other upstream farming activities of the TienRiver. Due to the open culture system, the risk of disease and parasite transfer to wild stocks would be possible.
Furthermore, the practice of farm management is poor. While management standards do not exist or have to be voluntarily implemented by farmers, training and competence of the staff are low and limited. More importantly, no records of monitoring or activities are kept.

Better management practices

Given above context, a spectrum of management practices is required to improve the situation. The practices must be flexible and suitable for small-scale farms to implement. A ‘better management practice’ approach supports fish farmers to limit fish losses, reduce environmental pollution, meet standard requirements of the aquaculture sector, and manage the whole cultivation process through: location planning, cage setting, seed quality assurance, feeding method, water quality and disease control.

Better management practices can include improvements to the cage designs, checking seed quality at stocking, monitoring water quality and fish health, improving bio-security during production, keeping records and a proactive approach to health management. Figure 4 shows the proposed BMPs at Thoi Son Islet.
                 Vietfish International