A & B RAS AGRO INDUSTRY

Water Quality: Ammonia Ammonia exists in two species: un-ionized ammonia (NH 3 ) and ionized ammonium (NH 4 + ), the amount of each type depending on the pH and temperature of the water. At a lower pH, the excess hydroniums (H + ) in the water tend to drive the balance toward ammonium. At a higher pH, the lack of hydroniums tends to produce un-ionized ammonia. Temperature has a lesser effect, with the amount of un-ionized ammonia increasing with increasing temperature at any given pH. This is of more than academic interest to aquaculturists, since only the un-ionized form is toxic. So, the total ammonia (ionized and un-ionized combined) that is measured by water quality analysis must be evaluated in light of pH and temperature. The generally accepted rule of thumb is that un-ionized ammonia in excess of 0.02 mg/L is potentially toxic, though this may vary slightly with species of fish. The un-ionized ammonia calculator below can be used to determine the toxicity of an...

Water Quality: Buffering t Is All about the Carbon Cycle The interplay between the carbon-based life on earth with the physical biosphere results in the profoundly important carbon cycle, which is responsible for everything from the earth's food supply to free oxygen in the atmosphere to global warming. One aspect of the carbon cycle that is of paramount importance to fish is the relationship between inorganic carbon and water. The vast majority of carbon on earth (six times more than the carbon in all the organic matter, living and dead, including fossil fuels) resides in the earth's water in the form of carbonates (carbon/oxygen compounds). These form the basis of the carbonate buffering system, which is the key to successful fish life. As explained in an earlier chapter,  ( 3. Water Quality: Gases ) oxygen (and nitrogen for that matter) can dissolve in water and the amount of these gases in water is a matter of partial pressure and solubility. Carbo...

Water Quality: Gases Understanding Oxygen in Water The concept of partial pressure was introduced in the last chapter. To fully understand how oxygen moves into a recirculation system we need to take this further. Gas pressure can be expressed in several ways. The pressure of the atmosphere on the ocean's surface (or your lungs if you are standing on the beach) is about 15 lbs/in 2  (100  kPa ) which is termed one atmosphere (A). If you fill a glass tube having one closed end with a fluid and immerse the open end into an open container of the fluid, the fluid will fall in the tube and pull a vacuum until the atmospheric pressure pushing it back up equals the weight of the column of fluid. This is a barometer. The level of fluid will vary slightly as the total air pressure varies. Mercury is commonly used as the fluid. Standard air pressure at sea level will support a 760 mm (29.9 inch) column of mercury (in physiology, mmHg is the common unit of gas pressure, m...

Fish Metabolism Understanding How Fish Breathe In order to successfully design and operate a life support system for fish, one must have a basic understanding of the physiological requirements of fish.  Fish use the oxygen dissolved in the water for respiration. This dissolved oxygen (DO) is gas in simple solution (not the  covalently  bound oxygen in the water molecule). Fish extract this oxygen with their gills. Water has relatively little DO (<14 mg/L) compared to the oxygen (240 mg/L) in air, so fish must be efficient in getting it. One factor that contributes to this efficiency is the unidirectional flow of water through their gills.  Terrestrial  animals have bidirectional flow (in and out of the same tube, the trachea) which is inefficient in that fresh inspired air mixes with stale expired air. With unidirectional flow, there is no mixing. Another factor is the  countercurrent  movement of blood and water. At the  lamell...

Introduction Why Recirculation Aquaculture? The need for high quality human food grows as the world's population grows. Most of the world's wild fish populations are now at or beyond maximum sustained yield, meaning that additional harvest only reduces the fish available for next year's catch. In addition, there is concern that wild caught fish may sometimes be contaminated with mercury or other pollutants.   Aquaculture   is seen as a way to produce more fish from a controlled environment. However, traditional extensive aquaculture (ponds, raceways) requires an abundant water supply. The same human pressures that increase the demand for fish also decrease the water available to grow them in. All of these factors encourage the use of recirculation aquaculture, where a large amount of high quality fish can be grown in a small amount of water. The engineering and biology behind recirculation aquaculture is well established and you will learn the details of these in th...

মাছের রোগব্যাধি ও প্রতিকার- শীতকালীন মাছের ক্ষতরোগ: শীতকালে মাছের রোগ-বালাই বেশি হয়ে থাকে। যার কারণে খামারিরা অর্থনৈতিকভাবে ক্ষতির শিকার হয়। দূষিত পানি বা পানির চেয়ে মাছ বেশি হলে উপযুক্ত খাবারের অভাব, পানির তাপমাত্রা, ক্ষারকতা বা অমস্নত্বের অত্যধিক হ্রাস বৃদ্ধি হয়, এছাড়া পরজীবী ও জীবাণুর আক্রমণে শীতকালে মাছের শরীরে রোগ দেখা দেয়।  রোগাক্রান্ত মাছের কিছু অস্বাভাবিক আচরণ ও শারীরিক অসঙ্গতি দেখা যায় যেমন- খাবারের প্রতি অনিহা, কঠিন বস্তুতে গা ঘর্ষণ, চলার গতি ধীর হওয়া; পানির উপর ভেসে থাকা; লাফালাফি করা; এছাড়াও দেহের যেকোনা অংশে ঘা হতে পারে। রূপালি রঙের সাদা ফোঁসকা উঠে পেট ফুলে যাওয়া, ফুলকা ফুলে উঠে এবং গায়ে আঠাঁলো বিজলা বের হওয়া। আমাদের দেশে শীতকালে সাধারণত ক্ষত নামক রোগ মহামারী আকারে দেখা দেয়। উপযুক্ত ব্যবস্থা না নিলে এসময় খমারিরা দারুণভাবে ক্ষতিগ্রস্ত হয়। কারণ, লক্ষণ, প্রতিকার ও চিকিৎসা: একানোমাইসিস নামের একপ্রকার ব্যকটেরিয়ার কারণে মাছের ক্ষত রোগ হয়। এ রোগের জীবাণু সম্পর্কে দ্বিমত থাকলেও প্রতিকূল পারিপার্শ্বিতা এ রোগের মূল কারণ বলে মৎস্য বিজ্ঞানীরা মনে করেন...