Recent studies

have predicted that fish consumption in developing and

developed countries will increase by 57 percent and 4 percent,

respectively. Rapid population growth, increasing affluence and

urbanization in developing countries are leading to major changes

in supply and demand for animal protein, from both livestock

and fish. The need for suitable sites has resulted in the cage

aquaculture subsector accessing and expanding into new

untapped open-water culture areas such as lakes, reservoirs, rivers

and coastal brackish and marine offshore water

Divu, D

Philipose, K K

Rao, K Srinivasa

CMFRI Digital Repository

112Handbook on Open Sea Cage CultureFISH GROWTH PARAMETERSAND THEIR MONITORINGD. Divu, K. Srinivasa Rao and K.K.PhiliposeC age aquaculture has grown rapidly during the past decadesand is presently undergoing swift changes in response toincreasing global demand for aquatic products. Recent studieshave predicted that fish consumption in developing anddeveloped countries will increase by 57 percent and 4 percent,respectively. Rapid population growth, increasing affluence andurbanization in developing countries are leading to major changesin supply and demand for animal protein, from both livestockand fish. The need for suitable sites has resulted in the cageaquaculture subsector accessing and expanding into newuntapped open-water culture areas such as lakes, reservoirs, riversand coastal brackish and marine offshore waters.Growth studies are an essential instrument in the managementof fisheries resources since they contribute to estimates ofproduction, stock size, recruitment and mortality of fishpopulations. The study of growth means basically theXIIHandbook on Open Sea Cage Culture113determination of the body size as a function of age. Therefore allstock assessment methods work essentially with age compositiondata. Fish can be aged by examining scales or various bones. Hardbody parts grow as the fish grows, adding annual rings similar tothe rings in trees. Because the growth in the diameter of the hardbody parts is proportional to the growth in length of the fish.Fish growth and feed utilizationGrowth is sensitive to environmental conditions andmeasurements of growth rate can often be used to provide anindex of performance. Slower growth in fishes has been correlatedwith a variety of life history traits – from higher mortality to reducedfood availability and increased age or smaller size at sexual maturity.The health and welfare of a fish can be influenced by a variety ofphysical factors ranging from water quality to territorial defence,unnatural habitats, stocking densities and available nutrition.Stocking density is well publicized as a factor that can influencefish health and growth rate in so far, as overstocking in a systemcan negatively affect water quality and food availability. Often,the stocking density alone or in combination with feeding rate isadjusted by fish farmers to obtain a particular size of fish at harvest,thus indicating that fish growth may be a function of availablewater space.Specific Growth Rate (SGR)The specific growth rate can be calculated based on thefollowing method.SGR= LogeW2 – Loge W1 / D x 100where, ‘W2’ is the mean weight of the fish during the presentsampling, ‘W1’ is the mean weight of the fish during the previoussampling and ‘D’ is the number of days between the twosamplings.Average Daily Growth Rate (ADGR)This can be calculated using the following formula.W2 – W1 / D114Handbook on Open Sea Cage Culturewhere W2 is the final body weight and W1 is the initial bodyweightSurvival rate (SR)SR = (N2 / N1) x 100. The survival rate is always expressed inpercentage, where N2 is the number of survivors during thepresent sampling and N1 is the number of survivors during theprevious sampling.BiomassBiomass can refer to species biomass, which is the mass ofone or more species, or to community biomass, which is themass of all species in the community. The mass can be expressedas the average mass per unit area, or as the total mass in thecommunity. How biomass is measured depends on why it isbeing measured.Biomass = Mean weight x Number of fishesWeight Gain (WG) = Initial body weight - Final bodyweight of fishProtein Efficiency Ratio (PER)PER is the measurement of the body's biological absorptionof a protein from a food source to usable protein. PER is a widelyused method for evaluating the quality of protein in food.PER = Gain in body mass (g) / Protein intake (g)Net Protein Utilization (NPU)The net protein utilization, or NPU, is the ratio of aminoacid converted to proteins to the ratio of amino acids supplied.It is profoundly affected by the level of limiting amino acidswithin the food stuff. As a value, NPU can range from 1 to 0,with a value of 1, indicating 100% utilization of dietary nitrogenas protein and a value of 0 an indication that none of the nitrogensupplied was converted to protein.Handbook on Open Sea Cage Culture115Feed Conversion Ratio (FCR)FCR is calculated from the number of kilos of feed that areused to produce one kilo of whole fish. The ratio of the gain inthe wet body weight of the fish to the amount of feed fed. Thetrue F.C.R includes wasted feed and mortalities. The ratio, usuallyexpressed as a true ratio (i.e. 1 : 1.5) is often quoted as a "rate"(1.5). Two additional terms are used by the farmer, the biologicalFCR and the economic FCR. Biological FCR is the net amountof feed used to produce one kg of fish, while the economic FCRtakes into account all the feed used, meaning that the effects offeed losses and mortalities, for example, are included. Farmsreporting a low FCR normally have good management practicesin place, with no overfeeding and very low, if any, mortalities.Overfeeding or underfeeding will increase the FCR.The basic principle in feeding is that the fish should be fedexactly to satiation. If they are fully fed, the fish are not stressed.In an efficient trout or salmon farm, the FCR will be close to 1.This is extremely low when compared with land animals. Thereare three reasons for this; the biology of the fish, the way the fishlive and the high nutrient concentration of fish feed. Fish have alow body maintenance requirement. Fish are poikilothermic(cold-blooded) animals (their body temperature is equal to thatof its environment) and thus they do not use feed to maintainbody temperature as warm-blooded animals do (e.g. poultry,pigs and cows). For a fish, floating in the water consumes lessenergy than standing and walking on legs. The fishes are veryefficient converters of feed into energy and building blocks(muscles) for growth and their feeds are also more concentratedthan those for pigs or cattle, since they do not need ‘filler’ingredients such as fibres. Fishes use oils and fats as their primeenergy source and, therefore, this is more concentrated than thecarbohydrates needed by land-living animals. Finally, landanimals have a far higher feed capacity than fish and thereforethey can grow well on less concentrated feed.116Handbook on Open Sea Cage CultureFeed EfficiencyA figure used to represent the efficiency of food use. Theinverse of the feed conversion ratio e.g. a feed conversion ratioof 1 : 1.5 becomes a feed efficiency of 0.66 (1 / 1.5).Feed RateThe amount of feed given to the fish, over a specified periodof time . The most common way of expressing this is as percentageof the animal body weight per day. For example a 1000 gramfish, being fed 20g of feed per day would be on a 2% feed rate[(20 / 1000 ) x 100)].Energy AssimilationThe food consumption of fishes can be summarized in thefollowing equation:-C = P + R + F + Uwhere, C = food consumption in energy terms (Joules); P =energy used for tissue growth (including fat deposition, egg andsperm development); R = energy used for work (including bodymaintenance, digestion, activity); F and U = energy losses infaeces and urine respectively. The amount of useful energyavailable to the animal, or assimilation (A) as it is generallytermed, can be derived from A = C - (F + U) = P + R. Assimilationis often quantified in terms of assimilation efficiency.Carrying capacityA major consideration in the site selection process should bethe carrying capacity of the site which indicates the maximumlevel of production that a site might be expected to sustain.Intensive cage fish farming results in the production of wasteswhich can stimulate productivity and alter the abiotic and bioticcharacteristics of the water body, whilst less intensive methodscan result in over cropping of algae and a fall in productivity.Hence profitability or even viability may be seriously affected.Therefore it is extremely important for all concerned with cageHandbook on Open Sea Cage Culture117fish farming to have an accurate evaluation of the sustainablelevels of production at a particular site before culture. The carryingcapacity of a biological species in an environment is thepopulation size of the species that the environment can sustainindefinitely, given the food, habitat, water and other necessitiesavailable in the environment. In ecological terms, the carryingcapacity of an ecosystem is the size of the population that can besupported indefinitely upon the available resources and servicesof that ecosystem. Carrying capacity varies based on a numberof factors, such as, water flow, volume, exchange rate,temperature, oxygen content, pH, size and species of fish beingreared and accumulation of metabolic products. Carryingcapacity is based on loading (the weight of fish per unit of waterflow) and density (the weight of fish per area of water body) ofthe fishes in the system.Condition FactorAn easily measured index of growth is the length-weightrelationship, often referred to as condition factor (C). C is theratio of fish weight to the length cubed. Condition factor, oneof the most important feeding and growth criteria. Since ‘C’may vary between species, strains, diet and feeding levels, waterquality and hatchery management, it should be calculated foreach hatchery. ‘C’ is calculated by weighing a sample of 50-100fish together. After the average weight and the average lengthare measured, values are used in the formula C=W/L3. A highcondition factor would indicate a well-fed fish, while a lowcondition factor may indicate a poorly fed fish of the same length.

Fish growth parameters and their monitoring

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Fish growth parameters and their monitoring

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