Basics Flashcards

Question

Intestinal transit time

Answer 1

▪ Varies with diet composition, meal size and feed structure ▪ Increased flow of digestible carbohydrates, proteins and lipids (elicit the strongest signal) into the distal regions of the small intestine inhibits intestinal motility ▪ Soluble fibre and bulking agents often reduce nutrient digestibility, particularly dietary lipids ▪ Insoluble fibre can speed up passage rate ▪ Intestinal passage rate is expected to vary among fish species (comparative studies are not available) ▪ In trout and Sea bass, marked feces were observed between 5 to 35 hours after the meal

Answer 2

▪ The number of bacteria in fish digestive tract is lower than in homoeothermic animals → great differences among fish species (herbivorous > carnivorous) ▪ Microbes secrete enzymes able to hydrolyse and metabolise protein, starch, cellulose, chitin and lignin ▪ Higher concentrations of bacteria are present in the distal compartments. Feed sources and microbiota of the environment have a great impact on intestinal microbiota ▪ The products of bacterial fermentation of dietary nutrients are amino acids, glucose, acetate, propionate and butyrate → can be absorbed efficiently ▪ The quantitative contribution from microbial fermentation to total nutrient supply remains small

Answer 3

▪ Products of the action of digestive enzymes can enter the organism across the brush border by diffusion or facilitate transport (down a concentration gradient) or by active energy-dependent transport (against a concentration gradient)

Answer 4

▪ Fish have the apparatus for nutrient absorption all along the intestinal tract (in most fish the absorption rate decreased toward the distal segments) ▪ Active transporters are generally dependent on ions such as Na+, Cl, K+ or H+ → energy is needed to maintain ion gradient across the cell membrane ▪ Transporters capacity tends to increase with increasing water temperature

Answer 5

vedi slide 42

Answer 6

vd slide 43

Answer 7

▪ The experimental design must consider many factors: species, culture, diet design, sample and data collection, chemical analysis, and data analysis. → developed in conjunction with the testing of a defined and testable hypothesis ▪ The use of experimental protocols is essential to obtain results comparable with those of other studies ▪ The aim of experimental design is to minimize variation attributed to experimental error

Answer 8

→ WATER: may limit observation and adversely affect the integrity of feed and nutrients; may provide nutrients (minerals and planktonic organisms); quality conditions must be maintained throughout the experiment

Answer 9

A variety of culture systems can be used → flow-through, recirculating, semi- recirculating, static → each has shortcomings: ➢ Non continuous flow systems require careful management of water quality → the accumulation of metabolites may reduce growth or affect response variables → routine replacement of water may disturb the fish and affect response variables ➢ Recirculating systems need appropriate biological and physical filters → WARNING: metabolite and particulate material accumulation ➢ Flow-through systems need to be managed to maintain stable water quality conditions An ideally design culture system isolates replicates from one another → reduced risk of contamination ▪ The volume of the experimental units (tanks in general) must be chosen according to the predicted final biomass ▪ Individual units that compose an experimental system are the units of observation for the statistical analysis → the assumption is that each unit of observation is independent ▪ The number of organisms in each unit depend on the species investigated and must be contained to limit hierarchical feeding behaviour ▪ If the organisms can be individually identified their individual responses can be measured ▪ If the weight of each organism for each treatment is recorded at different times a growth rate exponential (GRE) can be determined → WARNING: repeated weighing can cause stress and mortality

Answer 10

▪ Source, strain, age, previous nutritional history and condition of the fish can influence responses in nutritional studies ▪ Experimental organisms derived from a single mating (full sibs) or several matings can be used → in the second case proportional representation among treatments should be adopted

Answer 11

Research studies often used basal diets that consist of refined ingredients (semi-purified diets) with defined chemical compositions → for some species, feed intake and growth may be negatively affected by semi-purified diets → a reference diet of known chemical composition and demonstrated ability to support normal growth a target species is recommended ▪ Once prepared, diets should be storage under conditions (frozen) that maintain the freshness for the duration of the experiment → small quantities of diet can be stored at 4°C before feeding ▪ Before the beginning of the trial, the diets should be analysed to confirm that the targeted nutrients levels were achieved

Answer 12

A sufficient number of treatments formulated to contain graded amount of the nutrient investigated and sufficient or excessive levels of the other nutrients should be used: ➢ A basal diet provides a baseline level for evaluation of the response variables ➢ The other diets should cover a wide range of concentration of the target nutrient ➢ The total number of treatments is at least 5

Answer 13

▪ Experimental organisms are fed at rates approaching apparent satiation to ensure maximum growth ▪ To an accurate calculation of feed utilisation the amount of uneaten feed must be minimized → conversely uneaten feed should be recorded ▪ The optimal number of meals can be species- or life-stage specific → young and rapidly growing organisms benefit from being fed several times ▪ The experiment should not begin until the organisms have consumed the same diet for a period of time (at least 15-20 days) → conditioning or transit diets could be used ▪ For rapidly growing organisms, observed changes in weight gain of up to 1000% (10 x) are recommended → for larger organisms an increase of 200- 300% (2-3 x) may be acceptable → a standard often used 300% increase in body weight

Answer 14

▪ The time required to observe the recommended weight increases depends on the rate of the response to the nutrient under investigation and the temperature of the water → WARNING: avoid the prematurely termination of the experiment ▪ The duration of nutritional trials normally encompasses at least 8-12 weeks → it is not appropriate to arbitrarily assign a specific time period

Answer 15

▪ Growth is the most commonly used response to evaluate modification to the dietary content of a nutrient ▪ The growth of aquatic organisms depends on life stage, strain, environmental conditions and nutrient intake → can be measured as a change in weight (commonly) or length (less frequently)

Answer 16

𝑀𝑒𝑎𝑛 𝑤𝑒𝑖𝑔ℎ𝑡 = 𝑡𝑜𝑡𝑎𝑙 𝑏𝑖𝑜𝑚𝑎𝑠𝑠 𝑜𝑓 𝑎𝑛𝑖𝑚𝑎𝑙𝑠 ÷ 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑎𝑛𝑖𝑚𝑎𝑙𝑠 𝑊𝑒𝑖𝑔ℎ𝑡 𝑔𝑎𝑖𝑛 = 𝑊𝑡 − 𝑊0 𝑃𝑒𝑟𝑐𝑒𝑛𝑡 𝑤𝑒𝑖𝑔ℎ𝑡 𝑔𝑎𝑖𝑛 = (𝑊𝑡 − 𝑊0 ÷ 𝑊0) × 100 𝑆𝑝𝑒𝑐𝑖𝑓𝑖𝑐 𝑔𝑟𝑜𝑤𝑡ℎ 𝑟𝑎𝑡𝑒 𝑆𝐺𝑅 = ((ln 𝑊𝑡− ln 𝑊0) ÷ 𝐷) × 100 Growth rates should be reported based on a model that fits the response of the specific stage of the organisms → larval growth is exponential → SGR is an appropriate measure → in other life stages the exponential function is not suitable

Answer 17

𝑇𝐺𝐶 = (𝐹𝐵𝑊^ (1/3) − 𝐼𝐵𝑊^ (1/3)) ÷ sum (𝑇 × 𝐷) × 100 𝑃𝐹𝐵𝑊 = (𝐼𝐵𝑊^ (1/3) + sum (𝑇𝐶𝐺 ÷ 100 × 𝑇 × 𝐷))^3 FBW = final body weight (g/fish) IBW = initial body weight (g/fish) PFBW = predicted final body weight (g/fish) D = duration of the period (days) T = water temperature (°C)

Answer 18

TGC represents the growth curves of different species (e.g. Rainbow trout, Chinook salmon, Atlantic salmon) in a wide range of water temperature → systematic errors may arise when T moves far away from the optimum ▪ TGC values and growth rates are dependent on species, genetics, nutrition, environment, husbandry and other factors ▪ FCR and feed efficiency are quantitative measures of efficiency but semi- descriptive → the nutrient composition of weight gain and feed may vary

Answer 19

The proximate composition of the whole body measured at the beginning and at the end of the trial allows accurate estimation of the effects of the dietary treatment % 𝑟𝑒𝑡𝑒𝑛𝑡𝑖𝑜𝑛 = (𝑊𝑡 × 𝑁𝑡 − 𝑊0 × 𝑁0) × 100 ÷ 𝑁𝑖 Nt = final nutrient content N0 = initial nutrient content Ni = nutrient intake

Answer 20

▪ Animals seek to eat an amount of balanced feed to follow a determined growth path → maximal protein accretion and carcass lean growth rate determine nutrient requirements for growth ▪ Estimation of nutrient requirements is affected by the selected response parameters → the requirements to maximise protein gain is higher than that required to maximise weight gain ▪ Weight gain and protein deposition are poor indicators for the estimation of micronutrients (minerals) requirements → the whole-body retention of the micronutrient is better ▪ Data obtained in long-term studies remain an important way to determine a dietary requirement for trace elements