Fish & Invertebrate Nutrition Flashcards
1
Q
What do we know about the nutrition of fish?
What is the general nutrition strategy of most fish?
What species are herbivorous?
What species are detritivorous?
What is the general calculation for metabolic rate?
A
Natural History
- Essential nutrients = protein, lipid, carbohydrates including fiber, vitamins and minerals
- Most info on nutrition for those cultured for food where goal is rapid growth and efficient production
- Little info on fish spp kept in zoos and aquaria
Wild diet and Foraging Ecology
- Fish can be grouped into carnivore, omnivore, herbivore and detritivore, but these can vary widely.
- Most fish are primarily carnivorous or omnivorus with ~5% herbivores
- Carnivory – all elasmobranch and some bony fish (often plegic and ambush predators
- Omnivore – common in bony fish
- Herbivorous – include both freshwater and marine bony fish that consume plans, micro and macroalgae, detritus and even wood in some catfish species
- Parrotfish (Scaridae), some tilapia (Oreochromis and Tilapia spp)
- Detritivorous fish – mullet (Mugilidae), some surgeonfish (Acanthuridae) and some aquaculture spp (smallscale yellowfin – Plagiognathops microlepis)
- Important to understand the types of food eaten in the wild, feeding patterns and seasonal changes in the diet to determine diet for human care.
Metabolism and Energetics
- Metabolic weight defined as bodyweight in Kg^0.80
- Smaller fish need higher percentage of BW than larger fish
- Activity level (feeding, breeding, changes in water flow) and water temperature affect energetic requirements (increased energy expenditure with increasing water temp).
- Few energetic requirement equations available, and differences based on species, body size, activity level, and water temperature.
- Feed to appropriate BCS
2
Q
Describe the GI anatomy of fish and how it relates to digestion.
What species are stomachless? Does this affect their nutritional strategy?
What is the role of the pyloric ceca? What fish are these better developed in?
What fish have a spiral valve?
Do teleosts or elasmobranchs have slower transit times?
Where do herbivorous fish get their energy from?
A
Anatomy and Digestion
- Stomach in most species is simple sac but there is no stomach in jawless fish (hagfish and lamprey (Agnatha)), and members of the families Cyprinidae (goldfish, carp, koi), Labridae (wrasses) and Gobiidae (gobies).
- Stomachless fish can be carnivores, omnivores, herbivores and detritivores
- Carnivorous fish have shorter intestines than herbivores
- Many have pyloric caeca – diverticula of the intestine at the posterior end of the stomach that secrete digestive enzymes and increase absorptive SA.
- Better developed in carnivorous fish
- Elasmobranchs and non-teleost ray-finned fish (bowfin, gar, sturgeon, and lungfish) have a spiral valve, which increases the absorptive surface area.
- Gut passage rates in fish are dependent on species, animal size, gut morphology, temperature, food type, meal size, and feeding rate
- Elasmobranch slower GI transit than similarly sized teleost carnivores
- Assimilation efficiency is how efficiency animals convert ingested food into energy - high in adult fish and wider range in larval fish
- Food type, ration size, and gut morphology likely play a role in some of these differences
- Information on gut microflora and microbial enzyme activity in fish GI tracts is lacking.
- Microbial fermentation in the hindgut is an important source of energy in marine herbivorous fish
3
Q
What are the main sources of energy utilized by fish?
How well do they use protein, carbohydrates, and lipids?
What is gross energy?
What is metabolizable energy?
A
Nutrient Requirements
- All fish require same nutrients at a cellular level and fish can accumulate some nutrients (minerals) directly from the water
- Sources of energy
- Energy obtained from metabolism of protein, lipid and carbohydrates
- Fish are more efficient at using protein as an energy source than birds or mammals since ammonia synthesis does not require energy.
- Carbohydrates may serve as energy source via endogenous metabolism (absorbed glucose) or microbial fermentation producing VFAs
- Carbohydrates less preferred as an energy source for carnivores (compared to omnivore/herbivore) and marine fish (compared to freshwater fish)
-
Lipids are often a preferred energy source in commercial fish feeds due to cost and efficient use by fish.
- Can improve growth efficiency in aquaculture, but excessive energy relative to protein can reduce total feed intake (limits intake of essential nutrients) and increases body lipid deposition
- Gross energy – total energy released upon combustion of a food item, but does not represent amount of energy available to the animals. GE of lipid > protein > carbs.
- Digestible energy - energy in food minus amount of energy excreted in feces (~20% less than GE)
- Metabolizable energy – digestible energy of a food minus the energy to excrete any waste pdts via urinary and gill loss (~5% less than DE)
4
Q
Describe the protein reqruiements of fish.
What are two important essential ammino acids for fish?
What amino acid in excess hindered growth in Nile tilapia?
What source of protein most closely matches the nutrient requirements of fish?
A
Protein
- 10 essential amino acids cannot be produced by fish.
- Arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine
- Arginine has high requirements due to low activity of urea cycle enzymes
- Taurine is essential for larval fish
- Ratio of required AA proportional to optimal dietary protein level
- This was determined with goal of weight gain
- Recent study in Nile tilapia - lowering histidine below previously published requirements improved weight gain, muscle fiber quality, and efficiency of protein utilization
- Dietary sources must provide essential AA and additional nitrogen (to synthesize AA)
- Require ~30% digestible protein in fast growing aquaculture spp, unknown for zoo/aquaria
- Free AA important in larval fish – lack enzymes to digest intact protein
-
Fish based protein sources closely match nutritional requirements
- Terrestrial animal protein sources – lack some essential fatty acids and high in fat
- Plant protein sources – lack many essential amino acids and may contain anti-nutritional factors
- Ratio of protein: energy important as AA serve as energy precursors in fish
- For most species, optimal ratio is ~90 g/Mcal
- Nitrogenous waste can be minimized by providing optimal levels of amino acids and reducing digestible protein:energy ratio such that nitrogen retention efficiency is high
5
Q
What are the nutritional lipid requirements of fish?
What are the essential lipids? Which one do young fish require in high levels?
What fatty acids have been found to play an important role in development?
A
Lipid
- Levels from 10-20% dry weight of diet (higher for juveniles than adults)
- Excessive fat can lead to fatty infiltration of the liver
- Essential lipids – cholesterol, phospholipids, inositol, and fatty acids
- Dietary phospholipid inclusion can improve survival and growth in larval and juvenile fish
- Inositol component of cell membranes which can be synthesized endogenously but often not at high enough levels to meet needs – young fish (esp larvae) require higher levels. Fishmeal and fish have high inositol.
-
Fatty acids are preferred energy source in fish – role in larval development, maintaining cell membranes and modulating immune responses
- Require linoleic acid (omega 6) and linolenic acid (omega 3)
- Many carnivorous and benthivores marine fish require long chain omega 3 PUFA and higher omega 3:omega 6 ratios.
- Cold water spp higher requirements for omega 3 PUFAs than warm water
- Omega 3 PUFA found in fish meal and fish oil, also in algae
- Arachidonic acid shown to improve egg quality and survival, larval growth and survival and adaptation to different salinities
6
Q
What are the carbohydrate requirements of fish?
How well do they digest carbohydrates?
What dietary strategy utilizes these the best? Which is the worst?
A
Carbohydrates
- Sugars, starches, and fiber – poorly digested by most fish
- Largest role in nutrition of herbivorous fish
- Cold water carnivorous fish have lowest capacity to digest starch, while warm water herbivores or omnivores are more capable
- Improve digestibility with heat and pressure – gelatinization
- Limit starch where practical, especially in cold water carnivorous fish
- Non-starch polysaccharides – indigestible by fish and can impair nutrient absorption
- Fermentable carbs important in caudal GI tract in herbivorous, omnivorous, and planktivorous fish
- likely that most of the carbohydrates used for microbial fermentation are hemicellulose and cellulose
- Microbial communities in GI likely critical for proper health and nutrition
7
Q
What are the vitamin requirements of fish?
Deficiencies of vitamin A in larval fish result in what abnormalities?
What carotenoids can fish use that mammals and birds cannot?
Vitamin D toxicity results in what deformities?
Can fish synthesize vitamin C?
What are the signs of vitamin c deficiency?
Why does thiamine need to be supplemented?
What is the role of choline?
A
- Vitamins
- Serve as cofactors, hormone and regulators of cellular differentiation.
- Required in trace amounts
- Fat soluble – A, D, E, K vs. water soluble (Vit B and C, choline)
- May be supplemented but greater risk of toxicity since they are stores in liver and adipose
- Vit A – involved in cellular differentiation and vision. Deficiency in larval fish associated with incomplete eye migration, abnormal pigmentation, and skeletal abnormalities. In juveniles, skin and liver hemorrhage, exophthalmos, and twisted gill opercula have been described
- Carotenoids (pro-vit A compounds) less toxic since conversion is regulated
- Astaxanthin and canthaxanthin are carotenoids which fish can convert to vitamin A. Most birds and mammals cannot convert theses to Vit A
- Carotenoids (pro-vit A compounds) less toxic since conversion is regulated
- Vit D – calcium homeostasis and development of skeletal tissues and cellular differentiation.
- Sourced form plants (ergocalciferol – D2) and animal (cholecalciferol (D3). D3 much more effective than D2.
- Laval fish have higher requirement but toxicity can result in vertebral deformities
- Vit E – Alpha-tocopherol more biologically active. Serve as antioxidants to stabilize membranes, affect eicosanoid signaling and cellular proliferation and modulate immune responses.
- Dependent on levels of other antioxidants (Vit C) to be effective
- Nutrient requirements often described in relation to the PUFA content – high PUFA content in fish diets
- Often require higher levels for antioxidant/immune function effects, and commercial larval fish feeds may need higher Vit E due to large surface area, higher risk of lipid peroxidation, and high level of omega 3 PUFAs
- Water soluble vitamins have lower risk of toxicity and are often supplemented at high levels
- Some cartilaginous fish can synthesize vit C, but unknown if it is in enough quantity.
- Supplemental vit C improved immune responses so recommended to supplement for all fish.
- Higher doses needed for improvement in immune function (antibody production, complement activity and survival after disease)
- Signs of vit c deficiency: lordosis, scoliosis, cartilage and collagen defect, petechial hemorrhaging, and fractures of spine.
- Thiamine (B1) is of concern in any fish eating species – thiaminases in fish tissues activated at death. High thiaminase in alewives, caplin, cyprinids (feeder goldfish)
- Any frozen/thawed fish should be supplemented
- Pyridoxine (B6) may be needed for larval development
- Choline – vitamin like nutrient and component of phospholipid and precursors of neurotransmitter acetylcholine
- Most fish cannot synthesize and supplementing may also reduce excessive lipid accumulation and development of fatty liver
8
Q
Describe the mineral requirements of fish.
Which minerals can be acquired from the water?
What is the usable form of iodine in the water? What water quality parameters may reduce its bioavailability?
A
Minerals
- Macrominerals – Ca, P, Na, K, Mg
- Trace minerals – Cu, Zn, Fe, Mo
- Ultra trace minerals – I, Co, Cr, Mo
-
Some minerals (Ca, Cu, Fe, K, Mg, Na, Se and Zn) acquired from water
- Ca, K, Mg and Na met by the water but low pH restricts absorption
- Phosphorus may be present from plant, animal or chemical sources and dietary source is required
- Plant based forms often low bioavailability and may complex with other nutrients
- Selenium involved in antioxidant and housekeeping functions.
- Aquarium food items often contain lower levels. Selenium can also be toxic and result in reduced growth rates, mortality and renal calcinosis
-
Iodine – functions as component of thyroid hormones
- Deficiency is common cause of goiter in elasmobranchs
- Ozone reduces bioavailability – the usable iodide is oxidized to unavailable iodate. High nitrate also reduces iodide uptake
9
Q
Describe the various food items used to feed fish.
Why are fish based diets recommended?
What are the side affected of undigested feed?
What are the benefits of pellets, flakes, and gel diets?
What fish should not be fed to bottom foraging species?
When are live foods needed? How can their nutrient profiles be improved?
How do vitamin and mineral supplements need to be administered?
A
Feeding
- Diet selection and Formulation
- Diet should be palatable, free from contamination and of sufficient quantity and quality. Should mimic wild diets and provide variety and enrichment. Consider species, life stage, body condition, reproductive state and/or disease state
- Food Types
- Typical diet involves commercial pellet and flake, gel diet, harvested fish/inverts, plants and algae and live foods
-
Animal (fish) based diets often show higher digestibility and better fatty acid and protein profiles, but concern for cost, high fat, and sustainability
- Plant based diet contain anti-nutritional factors that can reduce digestibility and impair health
-
Undigested feed negatively impacts water quality – Nitrogen of greater concern in saltwater vs phosphorus in freshwater, both essential for algal growth
- Improving food type can reduce environmental impacts – nitrogenous wastes minimized by providing optimal levels of amino acids and reducing digestible protein:energy ratio
- Phosphorus waste may be from variable P digestibility or phytate-bound P from plant based ingredients
- Improving food type can reduce environmental impacts – nitrogenous wastes minimized by providing optimal levels of amino acids and reducing digestible protein:energy ratio
- Pellet and flake foods
- Formulated with mix of animal and plant based ingredients and nutrient levels formulated to meet or exceed known requirements. Formulated to fish feeding strategy/position in water column.
- Gel diet
- High protein level, high moisture level thus higher palatability than dry diets. Easy to enhance with supplements/oral medications. Generally sink.
- Harvested fish and invertebrates
- Fatty fish (herring, mackerel, sprat) should not be fed to macroinvertebrate or bottom foraging species (dasyatid rays). Should be of quality for human consumption.
- Essential FA and ratio of omega 3:6 FA differs between freshwater and marine fish due to phytoplankton source – only feed freshwater based food to freshwater fish and marine based to marine fish.
- Avoid feeding herbivorous fish a diet containing seafood – exceeds protein and lipid requirements, fat deposition in muscle, coelomic organs and liver
- Plants and algae
- Live plants can provide supplemental source of nutrition for herbivorous fish
- Microalgae (phytoplankton) used in marine herbivores, marine fish larvae, and fingerlings.
- Can have high fraction of beta glucan, a potential immune stimulant
- Variation in chemical composition depending on species and growth conditions
- Can feed directly, add to commercial feeds or gut loaded to an intermediate source (rotifers)
- Macroalgae (seaweeds) are also used as fish feed
- Number of benefits of incorporating algae into fish diets, but has limited digestibility in non-herbivorous species due to the cell wall. Can reduce growth if too much added to non-herbivorous species to meet growth requirements
- Live foods
-
Ambush and visual predatory fish (frogfish, seahorses) often require live food to trigger eating response. Most larval fish require in early stages of development
- Brine shrimp (Artemia) for brackish/marine and rotifers (brachionus) for freshwater, brackish or marine
- Brine shrimp are nonspecific feeders and as long as food is small, variety can be fed (algae, microparticles, omega-yeast, marine oil emulsion). Typically obtained as cysts or live cultures reared in salt water.
- Rotifers obtained as cysts or live cultures and maintained in freshwater or brackish water (some can be salt water). Recommended to gutload or do supplemental feedings before feeding.
- Live foods should be housed to meet behavioral and physiological needs
- Without good feeding practices, many live foods are nutritionally incomplete. Gut loading can further increase nutrient value
- Gut loading refers to the diet provided for a specific period prior to feeding out with nutrients designed to fill the GI tract rather than be absorbed.
- Can carry infectious disease – culture in house and quarantine prior to feeding out
-
Ambush and visual predatory fish (frogfish, seahorses) often require live food to trigger eating response. Most larval fish require in early stages of development
- Vitamin and Mineral Supplementation
- Variation recommended to minimize risk of deficiencies
-
Liquid supplements can leach away before consumption, be removed by filtration or negatively impact water quality.
- Capsules/tablets more reliable
- Many are unstable in light, heat, oxygen or water so careful storage needed
- Feeding portion of total diet as high quality pellet, flake or gel may help ensure delivery of vitamins/minerals since these are formulated in stable mixtures
10
Q
How often should fish be fed?
What amount is a good starting point?
Describe the body condition scoring of koi, stingrays, and reef sharks.
A
- Feeding behavior, amount, and frequency
- Numerous factors (how diet presented, composition, hormonal/biological state, environmental conditions, fish health and developmental state and system design) affect food intake
- Food items should be small enough to be ingested while large enough to be consumed without expending too much energy
- Feed requirements vary with diet, species, life history stage (juveniles > adults), water quality (temp and salinity), exercise level and habitat size, and social interactions (dominance hierarchy).
- Adult bony fish 0.5-1% BW/day is good starting point
- Reduce if not consumed w/I 5 mins for an individual or 15 minutes for animals in large groups
- Feeding amounts should be adjusted by growth data, BW, body condition comparison with wild counterparts and bloodwork
- Increase in ammonia or seeing food is sign of overfeeding
- Body condition
- Often use 5 point scale
- Best assessed by a group of people and useful when compared across a group or across time, especially during physiologic change (breeding/growth)
11
Q
Describe the fish food storage, preparation, and quality control.
How can oxidation and thiaminase activity be minimized?
What is the typical discard date for frozen seafood?
What conditions are needed for storing fruits and veggies? What about dry foods?
What is the proper method for thawing seafood?
What should the fish look like?
How is quality control ensured?
A
Food storage and preparation
- Ensure free of contamination and stored, thawed, prepared and fed in a manner that preserves nutritional quality
- Food safety and monitoring
- Hazard analysis and critical control point program applied to help to ensure food safety – each facility and vendor should develop their own HACCP program
- Identify potential hazards/risks within the system, identify control points, establish critical limits, establish monitoring, establish corrective measures and develop record keeping and verification methods
- Hazard analysis and critical control point program applied to help to ensure food safety – each facility and vendor should develop their own HACCP program
Storage
- Temperature, humidity, air exposure, and lighting all affect food quality
- Frozen food stored between -22 and 0 F to minimize oxidation and thiaminase activity
- Refrigeration at < 39F should be used for storing vegetables, fruit, forage and short term (< 24hr) holding of thawed seafood and gel foods
- Room temperature (64-70F) and 50-60% humidity can be used for some dry foods
- Food should be off the ground and room well ventilated
- Can store in sealed containers to minimize air and light exposure
-
For frozen seafood, discard date should be < 12 months from catch.
- Reduced to 6 mo for high fat foods (mackerel and herring)
Food preparation
- Wash hands before putting on gloves, and wash gloves, knives, cutting boards, and other utensils between food types to prevent cross contamination
- Must clean (soap and water) and sanitize (high heat dishwasher >160F, or chemically) all utensils and containers
- Seafood - Thawing of seafood should always be done in air under refrigeration at <39F
- Incorrect thawing can result in nutrient loss, fat rancidity, microbial buildup and loss of palatability.
- Fish should have bright red gills, clear corneas, firm elastic flesh without breaks
- All thawed seafood kept iced or refrigerated and used within 24 hr. Never refreeze
- Produce – wash vegetables and produce and inspect for damage/pests
- Pelleted/flake food – inspect for foreign material, mold, pests
- Gel food – once made, store and handle as if raw foods. Ensure temperature of water to mix appropriate to inactivate microorganisms.
Quality Control
- Frozen or fresh fish should be analyzed to monitor the fluctuations in nutrients that can occur on a seasonal, regional, or species-specific basis
- Schedule for sampling and analysis should be made for all feed types (dry food too).
- Analyses should include composition of moisture (or dry matter), crude protein, fiber (more for plant-based or commercial food items as seafood is generally low in fiber), gross energy, macrominerals, trace minerals, and vitamins
- Submit in the exact manner that it is offered to the animal (supplements added)
12
Q
Describe the nutritional support of sick fish
What factors of the food encourages consumption?
What are some appetite deterrents? Are there any potential appetite stimulants?
Describe assist feeding. Are there any potential risks?
A
Nutritional support
- Changes in feeding frequency or amount may indicate inappropriate feed, environmental conditions or disease
-
Appetite stimulants – fish primarily detect food through olfaction and sight, but appearance, feel and taste are key factors in determining whether food will be consumed
- Poor quality feeds may contain deterrents such as oxidized oils, trimethylamine (produced in decaying fish flesh) and aflatoxins (produced by mold) which can happen with improper storage
- Garlic may have some potential though scare literature on its effectiveness. High doses can lead to oxidative damage
- Assisted feeding
- Some species have normal periods of inappetence – moray eels (2-6 months)
- Can make prior diet into a slurry – put through strainer so it is smooth
- 60:40 food to water ratio
- Start 0.5-1% and increase to 2-3% as necessary
- Approximate length from mouth to middle of pectoral fins
- GI rupture or accidental administration into the swim bladder in physostomous fish are potential adverse effects
- Force feeding – medium to large fish, whole or cut seafood can be force fed
13
Q
Describe the nutrition of larval fish.
How quickly do fish grow?
How long do they rely on their yolk sac?
What is the typical diet for a larval fish?
A
Larval and Boodstock nutrition
- Larval fish grow rapidly -30-100% growth/day
- Egg lipid levels positively correlate with incubation times . Larval fish depend on yolk sac for 3-5d post-hatch but may last up to 60d in some species
- Recommended to offer food while yolk sac still available
- Typically fed brine shrimp nauplii and rotifers. Some commercial microparticulate diets available with hydrolyzed protein (don’t possess anatomy/physiology to breakdown complex food particles). Always enrich live foods prior to feeding,
- Broodstock nutrition, especially vit E and tryptophan for several weeks to months beforehand is important for hatch success
- In fish species with parental care, energy requirements likely increased despite often a reduction in food intake. Supplement during this period.
14
Q
Describe goiters in fish.
How do they appear in teleosts versus elasmobranchs?
What are the three forms of iodine? Which is the usable form?
What are some causes of low iodine in the water?
What are some important differentials to consider?
How can this be diagnosed? What levels should be in the water?
How can it be treated?
What are the recommended preventatives?
A
- Thyroid Hyperplasia (Goiters) - CGFM
- Mass effect in opercular cavity (teleosts) or ventral gular mass (elasmos)
- Cause - low iodide or dissolved organic iodine in teh water or diet → oxidation to iodate, which is not available to fish
- Etiology
- In bony fish the thyroid is diffuse, tissue mainly in oropharynx submucosa
- In elasmos, thyroid is distinct, encapsulated organ in gular area
- Iodide required by fish for the synthesis of T3 and T4 (T3 active form)
- Iodine exists in 3 forms - Iodide (I-), dissolved organic iodine (DOI) and iodate (IO3-) latter is not available for absorption across the gils and GIT
- Low iodide or DOI in water or food, ozone disinfection, nitrates (competitively inhibit iodide uptake across gills), organophosphates, PCBs
- Signalment - more common in elasmos and tropical marine teleosts
- Findings
- Bony fish - slowly progressive opercular flaring common, often UNILATERAL, pink/yellow or tan soft tissue mass at base of gill arches
- Elasmos - slowly progressive soft swelling in the ventral midline just caudal to the mouth, may see dysphagia
- Ddx: neoplasia (carcinoma, adenoma, papilloma), infx/inflammatory lesions (thyroidities), hematoma, parasitic cysts (myxozoan pseudocysts, microsporidiann xenomas, larval nematodes)
- Dx
- c/s and response to tx MC
- Iodide and nitrate measured in water
- Iodide should be 0.03-0.06 mg/L in SW, nitrate <70
- US of thyroid in elasmos
- Plasma T4 may be low; T3 and TSH low in fish, assay may be unreliable
- Diffuse hyperplastic, diffuse colloid, or multinodular colloid on histo
- Husbandry
- Improvement in weeks-months with husbandry changes
- Add potassium iodide if low, reduce nitrate levels (water changes)
- Review ozone disinfection to see if dose needs to be lowered
- Medical tx
- Iodide suppl w/ K iodide PO weekly
- Others reported: levothyroxine, methimazole PO
- Prevention
- All elasmos should receive KI 1-30 mg/kg PO once weekly i.e. Mazuri Vita-Zu Shark/Ray tablets
- Regular water changes in closes systems to replenish micronutrients and remove nitrates, measure nitrates
- Measure iodide levels in systems with ozone disinfection
- Nutritional.
-
ZP - Iodine deficiency (goiter).
- Elevated nitrates, ozonation contribute.
- Nitrates inhibit I- uptake by the thyroid gland.
- Oxonation converts I- to IO3, biologically unavailable.
- Inputs may not be sufficient (still occurs in aquaria despite dietary supplementation and iodine additions to water).
- Thyroid is not a discrete organ in teleosts.
- Hyperplasia can result in grossly or microscopically evident hyperplastic thyroid tissue in various parenchymatous organs.
- Dx – CS, histo, ID low I- levels in water and feed.
- Total water iodine determination not sufficient, will not differentiate biologically available I- and IO3 forms.
- Serum thyroxine levels can be assessed (baseline and tx response).
-
ZP - Iodine deficiency (goiter).
15
Q
Discuss obesity in fish.
Where do they deposit fat? How does it differ between teleosts and elasmobranchs?
What are some potential causes?
What diagnostics can be done to confirm this disease?
What husbandry and medical treatments can be done?
A
- Obesity
- Bony fish deposit fat in their coelomic cavity, viscera and muscle; elasmos deposit fat in their liver
- r/o other causes of coelomic distention ie obesity
- Etiology
- Excess food intake, lack of fasting periods, inappropriate diets (ie diets high in pelagic fish to benthic crustaceans), diets high in PUFAs, high carb diets
- Lack of activity, enrichment
- Hormonal
- Lipomas, steatitis
- Hepatic lipidosis can be pathologic, can be challenging to differentiate from normal fat deposition in liver
- Signalment -all
- Findings
- Coelomic distention, incr muscling of epaxials
- Incr muscling in pelvic fins and over pelvis in skates/rays
- Bilateral exophthalmos
- Poor reproductive success
- Liver disease
- Ddx
- Other ddx for coelomic distention
- Hepatomegaly ddx: infectious hepatitis (mycobacteriosis, digenes, myxozoans), hepatic lipidosis, hepatic neoplasia, hepatotoxins, polycystic liver disease, cardiac disease, drug-induced hepatomegaly
- Dx
- Visual exam +/- Coelomic aspirate + US
- Comprehensive diet hx
- May not handle capture or chase well
- US - hepatomegaly
- Teleosts - liver has sharp edges, occupies <⅓ of coelom
- Elasmos - liver should not extend beyond pelvic girdle, or wrap dorsally around organs
- +/- Hypertriglyceridemia
- Gross necropsy - ceolomic fat; enlarged, pale, friable liver, high hepatosomatic index
- Histo - hepatocyte swelling with vacuoles of varying sizes (oil red O, Sudan IV stains)
- Husbandry
- Avoid sudden fasting, gradually restrict diet (i.e. 20% decrease repeated in two weeks)
- Introduce more varied diet items to mimic wild type diet
- Incr enrichment, foraging opps
- Medical tx
- Rarely indicated, nutritional support if inappetent
- Silymarin, SAMe, milk thistle may help
- Prevention
- Suitable diet, envt
