To feed, or not to feed. That is the question. (along with how much, how often and when)

The seemingly simple act of feeding one’s pond fish, whether they be  Koi, Goldfish, Orfe or other variety, can quickly become confusing when one is bombarded with admonitions such as- “You are feeding too much!”, “You are feeding too little!”, “Too often!”, “Not often enough!”, “Wrong time of day” ad nauseum et confusium.

Perhaps if we were to take the time to examine a few basic facts surrounding the digestive processes and natural feeding behavior and food preferences of fish, the solution may reveal itself.

The focus here will be placed on Koi/Carp (Cyprinus carpio) given that this is presently the most popular of pond fish.

When examining the digestive system of a Koi/Carp, we are immediately presented with a glaring physiological difference between Koi/Carp and most other fish. Koi/Carp do not have stomachs! They instead have just one continuous gut. In a natural environment, food seems to be ingested in small particles in a relatively steady stream instead of intermittently in large units, so the storage function of a stomach probably is not missed.  Digestion takes place in this intestine, which is twice the length of its body. Different enzymes are secreted by the pancreas along the intestine. The system works best if it is able to process a steady supply of food. This is why Koi/Carp are constantly rooting around for something to eat. At the back of the mouth are the pharyngeal teeth. These are aligned in three rows on each side of the mouth, with three teeth in the innermost row and one tooth each in the two outer rows. The teeth are positioned below a tough calcified pad. Food is ground between it and the pharyngeal teeth before being passed to the first part of the gut called the esophagus.

Koi/Carp cannot digest all foods efficiently. They might eat bread and sweet corn, but it is difficult for them to digest them. Fibre, especially grass and alfalfa meal, is important as it allows the intestine to grip the food and keep it moving. Worms, insect larvae and fresh vegetable matter are only partly digested and serve as roughage to keep the intestine active and healthy. Koi/Carp will also ingest silt and other indigestible detritus to bulk out their diet.

Koi/Carp is an agastric fish, meaning absorption of nutrients is highly dependent on the rate of feed passage in the gut. Variables which influence gastric evacuation time, along with feeding rate, include temperature, season, activity, body size, gut capacity, satiety, and metabolic rate. The gut transit time (length of time the food takes to pass through the gut), just based on temperature, varies greatly from 16 hours at 25ºC/77F to 60 hours at 12ºC/54F.

Koi/Carp is also an omnivorous fish that possesses excellent sight, extremely excellent hearing, highly developed taste and, according to some, a sensing mechanism akin to what bats use so effectively. They also possess an excellent memory. Once they have a negative experience with a food item, they will avoid it at all future times.

Research has shown that, even though they are continuously grazing and rooting around for tidbits and tasty morsels, Koi/Carp possess a natural feeding rhythm. The research was conducted under temperatures ranging from 4C/39F to 34C/93F using both juvenile (61g – 91g) and adult (630g – 850g) fish. There were two periods that main feeding activity occurred: 8:00 – 11:00 a.m. and 19:00 – 23:00 p.m. with adults consuming 27% and juveniles consuming 66% of their total daily intake in the two combined time periods. This would seem to indicate that while a certain time period feeding preference is evident in young Koi/Carp, this preference wanes with age.

More importantly this study showed the effects of temperature on feeding behavior. Both adult and juvenile Koi/Carp reached the maximum daily feeding rate at 28°C/82F, being 2.84% and 12.06% of body weight, respectively. At 14C/57F, the daily feeding rate of adult and juvenile reached 1.21% and 2.63% of body weight, respectively. At 6°C/43F, though both adult and juvenile would still feed, the feeding quantities were only 0.01% and 0.35% of body weight.  The daily feeding rate of adult and juvenile reduced suddenly after reaching 34°C/93F and the daily feeding rate was only 0.74% and 9.45% of body mass, respectively.

Separate research was conducted to determine the effects of feeding frequency on final weight, daily weight gain and feed efficiency. Adult Koi/Carp were fed over a period of 82 days using three (3) feeding strategies – 1) hand feeding twice a day to apparent satiation, 2) continuously by means of an automatic feeder over 2 x 6 hour periods and 3)   continuously feeding a fixed rate of 1.4%  body weight using an automatic feeder.

Strategies 2 and 3 improved protein digestibility, whereas only feeding strategy 3 increased organic matter digestibility.

Have we arrived at an answer to the original Title question – To feed or not to feed?

Yes, but not entirely.  We know that we must take certain factors into consideration.

        1. Age of fish – Young fish need to consume a higher percentage of their body weight daily in order to sustain healthy growth. As the fish age, growth becomes less of a factor and the feed demand is reduced.

        2. Temperature – The metabolic demand greatly diminishes as temperatures are reduced. Digestion rate is also drastically reduced as evidenced by longer gut transit time.

The chart below lists suggested daily feeding levels (% of body weight) based on temperature and body weight.

Fish weight(g)  Temperature ©	>5	5 - 20	20 -50	50       -       100	100     -       300	300      -       1000
<17	6	5	4	3	2	1.5
17 - 20	7	6	5	4	3	2
20 - 23	9	7	6	5	4	3
23 - 26	12	10	8	6	5	4
>26	19	12	11	8	6	5

(This link is great for determining a close guesstimate of fish weight.        http://www.cnykoi.com/calculators/calclenw.asp)

        3. Frequency – It has been shown in laboratory tests that continuous feeding is most beneficial and more closely coincides with natural feeding patterns. Unless one is willing to purchase a programmable automatic feed dispenser, the continuous feeding option is an impossibility, but the greater the number of feeding periods that one can manage the more the fish will benefit.

Beyond the three aforementioned factors, the answer becomes decidedly muddled. One must also take into consideration:

Type of pond – Classic Koi or Ecosystem or some hybrid style. The more closely that a pond emulates a true ecosystem, the greater the abundance and availability of natural food sources such as phytoplankton, zooplankton and benthic organisms and consequently the lesser need for supplemental feeding.

Stocking levels/Fish load – Here the problem is not overfeeding the fish, but overfeeding the entire system. Unless an exceptional capacity for bioconversion is available, an overstocked pond cannot accommodate the additional organic matter generated by adequate feeding levels. In addition, soon after feeding, the fish experiences an increased Oxygen demand quickly followed by an increased excretion of Ammonia. Neither of these natural occurrences bode well for an overstocked pond.

Every pond is unique, so fish feeding practices must be custom tailored to each pond. There is no  ‘One size fits all” approach to proper feeding, but following the above guidelines, if you are willing to expend a little extra time and effort, can get you pretty darn close to what is best for the fish and the pond.

pH - Update

A study [ Long-term effects of water pH changes on hematological parameters in the common carp (Cyprinus carpio L.), Mahdi Ghanbari1* and Mansoureh Jami2] was conducted  for the purpose described in the study abstract below.

 “The aim of this study was to examine the effects of water pH changes on certain hematological parameters of fingerlings of common carp (Cyprinus carpio), in water with different pH (acidic and alkaline). Fingerlings of common carp were subjected to acidic (pH 5.5 and 6.5) and alkaline (pH 8.0, 8.5 and 9.0) water for 21 days. Control groups were maintained at neutral pH. The result showed that exposure to both acidic and alkaline water exerted stress on fish and considerably affected the hematology of fingerlings of common carp. Cytological study revealed that such swollen erythrocytes with centrally located swollen nucleus and also immature erythrocytes were observed in fingerlings exposed to pH 8.5 - 9.0. Exposure to the two extreme pHs (pH 5.5 and 9.0) caused significant reductions (P < 0.05) in total erythrocyte count (TEC) in common carp. A significant reduction (P < 0.05) in the hemoglobin content was observed at the two extreme pHs 5.5 and 9.0. The total leukocyte count (TLC) was reduced at pH 5.5, but only after a brief increase at pH 6.5. Alkaline range also experienced a reduction in TLCs at pH 8.0 and underwent further reduction with increased pH. Blood glucose was significantly higher (P < 0.05) in fingerlings exposed to both acidic and alkaline waters and the increase was proportional to the degree of pH change. Serum protein levels were also significantly reduced (P < 0.05) following exposure of the fingerlings to both acidic and alkaline conditions. The changes in hematological parameters of the fingerlings of common carp indicated that the change in water pH might have caused the ion regulatory and acid–base disturbances originating at the gill leading to the altered internal pH, electrolyte and osmotic balances that imply an increase in energy consumption to restore homeostasis instead of other physiological functions, weight gain and growth.”

This study further substantiated previous widely held beliefs concerning the effects of extreme values of pH (5.5 and 8.5 – 9.0) on Cyprinus carpio (Koi) by defining the physiological changes that occur within the blood chemistry at acidic and alkaline extremes in pH values. Red and white blood cell levels and production were noticeably negatively affected; hemoglobin levels were also severely affected, as were glucose and serum protein levels. The possibility of respiratory stress was indicated by the reduction of hemoglobin in both acidic and alkaline conditions.

Although the pH range of 6.5 – 8.5 remains widely accepted for homeostasis, this study also indicates that certain levels of stress are experienced as the limits of this range are approached and chronic exposures to these range limits could result in extended physiological impairments.

This is not to say that brief exposures to these pH extremes are harmful. They are experienced by all fish in the diel rhythms that occur in aquatic eco-systems. When these levels become problematic is when the average maintained pH level is near these extremes.

Temperature---Revisited

In two (2) recent studies, determinations were sought as to the effects of temperature on (1) egg development and spawn growth in Koi/Carp (Cyprinus Carpio) and (2) foraging and growth rate of juvenile Koi/Carp (Cyrpinus carpio).

It was shown in the first study that “The present results suggest that water pH 7.5 at water temperature 26°C/79F is best for hatchability of eggs and pH 7.39 for growth of spawn of Cyprinus carpio at same water temperature.

  (Optimal water temperature and pH for development of eggs and growth of spawn of common carp (Cyprinus carpio)

P.H. Sapkalea*, R.K. Singha & A.S. Desaia)

The second study showed “Temperature had a significant and positive effect on the foraging and growth of juvenile common carp Cyprinus carpio (90–105 mm) between 16C/61F and 28C/82F …… These outputs suggest an increase in foraging and growth of C. carpio according to a thermal gradient that were maximal between 24C/75F and 28C/82F.

   (Effects of temperature on the foraging and growth rate of juvenile common carp, Cyprinus carpio   D.O. Oyugi1, J. Cucherousset2, D.J. Baker, J.R. Britton )

Comparing the results of these two (2) studies we quickly see that the temperature of 26C/79F was independently arrived at as the optimal temperature. This temperature is very close, though slightly lower, to what we stated in our previous blog post on temperature in December of 2010.

“Even though no discomfort (stress) is manifested between 20C/68F and 34C/93F, ideally we want the temperature to be close to the midpoint of this range which is 27.5C/81-82F.  This is well above the median temperature recommended by many sources, but is shown to be the ideal temperature for the Carp’s (Koi’s) optimum metabolism.”

Are Pond Ionizers Safe? You be the judge.

Certain manufacturers of Pond equipment decided to borrow a technology from the Swimming Pool industry and, with maybe some minor tweaks, promote it as an exciting breakthrough in controlling Pond algae. Presenting the IONIZER!

Through the controlled release of Copper, Zinc and Silver ions into the pond’s water column, algae growth can be controlled and in many cases eliminated. This, on the surface, is great news for Pondkeepers. No longer is it necessary to use expensive and hard-to-correctly-measure chemicals. Just set the Ionizer to the desired level and algae disappears.

Sounds great! However, there is more to be considered than just what the advertisements claim. What are the other potential and likely results from use of this device that the manufacturers are not telling us?

Let’s look at some of the manufacturers’ claims as regards Ionizers.

Company #1 - “Destroys Bacteria                                 

                              Kills Algae

                              Reduces chemical cost

                              Eliminates chemical odors

                              Reduces maintenance

                              Environmentally Friendly

                              Costs pennies per month

                              Helps reduce filtration

                              Fish safe

                              Includes 2" T Fitting”

Company #2 -     “Safe for fish and plants

                            Low maintenance

                            Clears water without the use of harsh chemicals

                            Easily installed in any new or existing water feature

                            Treats ponds up to 25,000 gallons

                            Level of mineralization is controlled by the LED panel

                            Cast mineral anodes are self-cleaning

                            1 year warranty”

Company #3 –“Drastically reduces pond maintenance

                              Crystal clear water without the use of chemicals

                              Eliminates unsightly water conditions

                              Simple to install

                              Safe for fish and plants

                              Not toxic to animals that may drink from the pond

                              Energy efficient (less than $ 1 a month in electricity cost)

                              Treats ponds up to 25,000 gallons”

Understandably, the first concern of a Pondkeeper is whether a product or treatment is safe for fish. All three (3) of these manufacturers declare that the (proper) use of this device is safe for fish. Let’s take a closer look at this claim.

All Three (3) manufacturers include test strips for monitoring Copper levels with Two (2) of the manufacturers recommending maximum Copper levels at 0.25 mg/L and the remaining manufacturer recommending 0.30 mg/L as the maximum level of Copper.

Copper is a heavy metal and in low concentrations can be toxic. In addition, like other heavy metals, such as Mercury, it is a bio-accumulate. This means that once it is ingested by an organism it remains in that organism for an extended period of time, in many cases, for life. Any additional ingestion only increases the level that is already present in the organism until eventually a certain level of toxicity is reached. For terrestrial organisms, this level is determined primarily by the ingestion of food and water, but for aquatic organisms, if the Copper is in suspension as ions, it may be ingested during the respiration process also, as is the case with fis juvenile amphibians, certain insect larvae, true aquatic invertebrates and bacteria as well as the target taxa of algae. In the case of fish, it causes increased mucous production on the skin and the gills where it eventually interferes with the respiration process by blocking the absorption of Oxygen.

In assessing the potential toxicity of any substance to any organism, two (2) distinct levels must be determined, acute (immediate short term) and chronic (long term). Heavy metals have long been known to play an important beneficial and cricial role in animal and plant physiology, but at levels so low that they are undetectable by standard testing.

Considerably greater attention has been given, in recent years, to the effect of Heavy Metals and other chemical compounds on the environment. Research is ongoing in both the public and private sector. This research has resulted in some universally accepted toxicity levels as regards Heavy Metals.

The focus here will be on Copper. Copper, after Mercury, is the most toxic of the Heavy Metals. Copper’s toxicity is greatly influenced by water Hardness and pH. As water Hardness and ph increase, the toxicity of Copper is reduced. Here is an example of a couple of simple formulae that are used to define the accepted level of Copper in fresh water.

    Maximum Copper levels (in micrograms) at any time—0.094(hardness)+2 (where water Hardness is reported as mg/L  CaCO3.

     30 day average Copper levels (in micrograms)—0.04 average hardness (where water Hardness is reported as mg/L  CaCO3.

       (Environmental Protection Division, Ministry of Environment, Government of British Columbia)

Note - There are other formulas used by different government entities worldwide, but the final accepted levels of Copper vary by only a few micrograms.

Using these two (2) formulae, in water with a Hardness of 120 ppm for example, we find the recommended Copper levels to be 13 micrograms/L at any one time and the 30 day average should not exceed 5 micrograms/L  Knowing that one milligram equals 1000 micrograms, these results expressed in mg/L would be 0.013 mg/L and 0.05 mg/L. These results appear to be on the conservative side, but considering the fact that some aquatic organisms have a very low tolerance to Copper, these formulae are quite appropriate.

These are the Metal Safe Limit levels as defined in the Textbook of Fish Health: Copper 0.014mg/l More toxic in soft water; Zinc exacerbates toxicity; Combined both are dangerous; Zinc 0.01mg/l Synergistic with copper; 0.15mg/l In hard Water; Cadmium 0.03mg/l; Chromium 0.10mg/l; Lead 0.01mg/l In soft Water; 4.00mg/l In hard Water; Silver 0.03mg/l (mg/l is the same as ppm).

The author was unable to find any scientifically set copper toxicity levels for Koi, but several anecdotal sources were found that stated that Koi begin to show copper toxicity at 0.03 ppm along with the copper toxicity level for Koi at 0.3 ppm., which is at or extremely close to the Maximum levels suggested by the manufacturers of these devices. It should be stressed that no scientific studies were found that substantiated these levels. In fact, one study reported that Koi fry were unaffected by Copper levels of 1.00 mg/L.

It is important, however, to know the signs and symptoms of Copper toxicity in Koi. One of the earliest effects of  too much copper is apparent fish hypoxia, the loss of ability to use oxygen. Common symptoms of initial acute toxicity are fish gasping, disoriented (ataxic) at the surface, due to copper's hemolytic (blood cell splitting) and mucus-producing effects. Copper is a proteinaceous precipitant; that is, it causes your fish to produce more mucus. This may aid the in the suffocation or sloughing off of parasites, but also interferes with respiration through their skin and gills.

Of greater concern is the previously mentioned fact that all heavy metals are bio-accumulates. This accumulation leads to immunosuppression.  Fish are often observed suffering from bacterial infections for no apparent reason.   Water quality is optimum but low levels of copper and/or zinc are present. Metals are most toxic in low alkalinity and pH. This allows for a higher concentration of metal to remain dissolved. The accumulation over time immunosuppresses the fish and allows the normal pathogenic bacteria to gain the upper hand leading to ulceration and possible septicemia (bacteria in the bloodstream).

In eco-system ponds, along with the fish, the toxicity of copper to all other aquatic organisms is of equal importance. Considerably more data is available on the effects of copper on fresh water fauna due to the fact that they are present in every natural waterway and their numbers and diversity are prime indicators of the health of any aquatic eco-system.

Copper is extremely toxic to most invertebrates and the juvenile forms of most amphibians.

“Northern leopard frogs (Rana pipiens) were exposed to environmentally relevant concentrations of copper in water (control and 5, 25, and 100 microg/L, as CuSO4) in a static renewal system for 154 d from posthatch stage to metamorphosis. Tadpole survival, swimming performance, percent metamorphosis, time to metamorphosis, and survival during and time required for tail resorption were negatively affected in the 100-microg/L treatment.”

      -Adverse effects of chronic copper exposure in larval northern leopard frogs (Rana pipiens).

Chen TH, Gross JA, Karasov WH.

Available toxicity data on amphibians indicate copper 96 h LC50 values calculated in tadpoles ranged from 0.04 to 5.38 mg/L. Studies of other aquatic organisms show 96 h LC50 values ranging from 0.06 to 6.68 mg/L.

Representative toxicity levels for some other fresh water organisms are-

    Most snails – 8 - 41 micrograms/L; Cladocerans (including Daphnia) 5 - 213 micrograms/L; Amphipods 8 - 87 micrograms/L

Although the Mayfly is fairly sensitive to Copper, the majority of insects that have aquatic larval stages are tolerant, most notable Damselflies and Dragonflies, which are always expected visitors to any aquatic venue. These Odonates have the ability to store heavy metals in their exoskeletons where it remains harmless.

The inhibition, reduction or elimination of any member group of the aquatic food chain will have negative effects on the overall health of the eco-system to a lesser or greater degree depending on which species are residents of that particular eco-system and their relative position in the food web.. Nevertheless, any negative effect on an aquatic eco-system’s food chain and/or diversity will have deleterious effects on the entire system.

The only organisms that have not been discussed are the bacteria, in particular, the nitrifying bacteria. The results of studies on the toxic effects of Copper are quite surprising. Copper and Zinc appear to be the least toxic of the metals tested. Copper, at low levels, actually stimulates activity in  Nitrobacter. At levels up to 0 50 mg/L the Copper ion has no toxic effect on Nitrobacter. Instead, the stimulatory effect is readily apparent......Apparently. at 0 50 mg/L Copper has not reached the cross-over point where a chemical shows neither stimulatory nor inhibitory effects. This, unfortunately, is not true of Nitrosomonas. Growth of Nitrosomonas is greatly inhibited (about 60%) by Copper concentrations of 0.20 ppm. 

      Growth of Nitrosomonas europaea in batch and continuous culture  (Skinner & Walker 1960)
Copper was also found to be one of the most toxic metals to heterotrophic bacteria in aquatic environments.
Sadly, company #1 is partially correct in claiming that their ionizer “destroys bacteria”.

In conclusion, based on the above data, we arrive at these facts-

  -Ionizers can indeed control and, in some instances, eliminate many species of algae.

  -Within the manufacturers’ suggested range of use, 0 – 25/30 mg/L, neither Koi or Goldfish should exhibit any immediate effects of Copper toxicity. It has been shown that Koi fry can tolerate levels of 1.00 mg/L. Due to lack of any meaningful research, long term (chronic) effects are unknown.

  -Copper at low levels is extremely toxic to aquatic stages of most amphibians.

  -Most microorganisms exhibit toxic effects of Copper at extremely low levels and, where mortality does not occur, the effects are compounded in second generations.

  -The effects of relatively low (.20 ppm) Copper levels on one of the main species involved in Nitrogen conversion has the potential to cause major problems in the form of Ammonia spikes.

Considering the whole picture regarding the impact that an Ionizer may have on an aquatic eco-system, this author has no intention of availing himself of its use. There are other effective and absolutely safe ways of controlling and/or eliminating algae. You, the reader, may feel differently. After all, it’s your Pond and your fish.

You be the judge!

_______________

Update Nov. 29, 2012

There has long been a dearth of information regarding the toxicity level of Copper in Koi (Cyprinus carpio). Finally some figures are being established by scientific research.

According to a recent research paper (Dietary tryptophan changes serum stress markers, enzyme activity, and ions concentration of wild common carp Cyprinus carpio exposed to ambient copper

Fish Physiology and Biochemistry (2012) 38: 1419-1426 , October 01, 2012

By  Hoseini, Seyyed Morteza; Hosseini, Seyed Abbas; Soudagar, Mohammad), Carp exposed to 10 mg/L Copper exhibited mortality rates of 21.7 ± 7.6 % at 120 hours and 61.7 ± 10.4 % at 168 hours. Although this level of Copper is 40 times the (claimed) maximum levels generated by ionizers, I feel that it is safe to infer, because Cu is a bio-accumulate, that depending on the usage (level settings and duration of these settings) of ionizers, that Koi/Carp would exhibit physiological and behavioral signs of toxicity much quicker than was originally thought….months instead of years. Hopefully more definitive figures will be forthcoming.

______________

Update July 8, 2014

In this recent research paper - Acute effect of copper exposure on serum biochemical characteristics of common carp (Cyprinus carpio L.), Melika Ghelichpour the effects of low level exposure to Copper were markedly detectable.
"Effects of ambient copper was investigated on serum stress markers, sodium and enzyme levels in Common carp (Cyprinus carpio L.) over a 14-d exposure period. Fish were exposed to 0, 25 and 100 microg L-1 copper (as copper sulfate) and blood was sampled at 0, 3, 7 and 14 d after exposure. Serum profile was significantly affected by copper concentration, sampling time and their interaction. Increase in serum levels of cortisol, glucose, alanine aminotransferase and aspartate aminotransferase and decrease in serum sodium levels were observed in both copper-exposed groups, 3 d after copper exposure, which lasted until the end of the experiment. It is concluded that copper exposure causes stress response and sodium loss in common carp. Likewise alanine aminotransferase and aspartate aminotransferase increase after exposure which might be as results of either tissue damage or stress."
Note: Copper Sulfate readily disassociates in water producing Copper ions. The physiological effects would be the same with an ionizer.




_________________

UPDATE  June 23, 2015

Just released article

“ Health status of two ornamental fishes Poecilia reticulatae (Guppy) and Carassius auratus auratus (Gold fish) following exposure to therapeutic levels of Copper sulphate

M.H.B.W.M.D.N.H. Wickramasinghe* and A. Pathiratne”

…indicates that gill damage occurs in Goldfish at Copper levels of 0.10 mg/L and may not be completely reversible at levels of 0.30 mg/L and recommends that “precautions should be taken especially with the high concentration of CuSO4 (Copper) as it may lead to transient ill health conditions in the exposed fishes.”