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Biologia > Clima - “ Estudo de Caso “

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Climate - “ Case Study “ : Garden fishpond water temperatures

Garden fishponds description and location
Meteorological information
Final results


Outdoors facilities are no doubt the most ethical, suitable, constructive and efficient method of captivity fish keeping.
Most common garden ponds are unquestionably bigger than any indoors tank and, off course, can contain larger water storage space by that reason. Besides space, a aforementioned excellent argument, there are also a few other excellent points of view to take in consideration, like the benefits of sun light, ecological conditions as well as... all we need, to recreate, at our own home, any natural habitat, better than in whichever other confinement setup.
For climate reasons, sometimes our local weather conditions are quite far from the original with reference to most species. For the most part of alien ( exotic ) fish species, standing outdoors for longer than certain precise periods of the year can represent a risk, either due to high temperatures during the hot peeks or, most commonly and frequently, by cold narcosis during winter colder months.
Unlike in the present days, by 1983 the pet fish market offering in Portugal was undoubtedly poor. The quality of imported fish, the amount of available species as well as the number of existing pet shops dedicated to fish as well as the service quality of most of them, ( regarding the fish trade ), were truly awful.
The World Wide Web was rather far from being a popular way of communication and knowledge, like nowadays. By the 1980’s, the experience and know how exchange among hobbyists was, in fact, a quite infrequent episode, ( particularly outside large urban areas ).
In rural areas, the number of hobbyists itself was frankly low, as small was the number of these who had one or even two tanks with exotic fish and could stand more than one year engaged with aquaria. Such unsuccessful panorama was justified by some unfortunate experiences due to lack of information, insufficient support provided by pet shops to costumers. This was the reality predominant in small localities.
Despite of that, there was a sort of fish keeping community, composed by hobbyists, sometimes meet up each other at pet shops or introduced to the “ tribe “ by other older members. The oral diffusion of know how was in fact an excellent source of knowledge and information, first and foremost for a beginner.
As expectable, under such verbal acquaintance tradition, rumours and some inaccuracies have gain a lot of significance inside the overall context, as time goes by; especially with reference to some species biology and technical stuff matter.
Among the most popular myths, some particularly intriguing ones at local aquaria folklore gossip about available “ tropical “ favourites who could in fact survive at winter cold outdoors, even if they were sold as fish who might not thrive outside of a heated tank or, by other words, who would never been kept below 21ºC.
Inspired by a restricted and very deprived offer, composed by merely 2 ( yes you’ve read well... two ) “ cold water “ fish species, I haven’t resist too long the call that encourage me to test some of those confidential “ urban myths “.

Optimistic by that hypothetically big pall’s secrets, that everybody knew it all ready amongst “ provincianos “ ( countryman ) hobbyists I start to plan my actions.
Fallowing this powerful impulse, I have decided to provide some biodiversity at my outdoor collection. Yes, undoubtedly it was indispensable to find something different from the two current alternatives, Carassius auratus and Cyprinus carpio fancy strains, ( definitely low category ones, but the single accessible at the Portuguese pet shops by that period ).
This was the start for an adventurous new world at one of the modest “ bogs “ ( well... a kind of artisanal fishponds ), hollow out at a remote area of the backyard ( without total and obvious assent of my father ).
Native species didn’t count for this propose, essentially by ecological scruples, ( in addition to the fact that, by those days, my aesthetic model about fish attractiveness had nothing to do with the faded tones awfully common in a largest part of our indigenous wild species ).
My first alternatives have been two invasive species – Gambusia holbrooki ( as a mark of my primordial passion regarding Poeciliids ) and Lepomis gibbosus ( by the pleasant appearance and magnetism and vibrant flush of this interesting sun fish, besides the fact that it could look like a lot a good cold resistant alternative for my beloved tropical Cichlids ).
The first innovation demarches with reference to the introduction of new species, classified at the sail market as the so called “ warm water fish “, have started in the summer of 1983.
A decisive condition was price, availability, as well as other hobbyists testify or similar experiences and low temperatures accidental exposure narratives.
Tanichthys albonubes and Danio rerio have been chosen to start the process for the reason that, the most part of the eyewitness tradition, did become public a number of excellent results on cold resistance with these two in particular.
Anyway, this becomes the most evident avant-garde selection, as alternative for those conventional two options related to the sail of the implausible glass globe aquarium choices.
After a few weeks of release it was very obvious and clear that predatory pressure was reducing to a residual number ( or even to total extermination ) the group of the two above mentioned “ tropical “ species, selected for the wintering outdoors experiment.
By the end of that summer, the first species to leave the pond was Lepomis gibbosus and, not long after, also Gambusia affinis as well as Cyprinus carpio, immediately next, all transferred to another location.
In September 1983 I have made a new reinforcement of the original group with new exemplars to replace the predated ones.
Following that winter, in spring 1984, to face the fact that corroborate one of the “ urban myths “ was a big surprise beyond any of my original belief. Both species had thrived well and could resist the lower temperatures outdoors.
My great concern after the first revelation was how to put in plain words such end result, especially while taking in consideration a “ tropical “ fish from India ( Danio rerio ).
This revelation brought in to my mind a first dilemma... how far, and for so long, lower temperatures could be reached in our open air fishponds ?
For a start, this uncertainty was not so important.
The biology and original wild geographical distribution, regarding a large number of the available tropical fish ( the easy to get at the Portuguese pet shops by than ), did result in a handicap for a correct evaluation of the most evident candidate species to spend the next winters out-of-doors. Even if there was the required data available, I hadn’t the slightest idea about the cold limits as well as how long deadly temperatures could be expected in standard meteorological conditions.
In addition, even the favourable conditions for genuine tropical species could be speculated, but never with accurate rigour evaluated in real basis.
Impelled by such curiosity, I start to take surface water temperatures readings weekly from this specific garden pond.
Soon it was quite clear that, for the aimed results, such procedure was frankly disappointing. At least daily collections should be done, in particular for an adequate method on the subject of a ( complete as possible ) image regarding the real thermal finger print of my “ bog “.
The lack of proper data and information did cause a few regretful disasters on the way to evaluate cold resistance and lower temperature limits for some of the tropical favourites. These remorseful mortalities and the need of a predictable and safe outdoors maintenance for exotic fish, pushed me towards the actual methodology, which have produced the below mentioned results.

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Fishpond #1 view.

Garden fishponds description and location :

Fishpond #1

The fishpond under observation between January 1985 and December 1995 had a rectangular shape, measuring 4 metres wide by 8 metres height.

The orientation was North/South on its larger axis.
With a 60 cm deep it had comprised something around 19 m3 ( 19.200 litres ) water capacity.
Construction technique was extremely simple and artisanal. A simple cavity of the precise size of it was excavated on the soil and covered with a polyvinylchloride ( PVC ) flexible film, ( up to 0,18 mm thick ).
This material was the best choice for the purpose in mind, thanks to its relatively low cost and predicted short extent for such experience.
Time was in fact a setback. The most evident inconvenience was the periodic need of the film replacement.
After exposure to sun light, in a relatively short time, physical properties experienced a quite fast degradation and mechanical properties showed trends of decrepitude in the course of photo-oxidation.
Located at South periphery, close trees top hurled some shadow over the fishpond, between the end of October and the beginning of March, reducing this way the water surface exposed to sun light to less than half by winter solstice.
There was no guard at all in opposition to wind action.

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Fishpond #1 view.

Fishpond #2 view, phase 1 - before 2000 ( winter ).

Pond #2

The fishpond under observation between January 1996 and December 2006 ( except for 1997 and 1998 ), was another fishpond chosen to proceed with the observations in course.
Such adjustment was forced by land use and the imperative call for of urgent deactivation of Pond #1.
This second one is still active and has also a rectangular shape, measuring 3 metres wide by 7 metres height.

The orientation is East/West on its larger axis.
With a 90 cm deep it comprises something around 19 m3 ( 18.900 litres ) water capacity.
Initial construction technique was, during phase 1, the same as Pond #1. With the introduction of new and improved offer in the market, the first film material old on this second fishpond was significantly better and quite further resistant to U.V. rays, ( as well as to photo-oxidation in general ). Such enhancement had allowed longer handling and less repairs of the water container layer.
After September 2000, a more effective setup took shape, with the selection of a new material, made specifically for fishponds - the 0.80 mm PVC pond liner or, to be more precise, a elastomer ( EPDM rubber - ethylene propylene diene monomer rubber ).
This material is still at use with no problem at all so far. It reveals to be ecologically safe and is prove to have a considerably longer durability than the preceding alternatives.
Prior to 1999, also located at South periphery, near by trees tops hurled some shadow over the fishpond. Between the end of November and the end of February, the water surface exposed to sun light was reduced to less than 30% at winter solstice. After the fall down of the trees, for a car parking construction at those grounds, Pond #2 lost all the shadow.
Opposition to wind action did never also exist.

For both fishponds the common location is in Vila Nova de Santo André, District of Setúbal, Santiago do Cacém ( town hall ) in South-western of Portugal, at a locator around the geographical coordinates of 38º03’ N e 08º46’ W ( common
graticule DM ).

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Fishpond #2 view, phase 2 - after September 2000.

Methodology :
All through the first stage ( from January 1985 to December 1996 ), temperature readings were made with mercury-in-glass thermometer ( aquaria type ).
To standardize results as well as to correct any inaccuracy, ( particularly between 0ºc and 40ºC ), both thermometers readings were compared with a digital electronic thermometer.
These tests were taken for certifying and calibrate the temperatures measured as good as possible.
In both cases, the mercury-in-glass thermometers remain floating all the time and removal from water meant for examination, took only a few seconds, just the time required for data interpretation ( temperature reading ).
Data collections happened usually between 8:00 and 9:00. On the odd occasion, some readings have been done between 18:00 and 19:00, depending on convenience or weather conditions. Nevertheless, an overwhelming preponderance of the readings had taken place at morning period. Only a few had taken place at the end of the day ( from 18:00 to 19:00 ).
From January 1999 to December 2006, the mercury-in-glass thermometer was replaced by a digital electronic one - Hanna Instruments HI 8424 ( pH, mV, ºC ).

Again the performance of this new equipment was compared with the same standard digital equipment used for similar operation with the preceding two mercury-in-glass thermometers on service before it.

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Meteorological information :
The next information have resulted from some research and was checked with a few scientific papers about “ Lagoa de Santo André “, a coastal lagoon of sandy soils originated by marine erosion or associated to old fluvial processes, located only 2.500 metres away in strait line.
According one of my sources - ( CEZH / RNLSAS 2004. Reserva Natural das Lagoas de Santo André e Sancha - uma contribuição para o plano de gestão. Instituto da Conservação da Natureza / Centro de Zonas Húmidas ) – local climate can be regarded with reference to the fallowing description :

« The climate on this area can be described, in general terms, as a Mediterranean with a strong maritime ( Atlantic ) influence – mild long summers, with low precipitation and gentle short winters. The most important rain period take place in December and January, ( Pinto, 1995 apud CEZH / RNLSAS 2004, page 25 ).
In the vicinity of the coastline, mist ( 1 and 2 Km visibility ) happens in 90 days/year ( average ) and fog ( visibility less than 1 Km ) during 28 days/year ( average ). Predominant winds are NW and the number of cloudiness sunny days/year is high, ( Pinto, 1995 apud CEZH / RNLSAS 2004, page 25 ).
According with the “ Plano de Bacia Hidrográfica ( PBH ) do Sado “ – ( Sado River Hydrographical Basin Plan ), mean pondered annual precipitation in the region is 621 mm.
The mean value of annual medium pondered temperature is 15,9ºC.
July and August are the warmest months, ( 22,6ºC ), while January the coldest ( 9,6ºC ).
The mean value of annual maximum pondered temperature is 21,9ºC with highest value in August, ( 30,5ºC ), with minimum in January ( 14,4ºC ).
The mean value of annual minimum pondered temperature is 9,8ºC with highest value in August, ( 14,8ºC ), with minimum in January ( 4,8ºC ).
Annual pondered insolation value for the Sado River Hydrographical basin is 2.745 hours/year. June registers 375 hours of sun and December 142 hours, ( PBH do Sado 1999 apud CEZH / RNLSAS 2004, page 26 ).
On this region the insolation is high, ( around 57% of maximum for the latitude ), with 2.976 hours/year in Santiago do Cacém ( town hall ).
Predominant winds are NW for the entire region, no matter how far from sea shore. Mean wind speed varies between 13 Km/hour in September and 19 Km/hour in May. Annual mean is 16,7 Km/hour.
Annual mean reference evapotranspiration for the Sado River hidrographycal basin is 1.144 mm, with July accumulating the highest values ( 183 mm ) and December the lowest ( 29 mm ), ( PBH do Sado 1999 apud CEZH / RNLSAS 2004, page 26 ) ».

Next we will have a few climate information from one of the meteorological stations inside the area of the RNLSAS – Reserva Natural das Lagoas de Santo André e Sancha ( Santo André and Sancha Lagoons Natural Reserve ), at the above mentioned source - ( CEZH / RNLSAS 2004. Reserva Natural das Lagoas de Santo André e Sancha, uma contribuição para o plano de gestão. Instituto da Conservação da Natureza / Centro de Zonas Húmidas ).
The original source of the data below presented is the Instituto de Meteorologia de Lisboa, Novembro de 1995. Segundo Alcoforado et al., 1993, ( Farinha & Silva 1997 apud CEZH / RNLSAS 2004, page 26 ).

Estação Meteorológica de Monte Velho ( Monte Velho Meteorological Station )
Location - 38º04’N 08º48’W
Altitude - 17 metres
Period - 1973-1986 and 1971-1990

Mean annual temperature
Minimum - 10,0ºC
Maximum - 20,3ºC

Mean temperature on the warmest month
Minimum - 13,8ºC
Maximum - 25,1ºC

Mean temperature on the coldest month
Minimum - 5,9ºC
Maximum - 15,8ºC

Precipitation annual mean - 523,4 mm
Emberger index - 94,5 mm

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Final results :
Far from consider this as scientific valuable or even significant work for climate knowledge, such permanent data collection can help us to evaluate local conditions for fish keeping in garden ponds outdoors.
Besides the information revealed annually throughout the links below, the readings collected during the past years can, unquestionably, help one to get an remarkable idea, not very far from reality.
Next we have first a few graphics with some conclusions and below the collected data year by year.


Figure 1 – This graphic represents the twelve-monthly thermal evolution resulting from the temperature sequential readings along the period of this experience, when the two fishponds were under observation.
Between the bold lines, in the highlighted area with a chromatic gradation between blue ( for cold ) and red ( for warm ), we can visualize the standard high and low limits, expected for each point in time all along the year.
The borders represented by the thin upper and lower lines, are the extreme temperatures. These are superior and inferior absolute registered values, which happen no more than sporadically, going far above or below the expectable limits. Such edge conditions are more frequent only under extraordinary or irregular weather conditions, like during meteorological unusual events.

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Figure 2 – While considering a relatively small water body like a garden pond, we should ever keep in mind that thermal behaviour is relatively compared with a natural small poodle or restricted bog. All natural or artificial low deep small pieces of water, ( particularly if we are not talking about running water ), do present a remarkable tendency to fluctuate very closely in conjunction with air temperature. Any sudden variation in air, do comprise some, more or less instant, effect on those little shallow water bodies.
If we assess the results of both fishponds temperatures and compare them with neighbouring natural running water bodies, like Santo André lagoon tributaries ( grey area ), some discrepancy becomes quite obvious.
It’s particularly clear than in some periods lower pond temperatures are in fact colder than in natural neighbouring stream habitats, while in other moments the upper limits are actually superior.

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Figure 3 – This is a similar compositions on the previous graphic ( figure 2 ).
The only difference is that when the two experiential garden ponds have presented lower minimum temperatures ( blue ) or higher maximum temperatures ( red ) than in natural neighbouring larger habitats, these periods are highlighted and limited in time.

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Figure 4 – This graphic correspond to lower and upper annual temperature limits, along the experience period, year by year.
Absolute minimum ( 5,5 ºC ) was recorded in January, 24th 1992 ( 8:04 ) and absolute maximum ( 34ºC ) was recorded in July 18en 1991 ( 18:27 ).

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Figure 5 – Mean annual temperature, all along the experience have oscillated between 17ºC in 1993 and 18,8ºC in 1989. Average annual temperature was 18ºC.

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Figure 6 – This graphic intend to show the potential of each year for keeping no native species outdoors.
For an understandable motivation, our best attention was oriented toward exotic ( primarily tropical ) temperature conditions.
Red bars represent best odds for tropical’s outdoors. Above 20ºC any “ warm water “ species is safe, so here we can spot how many days each year temperature was above that edge.
Any time the red bar was above the yellow area ( above 100 days ), it was a most advantageous year, especially taking in consideration the local climate. Remember that longer period in open air produces enhanced circumstances for a group evolution. On a fishpond, demographic outcome is evidently improved; general health and growth are maximized and a long permanence under such trustworthy conditions ( quite close to natural ones ), can only benefit any collection ( population or strain ) held in captivity.
On the opposite level, the blue bars, help us to estimate and oversee the critical lower limits for temperate regions species. Off course we are talking about those not very well naturally prepared to resist our cold, but quite well capable of support and to survive over some clement or less “ frosty “ winters.
Above the yellow area, ( more than 25 days below 10ºC ), those years are potentially lethal for many of the temperate region originated favourites.
Although it doesn’t work precisely like that, as extensive as the low temperatures period goes, more side effects and negative consequences from cold exposition can be severely noticed, compromising fish survival and recovering or fitness.
Anyhow, even when talking about native species, exotic acclimated or introduced ones, there is an unmistakable rule to get from this piece of information... as largest the difference between the red and blue bars, as more favourable the year in question can be understood in terms of temperatures.

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