description and location
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
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
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
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
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
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
In addition, even the favourable conditions for genuine tropical species
could be speculated, but never with accurate rigour evaluated in real
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.
Back to top
Fishpond #2 view, phase 1 - before 2000 ( winter
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 )
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
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 ).
Back to top
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
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
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.
Back to top
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
« 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
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
Back to top
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 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
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
Back to top