Summer droughts and warmer winters are the new norm

Hortobágy Fish Farm (Hortobágy Halgazdaság Zrt) has a history of more than 100 years and is the largest lowland diversion pond system of Hungary owned entirely by the Hungarian state. Regular monitoring of the water in the ponds, chemical and biological analysis of water samples, stock transfers to wintering ponds, and the use of defences against predatory birds are some of the measures the company uses to mitigate the impacts of climate change.

Six independent but centrally managed pond units are used to farm carps at Hortobágy Fish Farm. e 3,000 hectares of pond surface are in a strictly protected Natura 2000 area of Hortobágy National Park. Ponds replaced the swamps drained during the regulation of the Tisza River 150 years ago.

e soil underlying the ponds is saline and so unsuitable for crop production. Water from the Tisza River is channelled to ponds where carp for the table is produced in polyculture with other species within three-summer periods. e company works with three strains of carp, Hortobágy mirror, Hortobágy scaly, and Hortobágy wild, developed by themselves on site.

Vertical integration of production

A full production system basically means that the company produces everything from roe to table-size sh entirely on its own. It maintains its own broodstock and has developed its own breeding protocols as well. Chemicalfree manure from organic farming is used for the production, which is based on algae and plankton. e sh is fed on cereals together with vegetable protein in addition to the naturally occurring feed in the pond. Seventy percent of the production is common carp, while the remainder includes silver and bighead carps, grass carp, European cat sh, perch, a small volume of pike and wild sh (e.g., crucian carp), which ensures the entire nutrient base of the ponds is utilised. Each age group raised in polyculture is removed from the ponds at the end of the summer and, to increase living space, is usually stocked in smaller populations into other, larger (50-100 ha) ponds. e primary target is to sell table-sized sh (2-3 kg), but the surplus from younger age groups is also marketed.

Market-size sh are sold both live and processed at a primary level mainly to Hungarian consumers through large supermarket chains—Auchan, Metro, Spar—or they are exported live to Romania. For these reasons, the company needs to harvest all year round. For the sake of pro tability, ponds shed during the breeding season are used again within the production period, i.e., after re lling with water the ponds are restocked usually from large ponds where for better growth the density needs to be reduced.

Harvesting starts typically in the fall. The water is released from a pond and the fish are gathered in a corner using nets.

Despite being a huge menace cormorants are virtually untouchable

The ponds’ location in a Natura 2000 area means the company must comply with specific rules and regulations regarding the environment including the local flora and fauna. However, the damage caused by fish-eating birds, mainly the great cormorant ( Phalacrocorax carbo ) and the pygmy cormorant ( Microcarbo pygmeus ), has significant effects on fish production.

The Hortobágy National Park Administration permits great cormorants to be scared off and their numbers reduced based on a specific quota. On the other hand, the pygmy cormorant is strictly protected, so scaring it off or culling it is prohibited. Based on experience, the daily volume of fish consumed by a large cormorant is 0.8-1.5 kg, and by a pygmy cormorant is 0.05-0.1 kg.

Single-phase fry rearing technology, where sh fry are transferred to ponds directly from the hatchery, is used on the farm. is requires a continuous increase in living space for the larvae, which are rst stocked in water a few centimetres deep. e slow ooding of a pond requires several weeks. Periods of summer droughts and the lack of water jeopardise the production of one-summer-old fry if the operating water level is not achieved in time and, additionally, the damage caused by pygmy cormorants also multiplies.

Growth rates depend on a number of factors

Production starts after the harvesting of table sh which starts in October. is is referred to as the fall harvest. Cleaning, disinfection, and re lling follows leading to the production/growing period. Two- or one-summer-old sh, or fry are moved into these ponds in the winter. In the past the possibility of damage caused by birds is reduced to a minimum by hard frosts that usually start at the end of November, when the ponds freeze. e ice cover ensures a peaceful wintering for carp at 4 °C. e farm manager uses the water temperature and the knowledge that carp starts feeding at a water temperature of 8 degrees C, but its metabolism only becomes active at 12 degrees C, along with other relevant information to estimate the growth rate.

e 5 t/ha manure introduced as basic fertilizer once the ponds have been disinfected and re lled over the autumn and winter ensures a peak in plankton levels in spring. Additional fertiliser introduced during the year based on the needs of the ponds ensures a high plankton level at the end of the summer. Supplementary feeds, corn, wheat, barley, triticale, or rye, help to optimise the growth rate of carp. When the plankton or benthic organisms produced in the pond decline, a supplement of plant protein is required, like sun ower seeds or lupins. is establishes an appropriate ratio of protein and starch which contributes to maintaining the sensory properties of the carp esh.

Warmer springs have prolonged the growing season

e e ects of climate change started to impact production operations 15 years ago though at the time only minor adjustments had to be made to the production technology. Today one of the greatest challenges is caused by changes in the seasons, i.e., a mild winter is followed by a spring with summer temperatures, resulting in a clear increase of the growing season. e primary problem is mild winters because of the lack of severe winter frosts and ice cover. Frozen lakes and rivers of the north magnify the invasion of great cormorants and pygmy cormorants, resulting in the migration of hundreds or even thousands of individuals. Waters in Hungary do not freeze, so the birds do not move on, but spend the winter in the country and are a serious threat to pond farms and to sh natural waters. It is almost impossible to keep them away with shooting, as they are even able to prey at night if it is clear. With this experience, in the fall the entire stock—groups of one-, two- and three-summer old sh—must be harvested and moved to wintering ponds from

November to April with a continuous water ow. e damage caused by cormorants is not limited to losses due to predation, but also results from the sh being constantly disturbed by the birds in the winter period if the sh are not moved to wintering ponds. As a result, their reserves are quickly exhausted leading to health problems in spring among depleted individuals.

Climate change tends to increase the cost of production

e cost of harvesting and wintering increases, among other things, due to multiple handlings of sh. Forage feeding of wintering stocks also means additional costs. To protect wintering ponds, “threading” o ers a solution, which means strings stretched every 10 meters across the pond surface. To some extent this arrangement prevents the birds from making a risk-free departure with a full stomach especially if a hunter is in attendance. Another e ect of climate change is the increasingly frequent heatwaves and periods without precipitation, especially in spring and summer which, in addition to a ecting the level of water in the ponds, is not favourable for fodder production either. Fluctuations in feed prices make preliminary calculations of the yield connected to feed uncertain and di cult to plan. Production results based on the earlier used technology of the company (0.3 tonnes of stocking/ha) approach guidelines for extensive production (0.15-0.2 tonnes of stocking/ ha), where sh are raised to market size based on natural food, with a minimum amount of additional feeding.

Hortobágy Fish Farm may not be as much a ected by the lack of water due to droughts as Transdanubian dam ponds, which were created by blocking a stream. e water supply of such ponds depends on the ow of water in the stream. Water ow of the Tisza River which feeds the farm is usually adequate, although water restrictions have also appeared in recent years. However, there have been several years where the reuse of ponds harvested during the summer to increase pro tability has been impossible due to an inadequate water supply. Evaporation from a huge area can be as much as 2-3 cm/day in hot weather, which requires a lot of replacement water to maintain the average operating water level of 120 cm.

In-house laboratory monitors a wide range of parameters

e company operates its own laboratory where water chemistry and plankton tests are performed, together with other examinations related to production. Monitoring water quality and especially oxygen levels is very important as sh are very sensitive to this parameter, especially when water temperature unexpectedly rises. By jointly analysing plankton and water chemistry it is possible to foresee what kind of intervention is needed to prevent sh mortality in ponds. During plankton investigation types of zooplankton and qualities of algae are determined. If blue-green algae (harmful algae) are detected in the water of the pond, which are not consumed by zooplankton or sh and can also produce toxins, intervention is needed, which usually means a bleach powder treatment. Algae are photosynthesising organisms, the amount and species composition of which also a ects the amount of oxygen. During the day they produce oxygen, but at night they consume it. At the end of the summer as the harvesting season approaches nights become longer, and diurnal oxygen producers consume more oxygen during the night. Additionally, some of the sh have reached market size and consume more oxygen. Demand for oxygen is thus high at a time when supply may be constrained. is can be prevented from potentially becoming fatal by ensuring a water ow in the ponds and by using aerators.

Oxygen saturation of water is a very important factor during the wintering period, too, as during this period a lot of fish are present in a relatively small area. Adequate oxygen saturation can only be guaranteed in high quality, uncontaminated water. Climate change has fundamental effects on the technology used by Hortobágy Fish Farm and more generally on the production of carp in polyculture at farming sites across the country.

Eva Kovacs, Euro sh, eva@euro sh.dk

Hortobágy Fish Farm

Hortobágyi Halgazdaság Zrt Halasto 02755/8 hrsz.

4071 Hortobágy

Hungary

Tel: +36 52 369 110 info@hhgzrt.hu, https://hhgzrt.hu/

Managing director: Róbert Pásztor

Activity: Production of carp and associated species in ponds

Total pond volume: 3,000 ha

Number of ponds: 6

A Hungarian perspective on the sustainability of pond sh aquaculture

Species: Common carp (70%), silver, bighead, grass carp, European cat sh, perch, pike, crucian carp

Volume of common carp: around 1.200 tonnes of table sh

Markets: Hungary, Romania

Product forms: Whole round, gutted, llets, portions, live sh is exported

Channels: Retail chains in Hungary, importers in Romania (a big wholesaler and some small retailers)