Warmer water is likely to boost fish appetites
This article was featured in Eurofish Magazine 3 2022.
Farming in shallow water bodies comes with a limited buffer in relation to air temperature changes, therefore Hungarian carp aquaculture is highly vulnerable to changes in climate. Furthermore, barrage dam pond farms, accounting for one-third of total carp production, are extremely sensitive to meteorological conditions since their water supply varies with seasonal precipitation over a relatively small catchment area.
Since records of temperature began in Hungary, 2019, 2018, 2014, 2015, and 2020 were the 1st, 2nd, 3rd, 4th, and 8th hottest years, respectively, so farmers already have firsthand experiences with the growth response of fish and the whole aquatic community to warmer waters. Water scarcity and low stream-flow rates in supplying watercourses in the late winter and early spring periods of 2020 and 2022 hindered barrage pond farmers in reaching operational water levels in ponds, while evaporation losses could not be covered during the extraordinary summer drought of 2021.
More research required to properly understand impacts of climate change
The impacts were reduced production space, concentrated nutrient levels, and low dissolved oxygen levels. From retrospective analysis, quantifying the impact of the meteorological situation is challenging, since it is hard to decouple the effects of climate drivers from that of managerial interventions taken as an adaptive response. However, a slight positive correlation between carp yields and temperature is observed if looking at the industrial data of the past two decades. To understand the multifaceted effects of climate change on pond aquaculture, including impacts on the pond food web and water quality, metabolic responses of farmed species, the emergence of new pathogens, and changes in disease transmission patterns, methodologically sound research actions must be taken.
Recently EU funded two Horizon projects (www.climefish.eu, www.ceresproject.eu) focusing on adapting the European aquaculture sector to changing climate. Both projects scoped the Central European carp farming sector, investigating the impacts in different countries, in different time horizons, and with different simulation modelling tools. Nevertheless, the most important finding is that water temperatures in carp farming regions of Europe will unlikely exceed the thermal optimum of common carp, therefore temperature increase will positively influence metabolic activity (growth potential, appetite) of the main farmed species. Analysis of model simulations for different management scenarios shows for Hungary that the maximal benefit of warmer temperatures is reaped with stocking rates lower and feeding rates higher than current practice. Reduced stocking rates and lower predation pressure on zooplankton biomass will help to exploit the advantages of increasing dynamics in the pond food web.
Multiple negative effects are likely with warming weather
Management risks and frequency of undesirable events will also increase, including water quality problems and the occurrence of diseases. It is forecast that the frequency of intensive rainfalls will increase with changing climate, which will increase the concentration of nutrients and toxic products in surface waters (due to land erosion and agricultural run-off waters). This will be exacerbated by more intense evaporation of water bodies, which will further increase the concentration of all substances. Water shortage is as well a common concern driven by climate. In Hungary, there is evidence of the adverse impact of climate change on discharges at watercourses, which may create a supply shortage, especially for barrage ponds. For round dam ponds, increased evaporation and hydrologic deficit of ponds during summer can be aggravated by decreased summer runoff from the Danube and its tributaries owing to earlier snowmelt in upper watersheds as forecast by hydrologic climate models. Increasing use of supplementary water will increase production costs if the cost of water increases. Based on model simulations it is also forecast that altering thermal conditions will favour the proliferation of Cyprinid herpesvirus and carp edema virus.
Recommended adaptation strategies consist of developing information systems for monitoring and mapping disease incidents and their patterns of distribution; using real time/in situ diagnostics to monitor water quality and fish health; applying stocking rate and biomass management resilient to hot summer weather; and the use of aerators and other oxygen manipulation techniques.
Research Institute for Fisheries and Aquaculture (HAKI)
Anna-liget utca 35
+36 66 515 300