Játtað í:
2009

Granskingarøki:
Náttúra of náttúrutilfeingi

Verkætlanarslag:
R&D

Verkætlanarheiti:
Styring av planktonproduksjonen i færoyske bassenger

Játtanarnummar:
0419

Verkætlanarleiðari:
Arne G. Kolbeinshavn

Stovnur/virki:
Fiskaaling

Verkætlanarskeið:
1.12010-31.12.2010

Stuðul úr Granskingargrunninum:
301.000 kr.

Verkætlanarlýsing:
Original:

There are two different start-feeding methods for cod larvae. One method is called semi-intensive - and the other intensive. In the first method the larvae feed on zooplankton that is filtered from the pond/basin. (Kolbeinshavn 2005). In the second method the larvae are fed with enriched Rotifer. It has been closed down a massive research effort to design a diet to the rotifer, so that the enriched animals should be a copy of the plankton in nature, with respect to nutritional content. It has so far proven very difficult to achieve this goal, and therefore cod juveniles who are startfeeding on zooplankton, is a lot more viable juvenile cod. This is clearly presented in Imsland et al. (2006) research, which concluded that the larval diet is an important and decisive factor for juvenile growth potential, general juvenile quality and adaptability to environmental changes. Cod larvae in Imslands experiment that were fed with natural zooplankton grew up to 12 times better, 50 days after hatching than cod that were fed on enriched Rotifers. On the basis of this it can be concluded that Rotifer diet is missing something fundamental.

Fiskaalings research station in Nesvik has in the past four years startfed cod larvae by the semi-intensive method. Here we have used the natural method, where the larvae diet has been natural zooplankton. This fish fry was used in large-scale trials in Àrnafjørdur, and the results from this experiment are the best ever achieved, both in terms of growth and late maturation. It must be added that the temperature of the Faroe Islands is ideal for cod farming, and that this probably is a main reason for the good growth of the cod, but we also believe that the good growth performance and the late sex maturation, in large part due to that we have used natural zooplankton (mainly copepods) in the experiment.

Today, most fish farmers in Norway use cod fry that has been produced by the intensive method (Rotifer). This fish is early sexual mature, causing poor growth and poor earnings for the farmers. In the experiment in Àrnafjørdur (Kolbeinshavn et al. 2009), where it was used natural zooplankton, the light-controlled fish were sexually mature when it was 5.0 kg. These results are far better than previously published results, in terms of growth as well as late maturation. Since it is now the consensus among scientists, that natural zooplankton results in better growth than intensively produced fry (Imsland et al. 2006), and that the larvae may cause later maturation, it is more important than ever to intensify the research towards a better understanding of the mechanisms that control the production of copepods in the pond / basins. Furthermore, it also is cheaper to start feeding the larvae with zooplankton than Rotifer, which is a competitive advantage that is important for a future Faroese cod farming.

The aim of this experiment is to gain a better understanding maintaining copepod level on a stable level in pond / basins, so that it can be predictable, what can be harvested from the system. The experiments will aim to produce algal cultures resulting in a high and stable output over a longer period of time. It is also very important in this experiment, that one can gain an understanding of what is needed, to maintain the right copepods over a longer period, than is the case today. The goal is to run 4 startfeedings per year with zooplankton from ponds/basins, compared to just one today. To achieve this goal there will be conducted detailed studies of the planktonic ecosystem processes in the basins in Nesvik. The objective is to obtain the necessary knowledge to be able to control a high and stable production of relevant food for fish larvae. When this goal is achieved, then the Faroese farmers get a quality fry of cod, which are prerequisites to success in cod farming

Final:

Many studies have shown that feeding reared fish larvae on a natural zooplankton diet rather than on an enriched rotifer diet, significantly enhances the juvenile growth potential, quality and health. In 2002 the Aquaculture Research Station of the Faroes (Fiskaaling) began focusing on the opportunity of rearing Faroese cod larvae on zooplankton in basins in Nesvík. To optimise the potential of the plankton production capacity in three basins at The Marine Station in Nesvík, better understanding of the underlying mechanisms in the planktonic ecosystem, is required. Thus, the aim of the experiment was to closely monitor phyto- and zooplankton abundance and community structure. Aiming to achieve a high and stable plankton production from March-April to October, optimal conditions in the basins were created by a) pumping seawater into the basin, b) a pump, making the water turbulent and c) artificial fertilisation. To determine the importance of diatom growth for the zooplankton community, silicate was added to two basins whilst the third basin received no silicate.

There was a long lag period from fertilisation to phytoplankton response. This created periodically excessive amounts of nutrients in the basins and also fluctuations in primary production and phytoplankton abundance. The oxygen concentration commonly ranged from 100 to 130%. Chl a was variable throughout the experimental period, commonly ranging high above the desired values of 15-20 μg L-1. Some leakage occurred between the basins and thus the influence of a diatom vs. dinoflagellate community to zooplankton production could not be established. The diatoms Skeletonema costatum, Leptocylindrus danicus and Chaetoceros sp. dominated the phytoplankton community over prolonged periods. However in one of the basins dinoflagellates were abundant until late June. There was no relationship between the chl a concentration and the above mentioned parameters since, most likely, the phytoplankton production was in excess.'

The species composition was markedly different from that in the sea adjacent to the basins. The copepod Eurytemora spp. was the dominant zooplankton species throughout the season. There was a continuous egg production of Eurytemora spp. during the experimental period. However, there was no relationship between the rates of egg production and chl a concentrations, which is probably due to the 3 excessive quantities of chl a. It is likely that three generations of Eurytemora spp. were produced from April to October. However, most of the time, the community consisted of all developmental stages, revealing large overlaps between the generations.

Based on optimal conditions in the basins, the systems could theoretically support a maximum of around 0.6 to 1 million cod larvae. These are significantly larger quantities compared to the approximate 180,000 cod larvae used the first time the basins were manipulated in 2006 (Kolbeinshavn et al., submitted).

Although phytoplankton and zooplankton concentrations showed rather large temporal variations, the basins revealed that a high plankton production cycle can be maintained from March-April to November. Together with other positive characteristics such as the dominance of a calanoid species, mixed developmental stages and stable and long-lasting fecundity, it is worth further investigation on how to achieve a more stable production of zooplankton to startfeed fish larvae.

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Avrik:
Verkætlanarfrágreiðing er skrivað. Hon er at finna á www.fiskaaling.fo og á www.hav.fo.

Grein ” Stýring av ætiframleiðslu í hyljunum í Nesvík” er skrivað í Alitíðindi nr. 3, 2011, sum er at finna á www.fiskaaling.fo.



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