Iodine nutrition and toxicity in Atlantic cod (Gadus morhua) larvae

-Copepods as feed promote better growth and development in marine fish larvae than rotifers. However, unlike rotifers, copepods contain several minerals such as iodine (I), at potentially toxic levels. Iodine is an essential trace element and both under and over supply of I can inhibit the production of the I containing thyroid hormones. It is unknown whether marine fish larvae require copepod levels of I or if mechanisms are present that prevent I toxicity. In this study, larval Atlantic cod (Gadus morhua) were fed rotifers enriched to intermediate (26 mg I kg-1 dry weight; MI group) or copepod (129 mg I kg-1 DW; HI group) I levels and compared to cod larvae fed control rotifers (0.6 mg I kg-1 DW). Larval I concentrations were increased by 3 (MI) and 7 (HI) fold compared to controls during the rotifer feeding period. No differences in growth were observed, but the HI diet increased thyroid follicle colloid to epithelium ratios, and affected the essential element concentrations of larvae compared to the other groups. The thyroid follicle morphology in the HI larvae is typical of colloid goitre, a condition resulting from excessive I intake, even though whole body I levels were below those found previously in copepod fed cod larvae. This is the first observation of dietary induced I toxicity in fish, and suggests I toxicity may be determined to a greater extent by bioavailability and nutrient interactions than by total body I concentrations in fish larvae. Rotifers with 0.6 mg I kg-1 DW appeared sufficient to prevent gross signs of I deficiency in cod larvae reared with continuous water exchange, while modelling of cod larvae versus rotifer I levels suggests that optimum I levels in rotifers for cod larvae is 3.5 mg I kg-1 DW

Rapport/Report 38/2016 – English summary

-Identifisering av laks på individnivå, brukt blant annet i forskning og i avlsarbeid, benytter i dag PIT-tag. Dette er små merker som injiseres i bukhulen. I dette forprosjektet ble irisskanning testet opp mot PIT-tag som metode for identifisering på individnivå. Irisskanning krever ikke inngrep i fisken og den etterlater ingen fremmedlegemer. Forprosjektet er et første steg i «proof of concept» for irisskanning som metode for identifisering av laks på individnivå. Totalt 100 fisk ble identifisert med både PIT-tag og irisskanning, dvs samme løpenummer. I tillegg var åtte fisk PIT-tagget men uten ID i irisdatabasen. Fisk ble deretter testet for gjenkjenning med irisskanneren med fasit i PIT-tag. Med unntak av en fisk som en gang ble identifisert feil (annet individnummer oppgitt) ble fisken enten korrekt identifisert eller identifisert som ukjent. Forprosjektet kan derfor ikke sies å være en ubetinget suksess. Metoden vurderes allikevel som lovende siden det er flere klare forbedringer i utstyr og bruken av dette som foreligger. Rapporten tar for seg flere forbedringsfaktorer som må på plass i eventuelt videre arbeid med «proof of concept».Identification of salmon at the individual level, commonly used in research and breeding programs, currently uses PIT-tags. These small marks are injected into the abdominal cavity. In this pilot project iris scanning was tested against PIT tags as a method for identification of individuals. Iris scanning does not require intervention in the fish and it leaves no foreign material. The pilot project is a first step in a "proof of concept" for iris scanning as a method for identification of salmon at the individual level. A total of 100 fish were identified with both PIT-tag and iris scanning, that is they were given the same ID number. In addition, eight fish were PIT-tagged but without ID in the iris database. The fish were tested for recognition with iris scanner with reference to the PIT-tag database. With the exception of one fish that was once identified erroneously (another individual), the fish were either correctly identified or identified as unknown. The pilot project was not an unqualified success. The method is, however, considered promising since there are clear possibilities for improvements in both the equipment per se and in the use of this. The report covers several improvement factors that must be in place in any future work on "proof of concept"

Rapport/Report 39/2016 – English summary

-Identifisering av laks på individnivå, brukt blant annet i forskning og i avlsarbeid, benytter i dag PIT-tag. Dette er små merker som injiseres i bukhulen. I et forprosjekt finansiert av FHF ble irisskanning testet opp mot PIT-tag som metode for identifisering på individnivå. Med bakgrunn i forprosjektet ble flere faktorer forbedret. Fase 2 er neste steg i «proof of concept» for irisskanning som metode for identifisering av laks på individnivå, og består av to separate forsøk. Forsøk 1. Det ble etablert to databaser, en for PIT-tag og en for irisskanneren med samme ID på 104 fisker. Av disse ble to fisker ikke gjenkjent og 102 fikk rett ID. Det ble på bakgrunn av disse gode resultatene besluttet at prosjektet skulle gå videre og forsøk 2 skulle gjennomføres. Forsøk 2. Databaser ble etablert i november 2015, og fisken skulle testes for rett ID gjennom smoltifiseringsprosessen. ID ble testet etter mørket (lysstyringsperiode kort dag), etter kontinuerlig lys og etter seks uker i sjø. Test 1 (etter mørkefasen) viste rett ID på 81% av fisken, feil ID på 15% av fisken og usikker ID på 4% av fisken. Test 2 og Test 3 ble gjennomførte med andre kamera enn det databasene var etablert med og kan derfor ikke vurderes. Rapporten tar for seg flere forbedringsfaktorer som må på plass i eventuelt videre arbeid med «proof of concept».Identification of salmon at the individual level, commonly used in research and breeding programs, currently uses PIT-tags. These small marks are injected into the abdominal cavity. In a pilot project funded by FHF iris scanning was tested against PIT-tag as a method for identification of individual salmon. Based on results from the pilot project several factors were improved. Phase 2 is the next step in the "proof of concept" for iris scanning as a method for identification of salmon at the individual level, and consists of two separate experiments. Experiment 1. Two databases were established, one for PIT tag and one for iris scanner with the same ID on 104 fishes. Of these, two fish were unrecognized and 102 fish got the correct ID. Based on these good results the project decided to go ahead and experiment 2 was to be performed. Experiment 2. Databases were established in November 2015, and the fish should be tested for ID through the salmon smoltification process. IDs were tested after dark (light controlled short day), after continuous light and after six weeks at sea. Test 1 (after the dark phase) showed correct ID of 81% of the fish, erroneous ID of 15% of the fish and insecure ID of 4% of the fish. Test 2 and Test 3 was conducted with other cameras than what the databases were established with and therefore cannot be considered. The report covers several improvement factors that must be in place in any future work on "proof of concept"

Iodine nutrition and toxicity in Atlantic cod (Gadus morhua) larvae

Copepods as feed promote better growth and development in marine fish larvae than rotifers. However, unlike rotifers, copepods contain several minerals such as iodine (I), at potentially toxic levels. Iodine is an essential trace element and both under and over supply of I can inhibit the production of the I containing thyroid hormones. It is unknown whether marine fish larvae require copepod levels of I or if mechanisms are present that prevent I toxicity. In this study, larval Atlantic cod (Gadus morhua) were fed rotifers enriched to intermediate (26 mg I kg-1 dry weight; MI group) or copepod (129 mg I kg-1 DW; HI group) I levels and compared to cod larvae fed control rotifers (0.6 mg I kg-1 DW). Larval I concentrations were increased by 3 (MI) and 7 (HI) fold compared to controls during the rotifer feeding period. No differences in growth were observed, but the HI diet increased thyroid follicle colloid to epithelium ratios, and affected the essential element concentrations of larvae compared to the other groups. The thyroid follicle morphology in the HI larvae is typical of colloid goitre, a condition resulting from excessive I intake, even though whole body I levels were below those found previously in copepod fed cod larvae. This is the first observation of dietary induced I toxicity in fish, and suggests I toxicity may be determined to a greater extent by bioavailability and nutrient interactions than by total body I concentrations in fish larvae. Rotifers with 0.6 mg I kg-1 DW appeared sufficient to prevent gross signs of I deficiency in cod larvae reared with continuous water exchange, while modelling of cod larvae versus rotifer I levels suggests that optimum I levels in rotifers for cod larvae is 3.5 mg I kg-1 DW