Most articles mentioning allergy to mackerel describe allergy to fish in general without attributing symptoms specifically to mackerel. 

Hamada et al. (2003) [1395] list the symptoms of the 5 patients who provided sera as urticaria in all 5 cases with additional symptoms of asthma for one patient and diarhoea for another.

Helbling et al. (1996) [1727] describe the symptoms of 39 patients as pruritus (27/39), hives (27/39), asthma and wheezing (21/39), angioedema (20/39), dyspepsia and cramps (7/39), vomiting (3/39), shock (3/39) and fainting (2/39). Only 4/39 patients had a history of allergic reaction following ingestion of mackerel but 20/39 had a positive SPT and 9/23 a positive RAST to mackerel.

Bernhisel-Broadbent et al. (1992) [1397] describe symptoms on challenge with other fish species as oral pruritis in 10/11 patients together with cutaneous symptoms (urticaria, angioedema, pruritis or erythema) in 6, gasterointestinal in 2, while one patients showed laryngeal symptoms and another wheeze.  

de Martino et al (1990) [1681] also noted that 1/20 cod allergic children had a clinical history of reaction to mackerel although only 4/20 children reported ever eating mackerel. 

Helbling et al. (1996) [1727] made an extract of Alaska pollack and of 4 crustacean species. 16 commercial extracts of fish, including mackerel, and 12 commercial extracts of inhalant allergens were also used .

Bernhisel-Broadbent et al. (1992) [1397] added 10 g. of raw or cooked fish (catfish, bass, perch, mackerel, tuna, salmon, trout, codfish and flounder) to 40 ml. phosphate buffered saline in centrifuge tubes with a glass marble. The tubes were placed in a test tube rotator overnight at 4°C. Samples were centrifuged at 1250 x g for 15 min and then at 16000 x g for 15 min. Supernatants were lyophilized. Skin tests used extracts of raw fish, probably reconsituted 1:20 (w/v). Commercial sardine extract was used (Greer laboratories, Lenoir, NC). 

de Martino et al (1990) [1681] used commercial extracts (Lofarma, Milan, Italy). The extracts were diluted 1:20 (w/v) in a glycerol solution.

Helbling et al. (1996) [1727] defined a positive skin prick as producing a 3 mm diameter wheal in a patient who reacted to the positive control (1 mg/ml histamine diphosphate) and not to 50% (v/v) glycerol in PBS. Results were recorded after 15 minutes.

Bernhisel-Broadbent et al. (1992) [1397] used 1 mg/ml histamine as a positive control and saline as a negative control. Wheal with diameters 3 mm greater than the negative control were considered positive.

de Martino et al (1990) [1681] used histamine hydochloride, 1 mg/ml, as a positive control and a glycerol solution as a negative control. Diameters were read after 15 minutes and reactions half or more than the size of the positive control, read after 10 minutes, were considered positive. 

Helbling et al. (1996) [1727] tested 35 out of 39 study subjects with mackerel together with 18 atopic control subjects.

Bernhisel-Broadbent et al. (1992) [1397] tested 11 patients with histories of fish allergy and 20 controls including 10 atopic patients with other food allergies.

de Martino et al (1990) [1681] tested 20 cod allergic children and 40 children who had a positive SPT and RAST to a different food.

Helbling et al. (1996) [1727] found that 21/35 fish allergic subjects gave a positive skin test to mackerel. One atopic control subject also reacted.

Bernhisel-Broadbent et al. (1992) [1397] reported that 8/11 patients gave positive SPTs with mackerel extract. The wheal diameters of positive tests were 6-26 mm. For comparison, the least reactive was sardine with 8 positive and 4-8 mm diameters while cod extract produced 9/11 positive wheals with 4-40 mm diameters.

de Martino et al (1990) [1681] reported that only 4/20 of the cod allergic children reacted to mackerel extract and none of the cod negative children reacted.

Hamada et al (2004) [1392] used natural and recombinant parvalbumin from pacific mackerel, Scomber japonicus.

Hamada et al (2003) [1395] used purified parvalbumin from pacific or chub mackerel, Scomber japonicus, Atlantic mackerel (Scomber scombrus) and blue mackerel (Scomber australasicus).

Hamada et al (2003) [1800] used purified collagen from Japanese eel, alfonsin, mackerel, skipjack and bigeye tuna and also purified parvalbumin from bigeye tuna.   

Helbling et al. (1996) [1727] made an extract of Alaska pollack, anchovy, mackerel, rainbow trout, salmon and tuna by blending 500g of raw fish in 1L of 0.01M PBS, pH 7.2, in a Waring blender for 1-3 minutes at room temperature. The mixture was extracted overnight at 4°C and centrifuged (70,000 x g). Supernatants were concentrated  with an Amicon YM1 filter (molecular weight cut-off 1 kDa) and recentrifuged (180,000 x g). Commercial extracts of bass, catfish, codfish, haddock, perch, sardine, herring, snapper, sole and whitefish were dialysed against 0.1 M borate, ph 8.0, and concentrated by dialysis against Ficoll 400 (Pharmacia). Cyanogen bromide activated paper disks were loaded to 50 μg protein per disk for RAST.

Bernhisel-Broadbent et al. (1992) [1397] used the extracts described for skin tests.

Hamada et al (2004) [1392] used ELISA and ELISA inhibition.

Hamada et al. (2003) [1395] and Hamada et al (2003) [1800] used CAP-RAST, ELISA, and ELISA inhibition.

Helbling et al. (1996) [1727] used RAST and RAST inhibition. A positive RAST was ≥3% binding of the added radioactivity.

Bernhisel-Broadbent et al. (1992) [1397] used immunoblotting.

Hamada et al (2004) [1392] used sera from 2 fish allergic patients.

Hamada et al (2003) [1395] used sera from 5 fish allergic patients.

Hamada et al (2003) [1800] used sera from 15 fish allergic patients.

Helbling et al. (1996) [1727] used sera from 23 fish allergic patients.

Bernhisel-Broadbent et al. (1992) [1397] used sera from 11 fish allergic patients

Hamada et al (2004) [1392] reported an IgE binding inhibition study of natural and recombinant mackerel (Scomber japanicus) parvalbumin against purified parvalbumins from Japanese eel, horse mackerel, red sea bream, skipjack, bigeye tuna and Japanese flounder. They concluded that there was significant IgE cross-reactivity between mackerel and other fish parvalbumins and that the recombinant mackerel parvalbumin could be used to diagnose fish-allergy.

Hamada et al. (2003) [1395] report the CAP-RAST classes of their 5 subjects:
Subject 1 - salmon (3) and cod (3)
Subject 2 - salmon (4) and cod (3)
Subject 3 - salmon (3), cod (3), horse mackerel (3) and mackerel (3)
Subject 4 - sardine (3), salmon (3), cod (3), horse mackerel (3), mackerel (3) and tuna (3)
Subject 5 - cod (4), horse mackerel (3), mackerel (3) and tuna (4)
By ELISA, four of the five patient sera tested reacted to all the purified mackerel parvalbumins. Serum from patient 5 was found to react to collagen but not to parvalbumin.

Hamada et al (2003) [1800] also reported CAP-RAST classes against several species of fish for 15 fish allergic patients, probably including some of those of Hamada et al. (2003) [1395]. 4/15 sera were found to react with bigeye tuna collagen by ELISA and 3 of these were tested to show that collagen extracted from Japanese eel, alfonsin, mackerel, skipjack and bigeye tuna gave similar IgE binding.  

Helbling et al. (1996) [1727] reported a positive RAST with mackerel for 9/23 fish-sensitive subjects, which was the third lowest response rate of the 20 fish tested. The proportion of positive responses varied from 8/11 for cod and 8/12 for haddock to 4/29 for anchovy and 5/27 for tuna. It had been suggested that some positive SPTs with commercial fish extracts were due to histamine contamination and in this study 13/18 and 5/18 atopic controls reacted to anchovy and tuna respectively. However, the correlation for mackerel between RAST and SPT results with 5.2% of radioactivity bound by sera from SPT positive subjects and 1.3% bound by sera from SPT negative subjects suggests that the SPT results were not influenced by histamine. RAST inhibition of mackerel was greatest for anchovy extract, 80% (only slightly less than mackerel extract), with salmon near 40% and tuna near 20%.

Bernhisel-Broadbent et al. (1992) [1397] separated proteins by SDS-PAGE by the method of Dreyfuss et al. (1984) [1799].

Bernhisel-Broadbent et al. (1992) [1397] showed that IgE from the sera of a salmon allergic patient recognised a 13 kDa allergen in extracts of several raw and cooked fish including mackerel. Sera from a flounder allergic patient did not recognise salmon extract but did bind to the 13 kDa band in mackerel.